Abstract of lectures on the discipline “Automated electric drive. Variable frequency asynchronous electric drive - a course of lectures Automated electric drive a course of lectures
In the tutorial that is brought to your attention, the tutorial will focus on the basics of the electric drive and its most promising form - an asynchronous frequency-controlled electric drive. The manual is intended for workers involved in the promotion of complex electrical products on the market, which is automated electric drives and for students of electrical specialties.
Lecturer: Onishchenko Georgy Borisovich. Doctor of technical sciences, professor. Full member of the Academy of Electrotechnical Sciences of the Russian Federation.
The series of video lectures covers the following topics:
1. Functions and structure of an automated electric drive.
2. General characteristics of an adjustable electric drive.
3. The principle of operation of an asynchronous motor.
4. Frequency regulation of the speed of an asynchronous motor.
5. Power controlled semiconductor devices.
6. Structural diagram of the frequency converter.
7. Autonomous voltage inverter. The principle of pulse-width modulation.
8. Rectifier and DC link as part of the frequency converter.
9. Structural diagrams of regulation of frequency-controlled electric drive.
10. Features of high-voltage frequency converters.
11. Fields of application of frequency-controlled electric drive.
Consideration of these issues will allow you to get a fairly complete picture of the composition, principles of operation, circuit design, technical characteristics and areas of application of a frequency-controlled asynchronous electric drive.
Lecture 1. Functions and structure of an automated electric drive
The objectives of the first lecture are to give an idea of the role and importance of an automated electric drive in modern industrial production and in the country's electric power system.
Lecture 2. Adjustable electric drive - the main type of modern electric drive
General issues related to the creation and use of adjustable electric drives are considered.
Lecture 3. The principle of operation of an asynchronous electric motor
Design features and main characteristics of the most common electrical machines - asynchronous motors. These motors are widely used in industry, agriculture, public utilities and other fields. The power range of manufactured asynchronous motors is very wide - from hundreds of watts to several thousand kilowatts, but the principle of operation of these machines is the same for all sizes and modifications.
Lecture 4
The most effective way to control the speed of an induction motor is to change the frequency and amplitude of the three-phase voltage applied to the windings of the induction motor. In recent years, this control method has received the widest application for electric drives for various purposes, both low-voltage with voltages up to 400 V and high-voltage high-power drives with voltages of 6.0 and 10.0 kV.
This section outlines the principles of controlling the motor speed by changing the frequency of the input voltage, provides possible algorithms for changing not only the frequency, but also the voltage amplitude, and analyzes the drive characteristics obtained with the frequency control method.
Lecture 5. The principle of operation and structure of the frequency converter
The creation and mass production of fully controlled power semiconductor devices had a revolutionary impact on the development of many types of electrical equipment, primarily on the electric drive. New fully controllable semiconductor devices include insulated gate bipolar transistors (IGBTs) and combination gated thyristors. Based on them, it became possible to create frequency converters for powering AC motors and smooth regulation of their rotation speed. In this section, the characteristics of new power semiconductor devices are considered and their parameters are given.
Lecture 6. Scalar motor control systems
For electric drives operating with a limited speed control range and in cases where high speed and control accuracy are not required, simpler scalar control systems are used, which are discussed in this section.
Module No. 7 "Vector control of frequency-controlled electric drives"
Vector control of an asynchronous motor is based on fairly complex algorithms that reflect the representation of electromagnetic processes in the motor in vector form. In this lecture, we will try to present the basics of vector control in a somewhat simplified way, avoiding complex mathematical calculations.
There will be a continuation soon!
transcript
1 A.V. Romanov ELECTRIC DRIVE Course of lectures Voronezh 006 0
2 Voronezh State Technical University A.V. Romanov ELECTRIC DRIVE Approved by the Editorial and Publishing Council of the University as a textbook Voronezh 006 1
3 UDC 6-83(075.8) Romanov A.V. Electric drive: Course of lectures. Voronezh: Voronezh. state tech. un-t, s. The course of lectures deals with the issues of construction of electric drives of direct and alternating current, analysis of electromechanical and mechanical characteristics of electric machines, principles of control in an electric drive. The publication complies with the requirements of the State Educational Standard of Higher Professional Education in the direction of "Electrical Engineering, Electromechanics and Electrotechnology". The course of lectures is intended for second-year students of the specialty "Electric Drive and Automation of Industrial Installations and Technological Complexes" of full-time education on the basis of secondary vocational education. The publication is intended for students of technical specialties, graduate students and specialists involved in the development of electric drives. Tab. 3. Ill. 7. Bibliography: 6 titles. Scientific editor tech. sciences, prof. Yu.M. Frolov Reviewers: Department of Automation of Technological Processes, Voronezh State University of Architecture and Civil Engineering (Head of the Department, Doctor of Engineering Sciences, Prof. VD Volkov); Dr. tech. sciences, prof. A.I. Shiyanov Romanov A.V., 006 Design. GOUVPO "Voronezh State Technical University", 006
4 INTRODUCTION The electric drive (ED) plays an important role in the implementation of the tasks of increasing labor productivity in various sectors of the national economy, automation and complex mechanization of production processes. About 70% of the generated electricity is converted into mechanical energy by electric motors (EM), which set in motion various machines and mechanisms. A modern electric drive is distinguished by a wide variety of control means used from conventional switching equipment to computers, a large range of motor power, a speed control range of up to 10,000: 1 or more, and the use of both low-speed and ultra-high-speed electric motors. An electric drive is a single electromechanical system, the electrical part of which consists of an electric motor, converter, control and information devices, and the mechanical part includes all the associated moving masses of the drive and mechanism. The widespread introduction of electric drive in all industries and the ever-increasing requirements for the static and dynamic characteristics of electric drives place increased demands on the professional training of specialists in the field of electric drive. It should be noted that since full-time students on the basis of secondary specialized education are given a minimum number of study hours for mastering a specialty by the curriculum, progress in professional knowledge is highly dependent on the independent work of students. In particular, at the end of this edition there is a bibliographic list of scientific and technical literature recommended for study in addition to the proposed lecture notes. In addition, in addition to the course of lectures, a laboratory workshop on electric drive was released, which addresses the issues of experimental research 3
5 electric drives of direct and alternating current. For more successful mastering of the discipline, students are advised to study the text of lectures and the content of laboratory work in advance. The State Educational Standard of Higher Professional Education of the Russian Federation regulates the following mandatory topics for the training course in the discipline "Electric Drive". EXTRACT from the State educational standard of higher professional education of state requirements for the minimum content and level of training of a certified engineer in the direction of "Electrical Engineering, Electromechanics and Electrotechnology", specializing in "Electric Drive and Automation of Industrial Installations and Technological Complexes" OPD.F. 09. "Electric drive" Electric drive as a system; block diagram of the electric drive; mechanical part of the power channel of the electric drive; physical processes in electric drives with DC machines, asynchronous and synchronous machines; electrical part of the power channel of the electric drive; principles of control in the electric drive; element base of the information channel; synthesis of structures and parameters of the information channel; design elements of the electric drive. The material of this course of lectures is fully consistent with this topic. 4
6 LECTURE 1 HISTORY OF THE DEVELOPMENT OF THE ELECTRIC DRIVE AS A BRANCH OF SCIENCE AND TECHNOLOGY Issues addressed in the lecture. 1. Brief historical background on the development of AC and DC electric drives. Works of domestic and foreign scientists. 3. The role of the electric drive in the national economy. 4. Structure and main elements of a modern automated electric drive. Electric drive is a relatively young branch of science and technology, with a little more than a century since its practical application. The emergence of EP is due to the work of many domestic and foreign scientists in electrical engineering. This brilliant series includes the names of such prominent scientists as the Dane H. Erested, who showed the possibility of interaction between a magnetic field and a conductor with current (180), the Frenchman A. Ampère, who mathematically formalized this interaction in the same 180, the Englishman M. Faraday, built in 181 an experimental installation that proved the possibility of building an electric motor. These are domestic academicians B.S. Jacobi and E.H. Lenz, who first managed to create a direct current electric motor in 1834. The work of B.S. Jacobi on the creation of the engine gained wide world fame, and many subsequent works in this area were a variation or development of his ideas, for example, in 1837 the American Davenport built his electric motor with a simpler commutator. In 1838 B.S. Jacobi improved the design of the ED, introducing into it almost all the elements of a modern electric machine. This electric motor, with a power of 1 hp, was used to drive a boat, which, with 1 passengers, moved at a speed of up to 5 km / h against the He-5 current.
7 you. Therefore, 1838 is considered the year of birth of the electric drive. Already on this first, still imperfect model of the electric drive, its very significant advantages were revealed in comparison with the steam mechanisms that prevailed at that time - the absence of a steam boiler, fuel and water supplies, i.e. significantly better weight and size indicators. However, the imperfection of the first ED, and most importantly, the uneconomical source of electricity of the galvanic battery, which was developed by the Italian L. Galvani (), caused the work of B.S. Jacobi and his followers did not immediately receive practical application. A simple, reliable and economical source of electrical energy was required. And the way out was found. Back in 1833, Academician E.Kh. Lenz discovered the principle of reversibility of electrical machines, which later combined the development of engines and generators. And in 1870, an employee of the French company "Alliance" Z. Gramm created an industrial type of DC electric generator, which gave a new impetus to the development of the electric drive and its introduction into industry. Here are some examples. Our compatriot electrical engineer V.N. Chikolev () creates in 1879 an EP for arc lamps, electric drives for a sewing machine (188) and a fan (1886), which were awarded gold medals at all-Russian exhibitions. There is an introduction of direct current electric current in the navy: an ammunition lift on the battleship "Sisoi the Great" (), the first steering gear on the battleship "1 Apostles" (199). In 1895 A.V. Shubin developed the "injector-engine" system for steering, which was later installed on the battleships "Prince Suvorov", "Slava" and others. a significant number of DC motors. 6
8 There are cases of using an electric drive in urban transport, tram lines in the cities of Kyiv, Kazan and Nizhny Novgorod (189) and somewhat later in Moscow (1903) and St. Petersburg (1907). However, the reported successes have been modest. In 1890, the electric drive accounted for only 5% of the total power of the mechanisms used. The emerging practical experience required analysis, systematization and development of a theoretical framework for subsequent coverage of the development of EP. A huge role here was played by the scientific work of our compatriot, the largest electrical engineer D.A. Lachinov (), published in 1880 in the journal "Electricity" under the title "Electromechanical work", which laid the first foundations of the science of electric drive. YES. Lachinov convincingly proved the advantages of the electrical distribution of mechanical energy, for the first time gave an expression for the mechanical characteristics of a DC motor with series excitation, gave a classification of electrical machines according to the method of excitation, and considered the conditions for supplying the engine from a generator. Therefore, 1880, the year of the publication of the scientific work "Electromechanical Work", is considered the year of the birth of the science of electric drive. Along with the DC electric drive, make your way into life and the AC drive. In 1841, the Englishman C. Whitson built a single-phase synchronous electric motor. But he did not find practical application due to difficulties during launch. In 1876, P.N. Yablochkov () developed several designs of synchronous generators to power the candles he invented, and also invented a transformer. The next step on the way to AC EP was the discovery in 1888 by the Italian G. Ferraris and Yugoslav N. Tesla of the phenomenon of a rotating magnetic field, which marked the beginning of the design of multi-phase electric motors. Ferraris and Tesla 7
9, several models of two-phase AC motors have been developed. However, two-phase current in Europe is not widely used. The reason for this was the development by the Russian electrical engineer M.O. Dolivo-Dobrovolsky () in 1889 for a more advanced three-phase alternating current system. In the same year, 1889, on March 8, he patented an asynchronous electric motor with a squirrel-cage rotor (AD short circuit), and somewhat later with a phase rotor. Already in 1891, at the electrical exhibition in Frankfurt am Main, M.O. Dolivo-Dobrovolsky demonstrated asynchronous electric motors with a power of 0.1 kW (fan); 1.5 kW (DC generator) and 75 kW (pump). Dolivo-Dobrovolsky also developed a 3-phase synchronous generator and a 3-phase transformer, the design of which remains practically unchanged in our time. Marcel Despres in 1881 substantiated the possibility of transmitting electricity at a distance, and in 188 the first transmission line was built with a length of 57 km and a power of 3 kW. As a result of the above works, the last fundamental technical obstacles to the spread of electrical energy transmission were eliminated and the most reliable, simple and cheap electric motor was created, which is currently enjoying exceptional distribution. More than 50% of all electricity is converted into mechanical power by means of the most massive electric drive based on short circuit AD. The first 3-phase AC EP in Russia were installed in 1893 in Shepetovka and at the Kolomensky plant, where by 1895 09 electric motors with a total capacity of 1507 kW were installed. And yet, the pace of introduction of the electric drive into the industry remained low due to the backwardness of Russia in the field of electrical production 8
10 (.5% of world production) and electricity generation (15th place in the world) even during the heyday of tsarist Russia (1913). After the victory of the Great October Revolution in 190, the question of a radical reorganization of the entire national economy was raised. The GOELRO plan (the state plan for the electrification of Russia) was developed, which provides for the creation of 30 thermal and hydroelectric power plants with a total capacity of 1 million 750 thousand kW (by 1935, about 4.5 million kW were commissioned). Working on the GOELRO plan, V.I. Lenin noted that "the electric drive just most reliably ensures any speed and automatic connection of operations in the most extensive field of labor." Why was so much attention paid to electric drive and electrification? The point is obvious that the electric drive is the power basis for performing mechanical work and automating production processes with high efficiency, while the electric drive creates all the conditions for highly productive work. Here is a simple example. It is known that during the working day one person can generate about 1 kW / h with the help of muscular energy, the cost of production of which is (conditionally) 1 kopeck. In highly electrified industries, the installed power of electric motors per worker is 4-5 kW (this indicator is called the electric power of labor). With an eight-hour working day, we get a consumption of 3-40 kW / h. This means that the worker controls the mechanisms, the work of which per shift is equivalent to the work of 3-40 people. Even greater efficiency of EP is observed in the mining industry. For example, on a walking excavator of the ESH-15/15 type, having an arrow of 15 meters and a bucket with a capacity of 15 cubic meters, the power of one asynchronous motor is 8 MW. At rolling mills 9
11 The installed power of ED is more than 60 MW, and the rolling speed is 16 km/h. That is why it was so important to ensure the widespread introduction of the electric drive in the national economy. Quantitatively, this is characterized by an electrification coefficient equal to the ratio of the power of electric motors to the power of all installed motors, including non-electric ones. The dynamics of the growth of the electrification coefficient in Russia can be traced in Table 1.1. The value of the electrification coefficient, % per year, about leading world powers. At present, EP has taken a dominant position in the national economy and consumes about one-third of the total electricity produced in the country (about 1.5 trillion kW/h). So what is an electric drive? According to GOST R, an electric drive is an electromechanical system consisting, in the general case, of interacting power converters, electromechanical and mechanical converters, control and information devices and interface devices with external electrical, mechanical, control and information systems, designed to set in motion executive bodies (IO ) working machine 10
12 Electrical network Converter device Electric motor device Control information device Transmission device Working machine Executive body electrical connection mechanical connection This definition is illustrated in Fig. Let's decipher the components. A converting device (electricity converter) is an electrical device that converts electrical energy with one parameter value and/or quality indicators into electrical energy with other parameter values and/or quality indicators. (Note that the parameters can be converted according to the type of current, voltage, frequency, number of phases, voltage phase, according to GOST 18311). Converters are classified by current (DC and AC), as well as thyristor and transistor converters by element base. eleven
13 Electric motor device (electromechanical converter) is an electrical device designed to convert electrical energy into mechanical energy or mechanical energy into electrical energy. The electric motors used in the electric drive can be of alternating and direct current. By power, electrical machines can be conditionally divided into: micromachines up to 0.6 kW. low power machines up to 100 kW. medium power machines up to 1000 kW. high power over 1000 kW. By rotation speed: low-speed up to 500 rpm. medium speed up to 1500 rpm. high-speed up to 3000 rpm. ultra-high-speed up to rpm. According to the rated voltage, there are low-voltage motors (up to 1000 V) and high-voltage motors (above 1000 V). Control information device. The control device is designed to generate control actions in the electric drive and is a set of functionally interconnected electromagnetic, electromechanical, semiconductor elements. In the simplest case, the control device can be reduced to a conventional switch that turns on the ED in the network. High-precision ED contain microprocessors and computers in the control device. The information device is intended for receiving, converting, storing, distributing and issuing information about the variables of the electric drive, the technological process and related systems for use in the electric drive control system and external information systems. The transmission device consists of a mechanical transmission and an interface device. A mechanical transmission is a mechanical converter designed to transmit 1
14 chi mechanical energy from ED to the executive body of the working machine and the coordination of the type and speed of their movement. The interface device is a set of electrical and mechanical elements that ensure the interaction of the electric drive with adjacent systems and individual parts of the electric drive with each other. Reducers, V-belt and chain drives, electromagnetic slip clutches, etc. can act as a transmission device. A working machine is a machine that changes the shape, properties, state and position of the object of labor. The executive body of a working machine is a moving element of a working machine that performs a technological operation. These definitions need to be supplemented. The electric drive control system is a set of control and information devices and ED interface devices designed to control the electromechanical energy conversion in order to ensure the specified movement of the working machine's executive body. The control system of the electric drive is a higher-level control system external to the electric drive that supplies the information necessary for the functioning of the electric drive. 13
15 LECTURE ELECTRIC DRIVE THE MAIN ELEMENT OF SYSTEMS OF COMPLEX MECHANIZATION AND AUTOMATION OF TECHNOLOGICAL PROCESSES IN MACHINE PRODUCTION Questions considered in the lecture. 1. Structural evolution of electric drives. Various types of electric drives used in industry and agriculture. 3. The main trends in the development of electric drives. 4. The structure of the EP from the standpoint of the "Theory of the electric drive". Over the years of its existence, the electric drive has undergone fundamental changes. First of all, methods of transferring mechanical energy from engines to working machines were improved. For example, in our country, before the beginning of the first five-year plan (198), a group electric drive "an electric drive with one electric motor that ensures the movement of the executive bodies of several working machines or several IO of one working machine" dominated, but by the end of the first five-year plan (193) it was withdrawn from industry . Fig..1 shows a functional diagram of a group electric drive of an enterprise. The peculiarity of this scheme is in the mechanical distribution of energy throughout the enterprise and, accordingly, in the mechanical control of the process, i.e. management of the work of the executive bodies of working machines. Figure .. shows another diagram of a group electric drive of a group electric drive of working machines. Unlike the previous scheme, the electrical energy here is supplied directly to the RM, and already in them it is mechanically distributed. The mechanical control of the work is preserved. Among the common disadvantages of a group electric drive are: step speed control; fourteen
16 Electrical network U, I electrical energy EM transmission shaft M, ω mechanical energy RM 1 RM IO 1 IO 3 IO 1 IO 3 Fig..1. Group electric drive of the enterprise Electric network ED 1 ED RM 1 RM IO 1 IO 3 IO 1 IO 3 Fig... Group electric drive of working machines small control range; dangerous working conditions; low performance. The group electric drive was replaced by a more promising and economical individual electric drive, this is "EP, providing the movement of one executive body of the working machine", the functional diagram is shown 15
17 in Fig..3. In this version of the electric drive, the distribution of electrical energy occurs up to the working bodies. It also becomes possible to control mechanical energy electrically. In addition, an individual drive makes it possible in some cases to simplify the design of the RM, since ED is often structurally a working body (fan, electric drill, etc.). Electrical network RM ED 1 ED ED 3 IO 1 IO IO 3 Fig..3. Individual electric drive At present, an individual electric drive is the main type of industrially used electric drive. But not the only one. In a number of production mechanisms, an interconnected electric drive is used - these are "two or more electrically or mechanically interconnected electric drives, during operation of which a given ratio of their speeds and (or) loads and (or) the position of the executive bodies of working machines" is maintained. This type of electric drive combines two types of electric drives - a multi-motor electric drive and an electric shaft. Multi-motor electric drive (Fig..4) "an electric drive containing several electric motors, the mechanical connection between which is carried out through the executive body of the working machine" . In a number of cases, such an electric drive makes it possible to reduce forces in the working body, distribute them more evenly and without distortions in the mechanism, and increase the reliability and productivity of the installation. 16
18 Electrical network ED 1 RM ED Fig..4. Multi-motor electric drive A multi-motor electric drive is used in mine hoists, in particular, it was first used in Shepetivka at the end of the 19th century. Electric shaft "an interconnected electric drive that provides synchronous movement of two or more executive bodies of a working machine that do not have a mechanical connection" . Examples include sluice drives and long conveyor lines. Fig..5 shows a diagram of a conveyor on asynchronous EM with a phase rotor, explaining the principle of operation of an electric shaft. The rotational speeds ω 1 and ω, due to the electrical connection of the rotors of the electric motors, will be the same or synchronous. ω 1 conveyor belt ω EM 1 EM electric shaft Fig..5. Illustration of the electric shaft operation
19 EM power range from fractions of a watt to kW, speed control range up to 10,000:1 or more, using both low-speed motors (hundreds of rpm) and high-speed ones (up to rpm). EP is the basis for the automation of technological objects in industry, agriculture, and space; realizing the most important task of our time, increasing labor productivity. Currently, the electric drive is characterized by a tendency to use energy-saving technologies. To traditional systems that allow energy to be returned to the network (this process is called recuperation), such as a generator-motor system (G-D system), an electric cascade (an adjustable electric drive with a IM with a phase rotor, in which slip energy is returned to the electric network), electromechanical cascade (adjustable electric drive with IM with a phase rotor, in which the slip energy is converted into mechanical energy and transferred to the EM shaft), there is a mass replacement of an unregulated electric drive with an adjustable one. As a consequence, the design of the EA becomes gearless, which increases the overall efficiency of the drive. Progress in the design of converter technology, in particular for frequency converters, stimulates the replacement of DC motors and synchronous EMs with cheaper and more reliable asynchronous EMs with a squirrel-cage rotor. If we consider electric propulsion systems from the standpoint of the theory of electric drive, then as an object of study it is an electromechanical system, which is a set of mechanical and electromechanical devices united by common power electrical circuits and (or) control circuits, designed to implement the mechanical movement of the object. In the electric drive, three parts are combined into a single whole (Fig. 6): the mechanical part, the electric motor and the control system. eighteen
20 Email network Email engine M, ω Mech. part Useful mechanical work ECS EMP RD PU IM DOS M mech to DOS ISU from DOS Control system from memory Fig..6. Functional diagram of the electric drive from the point of view of the theory of the electric drive The mechanical part includes all moving elements of the mechanism of the RD motor rotor, the PU transmission device, the IM actuator, to which the useful mechanical moment M mech is transmitted. The electric motor device includes: an electromechanical energy converter EMF, which converts electrical power into mechanical power, and the rotor of the RD engine, which is affected by the electromagnetic torque M of the engine at a rotation frequency (angular velocity) ω. The control system (CS) includes the energy part of the ECS and the information part of the IMS. The ISU receives signals from the master devices of the memory and feedback sensors DOC. 19
21 LECTURE 3 MECHANICAL PART OF THE ELECTRIC DRIVE Issues discussed in the lecture. 1. Purpose and main mechanical components of the EP. Active and reactive static moments. 3. Typical loads of the mechanical part of the electric drive. The main function of the electric drive is to set the working machine in motion in accordance with the requirements of the technological regime. This movement is performed by the mechanical part of the electric drive (MCH EP), which includes the rotor of the electric motor, the transmission device and the working machine (Fig. 3.1). Shown in fig. 3.1 parameters denote M in, M rm, M io moments on the shaft of the engine, working machine, executive body; ω in, ω rm, ω io angular velocities of the EM shaft, working machine, executive body; F io, V io force and linear speed of the executive body. Rotor M in ω in Transfer device M rm ω rm Working machine M io ω io F io V io Fig.3.1. Scheme of the mechanical part of the electric drive Depending on the type of transmission and the designs of the working machine, they distinguish (Fig. 3.1): EP of rotational movement, which provides, respectively, the rotational movement of the executive body RM; output parameters moment IO mechanism M io and angular frequency of rotation ω io; EP of translational motion, which provides translational linear motion of the IO of the working machine; output parameters force F io and linear speed V io.
22 Note that there is also a special ED, called an oscillatory electric drive, which provides reciprocating (vibratory) movement (both angular and linear) of the RM executive body. In the mechanical part of the EP, there are various types of forces, moments, which differ in the nature of the action. Specifically, static moments are reactive M cf and active M ca. Reactive moments are created by the force of friction, the forces of compression, tension, torsion of inelastic bodies. A classic example here is dry friction (Fig. 3.). The friction forces always oppose the movement, and when the electric drive is reversed, the friction moment due to these forces also changes direction, and the function M c (ω) at a speed ω = 0 undergoes a discontinuity. Friction forces are manifested in the gears of the electric motor and working machines. F m V F tr ω F tr V m F M sr M sr M s 3.. Dependence of the static moment of dry friction forces on the speed Active (potential) moments are created by gravity, compression, tension, torsion forces of elastic bodies. In MCH EA, active moments arise in loaded elements (shafts, gears, etc.) during their deformation, since mechanical connections are not absolutely rigid. The features of the action of potential moments are clearly manifested by the example of gravity. When lifting or 1
23 when the load is lowered, the direction of gravity F j remains constant. In other words, when the electric drive is reversed, the direction of the active moment M sa remains unchanged (Fig. 3.3). ω M s VV M sa keeps it constant. Working machines, despite the great variety of designs and operations performed, can be classified according to the type of dependence of the static moment on a number of factors. There are 5 groups of mechanisms on an enlarged basis. The first group includes mechanisms in which the static moment does not depend on the rotation speed, that is, M c (ω) = const. This means that the mechanical characteristic of the working machine, the dependence of the static moment on the rotation frequency is a straight line parallel to the axis of the angular velocity ω, and undergoes a discontinuity at ω = 0 for reactive static moments (as shown in Fig. 3.), For example, for a belt conveyor with uniform linear load. F j m
24 For active Ms (as shown in Fig. 3.3) the mechanical characteristic is independent of the direction of motion. A typical example is the lift mechanism. The second group of mechanisms is quite representative [, 3]. Here, M c depends on the speed of rotation of the RM: () = M + (M + M) Ms c0 sn c0 a ω ωn ω, (3.1) where M from the moment of mechanical friction losses; M SN static moment of the working machine at the rated speed ω n; ω current rotation speed; and the proportionality factor. At a = 0, we have M c (ω) = M cn, that is, we obtain the mechanical characteristic of the machines of the first group. With a = 1, we have a linear dependence of the static torque on the speed, which is inherent, for example, in DC generators G operating at a constant resistance R (Fig. 3.4). ~ U 1, f 1 GR ω M s (ω) U ov OB M s0 M s fans, propellers, centrifugal pumps, and other such mechanisms). 3
25 ~ U 1, f 1 ω М с (ω) М с0 reduces the processing speed of the part ω (Fig. 3.6). М с ~ U 1, f 1 ω V ω М с (ω) The third group of mechanisms is a group of machines in which the static moment is a function of the angle of rotation of the shaft PM α, that is, M c = f(α). This is typical, for example, of connecting rod-crank (Figure 3.7) and eccentric mechanisms, in which the rotational movement with a rotation frequency ω is converted into a reciprocating movement with a speed V. The working stroke of the mechanism, at which 4 M s0 M s is reached
26 is the maximum static moment M cmax, there is, for example, at 0 α π, a reverse motion with a maximum moment at π α π. M cmax, хх ω М s M cmax М s (α) M cmax, хх V М s on the speed of movement, i.e. М с = f(α, ω) A similar dependence is observed when electric transport moves on a rounded section of the track. The fifth group of mechanisms is the RM group, in which the static moment changes randomly in time. It includes geological drilling rigs, coarse crushers and other similar mechanisms (Fig. 3.8). α М с ω М с (t) 0 t
27 LECTURE 4 DC ELECTRIC MACHINES Questions discussed in the lecture. 1. The design of DC machines .. Basic parameters and electromechanical energy conversion in DC machines. 3. Classification of DC motors. 4. Approximate determination of armature resistance. The DC electric machine (MPT) has a specific design. Schematically, using the P-9 electric motor as an example, it is shown in Fig. The fixed part (stator) contains the main poles 1 with coils that form an inductor or excitation system of the machine. The poles are evenly distributed on the inner surface of the frame 3, which combines the functions of the mechanical part (housing) and the active part (yoke of the stator magnetic circuit). Since a constant magnetic flux passes through the frame (yoke), which does not induce eddy currents in it, it is made of monolithic steel. The cores of the main poles are most often made laminated: they consist of individual plates tied together with rivets, studs, or others. Such a design solution is not used to limit eddy currents, but rather is dictated by the convenience of manufacturing the pole. In addition to the excitation windings (OB), the main poles of the MPT can contain a compensation winding designed to compensate for the demagnetizing effect of the armature's own magnetic field (armature reaction), as well as a stabilizing winding used for low-speed high-power motors when it is necessary to temporarily increase the speed by 5 times. To ensure sparkless switching, the machine is provided with additional poles 4, the windings of which are connected in series to the rotor circuit. 6
28 Fig. DC machine type P-9 The MPT rotor is more often called an armature. It carries the main winding of the machine, through which its main current flows. Anchor winding 5 is located in the grooves of the magnetic circuit 6. Conclusions 7
29 windings are connected to the collector plates 7. The magnetic circuit and the collector are placed on a common shaft 8. For normal operation of the DC machine, the grooves of the magnetic circuit must be strictly oriented relative to the plates 7. Collector brushes are pressed against the outer (active) surface of the collector. (coal, graphite, composite, etc.). One group may contain one or more brushes, depending on the current passed through the contact. The contact area is important (it is desirable to provide a fit close to 100%) and the force of pressing the brush to the collector. The brushes are mounted in brush holders that orient and press the brush. The brush holders themselves are placed on special pins of the traverse 9 mounted on the inner side of the bearing shield 10. The traverse can be rotated around the axis of the machine and fixed in any selected position, which allows, if necessary, to adjust the position of the brushes on the collector from the condition of minimal sparking in the brush contact. DC machines are more often used as motors, they have a high starting torque, the ability to widely adjust the speed, are easily reversed, have almost linear control characteristics, and are economical. These advantages of MPT often put them out of competition in drives requiring wide and precise adjustments. An important advantage of MPTs is also the possibility of their regulation by low-current excitation circuits. However, these machines are used only where it is impossible to find an equivalent replacement. This is due to the presence of a brush-collector assembly, which causes most of the shortcomings of the MPT: it increases the cost, reduces the service life, creates radio interference, acoustic noise. Sparking under the brushes accelerates wear on the brushes and commutator plates. Wear products cover the inner cavity 8
30 machine with a thin conductive layer, degrading the insulation of conductive circuits. The operation of the electric motor and DC generator is characterized by the following basic quantities: M is the electromagnetic moment developed by the electric motor, N m; M c the moment of resistance (load, static moment) created by the production mechanism, N m, is usually reduced to the motor shaft (reduction formulas are discussed in lecture 14); I I armature current of the electric motor, A; U voltage applied to the anchor chain, V; E electromotive force (EMF) of a DC machine (for an electric motor it is called counter-emf, since in an electric motor it is directed towards the voltage U and prevents the flow of current), V; F magnetic flux created in the electric motor when the excitation current flows through the OF, Wb; R I armature circuit resistance, Ohm; ω is the angular frequency (speed) of rotation of the EM armature, s -1 (instead of ω, the value n, rpm is often used), 60 ω n =. (4.1) π R motor power, W, distinguish between mechanical (useful) power on the shaft EM R mech and full (electrical) power P mech = M ω, (4.) R el = U I i; (4.3) η efficiency factor of the MPT, equal to the ratio of useful power to total; λ coefficient of overload capacity, distinguish between overload capacity for current λ I and torque λ M: 9
31 λ I \u003d I max / I n; λ M = M max / M n. The relationship between the parameters of the MPT is reflected in the following four formulas: dω MM = c dt J, (4.4) E = K Ф ω, (4.5) UE Ii =, R i (4.6) М = К Ф I i, (4.7) where J is the moment inertia of the electric drive system, kg m; dω/dt angular acceleration of the motor shaft, c -1 ; K is the design constant of the electric motor, pn N K =, (4.8) π a where pn is the number of pairs of main poles; N is the number of active armature conductors; a is the number of pairs of parallel armature branches. Formula (4.4) is a modified record of the basic equation of motion of the electric drive dω M Mc = J. (4.9) dt Note that the basic equation of motion is an analog of Newton's law a = F/m. The only difference is that for rotational motion, linear acceleration is replaced by angular acceleration ε = dω/dt, mass m is replaced by moment of inertia J, and force F is replaced by dynamic moment M dyn, equal to the difference between the moment of the electric motor M and the static moment M s. Formula (4.5) reflects the principle of operation of a DC generator based on the law of electromagnetic induction. In order for the EMF to appear, it is enough to rotate the armature with a certain speed ω in the magnetic flux F. 30
32 EMF E in the machine cannot be obtained if at least one of the quantities is missing: ω (the motor does not rotate) or Ф (the machine is not excited). Formula (4.6) shows that the current I i in the armature circuit flows in the motor under the action of the voltage U applied to the armature. The value of this current is limited by the counter-emf generated during the rotation of the electric motor and the total resistance of the armature circuit. Formula (4.7) actually illustrates the principle of operation of a direct current ED based on the law of interaction of current in a conductor and a magnetic field (Ampère's law). For the occurrence of a torque, it is necessary to create a magnetic flux F and pass the current I I through the armature winding. The above formulas describe all the main processes in a DC motor. MPT is distinguished by the way the winding of the main poles (excitation winding) is included in the electrical circuit. 1. DC machines with independent excitation. The essence of the term is that the electric circuit of the excitation winding (OV) is independent of the power circuit of the EM rotor. For generators, this is the practical only option for a circuit solution, because. the excitation circuit controls the operation of the MPT. Excitation in DC motors with independent excitation (DPT NV) can be performed on permanent magnets. DPT NV with traditional OF have two channels for controlling the rotor voltage and the voltage of the excitation winding. DPT NV are the most popular DC electric machines. Electric motors with parallel excitation (DPT PV). They are characterized by the inclusion of OB in parallel with the ED armature circuit. According to their characteristics, they are close to DPT NV. 3. ED with sequential excitation (DPT Seq.V). The stator winding is connected in series with the rotor winding, which causes the dependence of the magnetic flux on the current.
33 anchors (actually from the load). They have non-linear characteristics and are rarely used in practice. 4. Motors with mixed excitation are a compromise EM with series and parallel excitation. Accordingly, in the ED there are two OBs - parallel and serial. If the value of the resistance of the armature winding is unknown, then an approximate formula can be used. Assuming that half of the power losses are associated with losses in the armature winding copper, we write the formula M U n n η =. n ω I n n n n i; or me. (4.11) In In R U n I R 3
34 LECTURE 5 MECHANICAL AND ELECTROMECHANICAL CHARACTERISTICS OF THE INDEPENDENTLY EXCITED DC MOTOR Issues discussed in the lecture. 1. Natural electromechanical and mechanical characteristics of a DC motor of independent excitation (DPT NV) .. Rigidity of the static characteristic. 3. System of relative units. 4. Mechanical and electromechanical characteristics of DPT NV in relative units. Before proceeding to the consideration of the characteristics of the DPT NV, we give some definitions. The mechanical characteristics (MX) of the engine are the dependences of the steady-state speed on the torque n \u003d f 1 (M) or ω \u003d f (M). The electromechanical characteristics (EMC) of the engine are the dependences of the steady-state speed on the current n \u003d f 3 (I) or ω \u003d f 4 (I). Both MX and EMC can also be represented by inverse functions M = ϕ 1 (n) or I = ϕ 4 (ω). The characteristics are called natural if they are obtained under nominal power conditions (at nominal voltage and speed), nominal excitation and the absence of additional resistances in the armature circuit. Engine characteristics are called artificial when any of the factors listed above are changed. To derive the electromechanical and mechanical characteristics of a DC motor with independent (parallel) excitation, consider the simplest motor switching circuit (Fig. 5.1). 33
35 U + - I E DP KO R add I in OB R DV + U in - Fig Electrical circuit diagram of a DC motor of independent excitation DC mains voltage U c \u003d U is applied to the armature of the electric motor, which in steady state is balanced by EMF (E) motor and voltage drop in the armature circuit (I I R yats). U \u003d E + I R yat, (5.1) where R yat = R i + R add + R dp + R to the total resistance of the armature circuit, Ohm; R I armature winding resistance, Ohm; R additional additional resistance in the armature circuit, Ohm; R dp, R ko respectively, winding resistance of additional poles and compensation winding, Ohm. Insulation class Table 5.1 Operating temperature, С А 105 Е 10 В 130 F 155 Н 180 С node. Bringing the resistance of the windings in the armature circuit
36 to the operating temperature t, C, is carried out according to the following formula: R \u003d R (1 + α θ), (5.) ; α temperature coefficient, (C) -1, for copper 3 usually take α \u003d 4 10 (C) -1; θ is the difference between the operating temperature and t 0, C. The additional resistance in the brush-collector assembly can be taken into account as the ratio of the voltage drop at the brush-collector contact U w = V to the rated armature current. Substituting the value of E into equation (5.1) according to (4.5) and making the appropriate transformations with respect to the rotational speed ω, we obtain the electromechanical characteristic of the DC electric motor of independent (parallel) excitation U I R n U R n ω = = I n. (5.3) Kfn Kfn Kfn Having expressed the value of the armature current through the electromagnetic torque (4.7) and substituting the current value into equation (5.3), we find the mechanical characteristic of a DC motor with independent (parallel) excitation: UR ац ω = M. (5.4) KФ ( ) n KFn Analyzing equations (5.3) and (5.4), we see that mathematically these are the equations of a straight line crossing the velocity axis at the point ω 0. The value ω 0 = U / (K Fn) is called the ideal idle speed, and the ratios R R jac Ib = M = ω c (5.5) KF KF () 35
37 is called a static speed difference relative to ω 0, caused by the presence of a static moment on the motor shaft. The following formula is valid: ω = ω 0 - ω s. (5.6) To construct a natural mechanical characteristic (EMH), it is necessary to find two points. One of them is determined from the passport data of the engine for nominal values n n and M n: ω n = π n n /30 = 0.105 n n, M n = P n / ω n, where P n is the rated power of the engine, W; n n rated speed of EM, rpm. The second point corresponds to the ideal idle when I = 0; M = 0. It can be found from equation (5.3) when substituting the passport data of the engine: Un ω ω n 0 =. (5.7) Un In R I The construction of a natural electromechanical characteristic (EEMH) occurs in a similar way using the passport value of the rated current I n. The EMX can be constructed knowing ω 0 and the slope of the characteristic, which is a straight line. The slope value is determined by the derivative dm/dω = β s, called the static stiffness of the mechanical characteristic (KF) dm β s = =. (5.8) dω R jac In practice, the modulus of static stiffness β = β s is used. The value of β depends on the resistance of the anchor circuit and the excitation magnetic flux. In view of the above, the mechanical characteristic equation can be written as ω = ω 0 M / β. (5.9) 36
38 To compare electric motors different in power, current, torque, number of pole pairs allows the representation of the characteristics of EM in relative units. The system of relative units is quite often used in technical calculations and is based on taking some arbitrary value as the base one. The absolute values of the parameters of the same physical nature k i, referred to the base value of k bases, can be compared with each other. In relative units o k k i i =. (5.10) kbase To analyze the characteristics of a DC motor of independent excitation, we will take for the base values: U n rated voltage; I n rated motor current; M n rated motor torque; ω 0 ideal idle speed; F n nominal magnetic flux. The basic resistance value is usually defined as R base = U n / I n, (5.11) where R base has the following physical meaning - this is the resistance of the armature circuit, which limits the armature current to the nominal value in the inhibited state (ω = 0) and the applied nominal voltage. To express the electromechanical characteristic (5.3) in relative units, it is necessary to divide the right and left sides of the equation by the ideal idle speed ω 0 EEMH. As a result, we obtain the expression o o o U o R yc ω = I, (5.1) o o Ф Ф 37
39 ω where ω o o U o Ф o I o R ац = ; U = ; F = ; I = ; R jac =. ω 0 U n F n I n R base The equation of the mechanical characteristic in relative units can be obtained from equation (5.1) after substituting the expression I = into it, where M =. o o M o M o M F n The natural characteristics of the DPT NV in relative units will take the form: a) electromechanical b) mechanical o o o R yat ω = 1 I, (5.13) o o o ω = 1 M R yat. (5.14) o o with I R o yc M o o yc Static velocity difference ω = = R, o o whence it follows that I = M. Thus, in relative units, the natural mechanical and electromechanical characteristics coincide. When M \u003d M n and I \u003d I n, from equations (5.13) and (5.14) it can be seen that the static drop at rated load is equal to the resistance of the armature circuit in relative units, that is, o \u003d R o ωsn yat. The value of yc depends on the engine power and is within the limits of 0, 0.0 for DPT NV with power from 0.5 to 1000 kW. Knowing the relative resistance of the armature, it is easy to determine the short-circuit current in relative units I k \u003d o Ik I o o o Ik U R Yats n. R o =, in absolute units, this current is 38
40 LECTURE 6 SPEED CONTROL IN A DC MOTOR Questions discussed in the lecture. 1. Artificial electromechanical (IEMH) and mechanical (IMH) characteristics of DCT NV with a change in rotor resistance. Artificial electromechanical and mechanical characteristics of DCT NV with a change in magnetic flux. 3. Artificial electromechanical and mechanical characteristics of DPT NV when the supply voltage changes. Rheostatic speed control is carried out by introducing additional active resistance resistors into the armature circuit, i.e. R jac \u003d (R i + R ya) \u003d var for U \u003d U n, F \u003d F n,. As can be seen from the mechanical characteristic equation (5.4), when varying the value of the additional resistance Rdya in the armature circuit, the ideal idle speed ω 0 remains constant, only the modulus of static stiffness β changes, and with it the stiffness (steepness) of the characteristic (Fig. 6.1) . For example, with the introduction of an additional resistor with a resistance R dya \u003d R i, the static stiffness modulus of the artificial mechanical characteristic (IMC) β and is two times less than for the natural characteristic β e, i.e. β and = 0.5 β e. Accordingly, the static velocity drop ω = ω + ω = ω will double. not R in relative units, the rheostatic mechanical characteristic can be written o o o o o o o ω = 1 M R n = 1 M R n + R n
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S=UIP=Mω
N.I. Usenkov. Electric
sky drive N.I. Usenkov. Electric
sky drive N.I. Usenkov. Electric
sky drive N.I. Usenkov. Electric
sky drive
Introduction
1.1. Definition of the concept "Electricdrive unit"
electric drive
is a controlled electromechanical
system. Its purpose is to convert electrical energy
into mechanical and vice versa and manage this process.
The electric drive has two channels - power and information
(picture
1.1).
By
first
channel
transported
convertible
energy, through the second channel is carried out
energy flow management, as well as the collection and processing of information about
the state and functioning of the system, its diagnostics
faults.
The power channel consists of two parts
electrical and
mechanical and must contain
connecting link
electromechanical converter.
N.I. Usenkov. Electric
sky drive
Figure 1.1. General structure of the electric drive
upper level automated control systemChannels of connection
IP
Net
EP
channel
electric drive
EMF
MP
Worker
organ
Electrical part
Mechanical
Power channel of the electric drive
N.I. Usenkov. Electric
sky drive
Process plant
System
electricity supply
Informational In the electrical part of the power channel of the electric drive
includes electrical converters EP, transmitting
electrical energy from the IP power source to
electromechanical converter EMF and vice versa and
carrying out the transformation of the parameters of the electrical
energy.
Mechanical
part
electric drive
includes
from
moving body of the electromechanical converter,
mechanical gears MP and the working body of the installation, in
in which mechanical energy is usefully realized.
electric drive
interacts
from
system
power supply (or source of electrical energy),
technological installation and through information
IP converter with information system more than
high level.
Electric
drive unit
used
in
economy.
wide
Spread
electric drive
N.I. Usenkov. Electric
conditioned
features
electrical
energy:
sky drive Electric drive is one of the most energy-intensive
consumers and energy converters. He consumes
more than 60% of all electricity produced.
Electric
drive unit
wide
used
in
industry, transport and public utilities
economy.
Electric
drive unit
one
from
most
energy-intensive consumers and energy converters.
Theory
regulated
electric drive
received
intensive development thanks to
improvements
traditional and the creation of new power controlled
semiconductor devices (diodes, transistors and
thyristors), integrated circuits, development of digital
information technology and development of various
microprocessor control systems.
Ownership
theory
in
areas
regulated
electric drive
is an
one
from
the most important
component of professional training of specialists
N.I. Usenkov. Electric
direction "Electrical engineering,
energy and technology
sky drive
1.2. Composition and functions of the electric drive
Functionelectric
converter
EP
includes
in
conversion of electrical energy supplied by network C and
characterized by voltage Uc and current Ic of the network, into the electrical
the same energy required by the engine and characterized by the quantities
U, I.
Converters are unmanaged and managed. They are
may have one-sided (rectifiers) or two-sided (with
availability
two
kits
valves)
conductivity,
At
one-way conduction of the transducer and reverse (from
load) energy flow uses an additional key
element on the transistor for "draining" energy in braking mode
electric drive.
EMI electromechanical converter (motor), always
present in the drive converts the electrical
energy (U, I) into mechanical energy (M,ω).
Mechanical transducer MP (transmission): gearbox, pair
screw nut, N.I.
blocks,
Usenkov.crank
Electric crank mechanism
coordinate
moment M and speed ω of the engine with
sky drive Figure 1.2. Energy channel of the electric drive
P2
P1
Net
ΔPс
ΔPe
Us, I s
∆Pr
ΔPm
ΔPem
U, I
Mm, ω m
M, w
EMF
EP
Δ Pro
MP
∆Pr
N.I. Usenkov. Electric
sky drive
RO quantities,
characterizing
convertible
energy:
voltages, currents moments (forces) speeds shaft position in
space are called the coordinates of the drive.
The main function of the actuator is to control
coordinates, that is, in their forced directional
change in accordance with the requirements of technological
process.
Coordinates must be managed within,
allowed
structures
elements
electric drive,
how
ensure the reliability of the system. These allowable
limits are usually associated with the nominal values of the coordinates,
ensuring optimum use of the equipment.
N.I. Usenkov. Electric
sky drive automated
electric drive
(AEP)
this
electromechanical system consisting of electrical
EM machine connected by mechanical transmission
PU with working mechanism RM, power converter SP,
SU control system, BSU sensor unit,
which act as feedback sensors
main
variables
states
EP
(parameters:
shaft position of the working machine, angular velocity, moment,
motor current) and power supplies providing
power supply of the specified electrical devices.
Semiconductor
joint venture
serve
for
harmonization
electrical
parameters
source
electrical
energy
(voltage,
frequency)
from
electric
parameters of the EM machine and regulation of its parameters
(speed, voltage and reversal of rotation
N.I. Usenkov. Electric
sky drive Figure 1.3. Block diagram of automated
electric drive
Source of power
Signal
tasks
EM
SU
joint venture
BSU
PU
RM
EP information channel
Electric part of EP
N.I. Usenkov. Electric
sky drive
Mechanical part of EP The control system is designed to control
power converter and is built, as a rule, on
chips or microprocessor. At system input
management
served
signal
tasks
And
signals
negative feedback from the sensor unit
devices.
System
management,
in
accordance
from
algorithm embedded in it, generates signals
power converter control, controlling
electrical machine.
Most
perfect
electric drive
is an
automated
electric drive
adjustable
electric drive
from
automatic
regulation
state variables.
N.I. Usenkov. Electric
sky drive The automated electric drive is divided into:
Speed or torque stabilized EP;
Software-controlled EP that moves
working mechanism in accordance with the program included in the signal
tasks;
Follower EA, which moves the working mechanism in
according to arbitrarily changing input signal
Positional
EP,
designed
regulation of the position of the working mechanism
N.I. Usenkov. Electric
sky drive
for N.I. Usenkov. Electric
sky drive Electric drive based on DC motors
current
used
in
various
industries
industry:
metallurgy,
engineering,
chemical, coal, woodworking, etc.
Regulation
angular
speed
engines
permanent
current
takes
important
a place
in
automated electric drive. Application with
this purpose of thyristor converters is
one of the modern ways to create a regulated
DC electric drive.
N.I. Usenkov. Electric
sky drive The speed control of the DPT with HB is carried out by three
ways:
1. Changing the voltage at the armature of the motor with a constant current in the winding
arousal;
2. By changing the current in the motor excitation winding at a constant
anchor voltage;
3.Combined motor armature voltage change
excitation winding.
and current in
The armature voltage of the motor or the current in the field winding is changed from
using controlled rectifiers, of which the largest application
received single-phase and three-phase bridge rectifiers.
When controlling the motor through the field winding circuit, the controlled
the rectifier is made for lower power and has better weight, size and cost indicators.
N.I. Usenkov. Electric
sky drive However, due to the large time constant
excitation windings, the electric drive has the worst
dynamic
properties
(is an
less
high-speed) than on the motor armature circuit. So
the way
choice
chains
management
determined
specific drive requirements.
When working with production mechanisms
(e.g. main and auxiliary mechanisms
gears in processing machines, crane mechanisms,
elevators) it is necessary to change the direction of rotation
engine
(realize
reverse).
Change
directions of rotation are usually accompanied by such
requirements like fast (and at the same time smooth)
braking and smooth acceleration.
N.I. Usenkov. Electric
sky drive Reversal of the direction of rotation of the drive motor can be achieved
by changing the polarity of the voltage supplied to the armature or by changing
direction of current in the excitation winding. For this purpose, in the anchor chain or
excitation windings enter a contact switch (reverser) or
two controlled thyristor converters are used.
Structural diagram of a reversible thyristor converter with
contact switch in the armature winding circuit is shown in the figure. IN
this circuit, as in most converters designed for
drive, rectifying mode alternates with inverting mode.
So, for example, when accelerating in the start mode and stabilizing it in
conditions
raise
loads
on the
shaft
engine
thyristor
the converter operates in rectification mode, supplying energy
engine. If necessary, braking and subsequent stop
engine energy supply to it from the network through the converter
stop,
N.I. Usenkov. Electric
sky drive translating
motor in invert mode.
DC machine under the action of inertial
mass on its shaft goes into generator mode,
returning the stored energy through the converter
to the AC mains (regenerative braking).
Reversing Converter Block Diagram
Net
380 V, 50 Hz
Usync
VS1
UZ1
VS6
SIFU
Uо.с
1
ID1
2
QS1
Uda
1
2
ID2
M1
LM1
N.I. Usenkov. Electric
sky drive
Uz.s N.I. Usenkov. Electric
sky drive
Thyristor converter-motor system
The main type of converters used in regulatedDC EPs are semiconductor static
converters (transistor and thyristor). They represent
controlled reversing or non-reversing rectifiers,
collected on zero or bridge single-phase or three-phase
schemes. Power transistors are mainly used for
pulse voltage regulation in low power EP.
The principle of operation, properties and characteristics of the TP - D system
Consider the example of the circuit shown in Fig. 2.
N.I. Usenkov. Electric
sky drive à)
á)
~ U1
i1
T1
e2.1
VS1
Ud
+
M2
+
Ia1
ID
Uo1
Uo
2
e2.2
LM
3
VS2
I
0
L
1
Ia2
4
5
6
Uo2
Ñ È Ô Ó
UÑ
Picture
2
N.I. Usenkov.
Electric
sky drive
7
M Controlled rectifier (converter) includes
matching transformer T, having two secondary windings,
two thyristors VS1 and VS2, smoothing reactor with
inductance L and a pulse-phase control system
SIFU. The excitation winding of the OBM motor is powered by its own
source.
The rectifier provides voltage regulation on
motor by changing the average value of its EMF EP. This
is achieved with the help of SIFU, which, at the signal UU, changes
thyristor control angle α (opening delay angle
thyristors VS1 and VS2 relative to the moment when the potential on
their anodes becomes positive compared to
potential at the cathode). When α = 0, i.e. thyristors VS1 and VS2
receive control impulses Uα from the SIFU at a specified moment,
the converter performs full-wave rectification
and full voltage is applied to the armature of the motor. If with
using the SIFU, the supply of control pulses to the thyristors VS1 and
VS2 occurs with a shift (delay) by an angle α ≠ 0, then the EMF
converter decreases, and consequently decreases
average voltage supplied to the motor.
N.I. Usenkov. Electric
sky drive The dependence of the average value of the EMF of a multi-phase converter
from the thyristor control angle a has the form:
(1)
ECP Emax m sin m cos ECP 0 cos
where m is the number of phases;
E - amplitude value of the EMF of the converter;
ESR0 - converter EMF at α = 0.
To reduce the detrimental effect of current ripple on the armature target
a smoothing reactor is usually switched on, the inductance L of which
is selected depending on the allowable current ripple level.
Equations for electromechanical and mechanical characteristics
engine:
(2)
(3)
ECP 0 cos k I RY RP k
ECP 0 cos
k M RЯ
RP
k2
where
- equivalent resistance
RP xT m 2 RT RL
converter;
xT, RT - respectively reduced to the secondary winding
leakage inductive reactance and active resistance
transformer windings;
RL is the active resistance of the smoothing reactor.
N.I. Usenkov. Electric
sky drive In the shaded area, the engine is running in the mode
intermittent current, which determines a noticeable change (decrease)
stiffness characteristics. Due to one-way conduction
transducer characteristics are located only in the first
(1...3 at α = 0; 30, 60°) and fourth (4...7 at α = 90, 120, 150, 180°)
quadrants. Smaller control angles correspond to a larger SP and,
hence higher engine speed; at α = π/2 EMF
UV EP = 0 and the engine operates in dynamic braking mode.
On fig. 3 shows a diagram of an EA with a three-phase bridge
irreversible UV.
N.I. Usenkov. Electric
sky drive ~ 380 Â; 50 Ãö
T1
UÑ
Uo
Ñ
È
Ô
Ó
U
VS1
+
VS6
VS1
VS4
VS3
VS6
VS5
VS2
Ud
L
ID
M1
+
LM
-
UB
N.I. Usenkov.
Electric
Picture
3
sky drive
-For engine performance in all four
quadrants are used reversible controlled rectifiers,
which consist of two non-reversible rectifiers, for example with
zero output fig. 4.
but)
~ 380 V; 50 Hz
b)
T1
2
UC
U
U
FROM
AND
F
At
VS1
+
VS6
VS1
VS4
VS3
VS6
VS5
VS2
L1
-
2
L
1 min
0
min
M
1 2
1max
M1
UB
2 2
L2
+
max
-
N.I. Usenkov.
Electric
Picture
4
sky drive Reversible
called
converters,
allowing
change the polarity of the DC voltage and current in the load.
Reversible SW uses two basic principles
valve sets control: joint and separate.
Joint control provides for supply from the system
pulse-phase control of thyristors control pulses
Uα simultaneously on thyristors of both sets - VS1, VS3, VS5
(cathode group) and VS2, VS4, VS6 (anode group). At the same time, due to
the presence of a shift angle between the control pulses of two sets
thyristors close to π, one of them works in a rectifier
mode and conducts current, and the other, working in inverter mode, the current
does not conduct. To ensure such control between the average
EMF values of the rectifier and inverter must exist
ratio
, however, due to the difference of instantaneous values
EMF between sets of thyristors flows the so-called
balancing current. To limit it in the circuit shown in Fig.
4a, surge reactors L1 and L2 are provided.
N.I. Usenkov. Electric
sky drive Schemes of valve converters,
providing direction change
energy flow
In automated electric drives
adjust the speed of the drive motor.
required
When using DC machines, there is
the task is not only to control the speed of rotation, (for
by changing the magnitude of the supply voltage), but also
change of direction of rotation (reverse). For this
need to change both the polarity of the voltage on
load, and the direction of the current in the load.
This problem is solved with a special
DC converter without application
contact equipment,
so-called reverse
N.I. Usenkov. Electric
dc converter
current, consisting
sky drive consisting of two sets of valves, each of which
allows current to flow through the load in only one
direction.
All existing schemes of reversing valve converters
can be divided into two classes:
cross ("eight") schemes and
counter-parallel circuits.
In cross circuits (figure a - zero and b - bridge)
the transformer has two groups of insulated valve windings,
from which two sets of valves are fed.
In back-to-back circuits (figure c), only one
group of valve windings of the transformer.
In reverse
are:
converters
most
three-phase zero;
double three-phase with equalizing
reactor and
N.I. Usenkov. Electric
sky drive
widespread Three-phase reversing converter
with zero output
A
T1
C
Usync
N
a
UZ1
B
b1
1
c1
a2
b
c2
2
Iur2
Lur1
ID1
Uda
Iur2
VS1…
VS3
US2
Lur2
ID2
M1
N.I. Usenkov. Electric
LM1
sky drive
VS4…
VS6
SIFU 1
SIFU 2
Usync
Uzs Three-phase rectifier circuits are used for inductive
load to power the excitation windings of electrical machines,
six-phase
to power the anchor chains of the engine,
twelve-phase especially powerful electric drives.
Operation of the reversing converter
Let us assume that at the initial moment of time the machine
rotated clockwise at a speed of n rpm. At the same time, she
developed back-EMF Ejak and current I flowed through the anchor circuit
(picture
). The machine was powered from the first
converter valve kit UZ1 operating in
rectifying mode. To reduce rotation speed
machine, it is necessary to reduce the supply voltage supplied to it, then
there is a need to increase the thyristor control angle
VS1,VS2,VS3 of UZ1 rectifier.
N.I. Usenkov. Electric
sky drive At the same time, due to the inertia of the engine, its back-EMF Ejak cannot
changes sharply and turns out to be greater than the voltage Ud1 on
outlet
converter
(on the
anchor
engine).
valves
converter UZ1 quickly shuts down and the load current is reduced
down to zero. But on the clamps of the anchor chain of the electric machine,
rotating by inertia, the back-EMF Eyak is preserved, which
allows useful use of the kinetic energy of the rotating
drive, converting it into electric, and at the same time quickly
slow down the electric car.
To do this, you need to convert the first valve kit to
inverter mode, i.e. increase the angle α1 > 90°. But first
converter kit UZ1 cannot be used in inverter
mode, as it is necessary to have reverse polarity on the machine
voltage Ud1. Therefore, the second
valve set UZ2 (α2 > 90°), the outlet of which is connected to
load parallel to the output of the first set UZ1. A car
operates in generator mode, so its rotation speed
falls. Consequently, the back-EMF Eyak, which is
supply voltage N.I.
for Usenkov.
second Electric
UZ2 kit operating in
inverter mode. sky drive n
Braking
Engine e
Overclocking
mode
Engine
mode
0
t
Reverse
I
E
0
t
<90
US2
IN
AND
>90
AND
>90
<90
UZ1
IN
UZ1
<90
IN
Fig 1.2. Operating mode diagram
DC electrical machine
N.I. Usenkov. Electric
sky drive When the electric machine stops (Ejak=0; n=0), you can
convert the second set of UZ2 valves into a rectifier
mode (α2<90°). При этом электрическая машина опять переходит
into engine mode and is powered by a second set of valves
US2.
Direction
rotation
cars
changes
on the
opposite (engine reverse) and she starts again
accelerate (from n=0 to a given speed, for example, to
n=nnom in the third quadrant of the drive coordinates: n and I or n
and M).
If a reverse is required again, then the
angle α2 of the second set of valves UZ2, its valves are closed.
The first set of valves UZ1 is converted to inverter
mode (α 1>90°), the direction of the armature current Id is reversed,
the electric machine operates in generator mode until
complete stop of the engine.
In the future, with a decrease in the angle α1> 90°, the first set
valves UZ1 is switched to rectifier mode and
the engine is accelerated to the set speed.
N.I. Usenkov. Electric
sky drive Regulating characteristic of the reversible
converter
Uda
Ud0
Udα1
α1
Mode
rectifier
0
Udβ1
π
π/2
Mode
inverter
α2
β1
-Ud0
Udβ
N.I. Usenkov. Electric
sky drive
α
β If the average values of stresses on
output UZ1 and UZ2 we get the expression
Udocosα1 = Udocosβ2.
Therefore, it is necessary that α1= β2. Since at
inverter mode β =180°- α, then the equality condition
average voltage values in the equalizing circuit
can be represented as α1+ α2 =180°, where α1 and α2 are angles
control of thyristors of the first and second sets
valves, counted from the point of natural
unlocking thyristors.
N.I. Usenkov. Electric
sky drive External characteristics of the reversible
converter
External characteristics of rectifier and inverter
sets in this case are a continuation of one
another and give a linear resulting outer
characteristics of the reversing converter
Uda
β1
α1
β1 > β
2
α2 > α
β3 > β
2
1
α3 > α
2
Mode
inverter
Mode
rectifier
0
N.I. Usenkov. Electric
sky drive
ID Joint control of valve
kits
If control pulses are applied simultaneously to
valves of both sets UZ1 and UZ2, and control angles
thyristors meet the condition
α1 + α2 = π,
control
valve
agreed.
groups
N.I. Usenkov. Electric
sky drive
called Separate valve control
kits
In order to get an electric drive that works in all four
quadrants of the field: ω - I or ω - M, it is necessary to use a reverse
thyristor converter providing armature current flow
motor in both directions.
Reversing converters contain two groups of thyristors,
connected in opposite parallel to each other.
In this scheme, two valve sets UZ1 and UZ2, each assembled according to
three-phase bridge circuit, connected in parallel with each other with
opposite polarity on the rectified current side.
Apply unlocking pulses simultaneously to both groups of thyristors
not possible, as a short circuit will occur. Therefore, in this scheme
can only work
N.I. Usenkov. Electric
sky drive one group of thyristors UZ1 or UZ2; another group
thyristors must be closed (opening pulses
removed).
Thus, reverse converters with
separate control - these are converters, in
which control pulses come to only one
from sets of valves that conduct current. impulses
control to the second set of valves at this time is not
are supplied and its valves are closed. Reactor Lur in the scheme
may be missing. See Gorby243s
With separate control of the valves, the
only that group of thyristors, which is currently
must conduct current in the load. Selecting this group
depends on the direction of movement of the actuator ("Forward" or
"Back") and from the operating mode of the drive: motor
mode or regenerative braking.
N.I. Usenkov. Electric
sky drive Table 1 - Valve kit selection
EP operation mode
Motor
Brake
Direction
movements
"Forward"
UZ1
US2
"Back"
US2
UZ1
In EA control systems, the selection and inclusion of the desired group
thyristors is produced automatically by means of a logical
switching device of LPU, the construction principle of which
shown in the figure.
N.I. Usenkov. Electric
sky drive We accept the direction of the armature current when working "Forward" in
motor mode for positive. With a positive signal
setting the speed ωset, corresponding to the movement
"Forward" and
speed error signal, which in motor mode is also
will be (ωset- ω)≥0, the signal coming to the LPU from the current regulator,
will have a (+) sign. In accordance with this, the health facility will turn on the electronic
key QS1, which supplies unlocking pulses to the thyristor
group UZ1. Control angle α1 is set by the system
automatic regulation according to the output signal
current regulator RT. Both SIFUs (1) and (2) work in concert so that
what is the sum of the angles sum
α1 + α2 = π .
(1)
Thus, for a thyristor group operating in
rectifying mode, triggering pulses are applied with an angle α1 =
0…π/2. At the same time, SIFU2 generates impulses
N.I. Usenkov. Electric
sky drive control angle α2 = π - α1, i.e. control angle,
relevant
inverter
regime
work
converter UZ2. However, since the electronic key
QS2 is open, control pulses to thyristors of the group
UZ2 are not received.
The UZ2 converter is closed, but
prepared for operation in inverter mode.
Such
principle
agreed
management
valve kits, defined by (1), allows
match the mechanical characteristics of the drive to
motor and braking modes, as shown in
figure.
At
need
braking
drive
the speed reference signal ωset decreases. Error by
speed changes sign (ωass - ω)<0, и на входе ЛПУ знак
signal changes from (+) to (-), according to which
N.I. Usenkov. Electric
sky drive Contact QS1 turns off and contact QS2 turns on. but
switching on contact QS2 does not occur immediately, but with some
the time delay required for the armature current to
decreased to zero and the UZ1 thyristors restored the blocking
properties. The current drop to zero is controlled by the current sensor DT and
null-organ BUT (in other schemes, for this purpose,
valve conductivity sensors).
When the current drops to zero, after a certain delay
time, the QS2 key is turned on and the converter starts working
UZ2, already prepared for operation in inverter mode. Drive unit
enters regenerative braking mode, total time
switching thyristor groups is 5 - 10 ms, which is
acceptable to ensure high quality of ES control.
When working in the motor mode in the "Back" direction, the sign
speed reference is negative and the absolute value
N.I. Usenkov. Electric
sky drive speed errors |ωset - ω | positive, so
the LPU input receives a negative signal, and turns on
key
QS2.
Working
converter
US2
in
rectifying mode. Logical rules of work
LPU are illustrated in Table 2.
Other schemes of health care facilities are also being used.
Mechanical characteristics of the reverse drive TP-D
with separate control are shown in the figure.
With continuous current
are described by equation (1).
anchors
engine
they
In the mode of discontinuous currents in the region of small
torque values, the linearity of the characteristics is violated.
In modern current and speed closed systems
regulation, thanks to the use of adaptive
controllers, it is possible to linearize the mechanical
characteristics of EP iN.I.
priUsenkov.
small electric
moment values.
sky drive Table 2 - The logic of the work of the medical facility
Sign
Sign
Sign
Switched on
Working
Mode
ωass
|ωass- ω|
at the entrance
key
work
health care facility
QS
convert
eh
+
+
+
QS1
UZ1
+
-
QS2
US2
-
+
-
QS2
US2
-
-
+
QS1
UZ1
N.I. Usenkov. Electric
sky drive
electric drive
but
Motor
th
Brake
Motor
th
Brake External characteristic of the rectifier
Uda
Ud0
Ud1
0
ID
I d1
I k.z
N.I. Usenkov. Electric
sky drive
7. Electric drive and automation of industrial installations and technological complexes
Technical implementationN.I. Usenkov. Electric
sky drive N.I. Usenkov. Electric
sky drive N.I. Usenkov. Electric
sky drive Task 1. Determine the values of the reduced moments J and Ms at
lifting the load (Figure 1), if it is known: Jd = 3.2 kg m2; Jr.o.=3.6 kg m2;
gear ratio of the gearbox p=0.96; Efficiency of the executive body
(drum) B=0.94; angular velocity of the engine ω=112 rad/s; speed
lifting load v=0.2 m/s; cargo mass m=1000 kg.
Explanation.
Reduced static moment:
Mc
F p . o. p . o.
p B D
m g p.o.
p B D
1000 9,81 0,2
19.41Hm
0,96 0,94 112
Reduced moment of inertia J:
J
J D J po
i p2
m(
2 3,2 3,6
0,2 2
1000
) 3.3 kg m2.
2
D
112
6,14
N.I. Usenkov. Electric
sky drive Jd, np, ip, p
M, d, Jd
D
PU
Mpo, po, jpo
RO (b), and scheme 3. Familiarize yourself with
MatLab7/Simulink3.
library
major
blocks
in
program
4. Compile a block model of a laboratory setup for carrying out
research in accordance with the given topic and give a brief description
used functional devices and virtual measuring
appliances.
5. Explore the virtual laboratory setup and enter the initial
data in the dialog boxes of the program. Formulate a plan
experiment.
6. After completing the work, draw up a report on the structure:
The title of the work and the purpose of the work;
Description of the laboratory stand;
Analysis of oscillograms of experimental dependencies;
Conclusions.
N.I. Usenkov. Electric
sky drive Work No. N. Research of the electric drive according to
structure "Rectifier-converter-synchronous motor"
Block model of an electric drive with an asynchronous motor
N.I. Usenkov. Electric
sky drive Simulation results
N.I. Usenkov. Electric
sky drive N.I. Usenkov. Electric
sky drive
MINISTRY OF EDUCATION AND SCIENCE
RUSSIAN FEDERATION
FEDERAL AGENCY FOR EDUCATION
STATE EDUCATIONAL INSTITUTION
HIGHER PROFESSIONAL EDUCATION
UFIMSKY STATE OIL
TECHNICAL UNIVERSITY
V.I.BABAKIN
Course of lectures on discipline:
"Automated electric drive of standard
production mechanisms and technological
complexes."
Part 2.
Ufa 2007
1.AED with asynchronous motor 4
1.1AEP with IM with rheostat control 4
1.2AEP with AKZD with adjustable voltage supplied to the stator AD 5
2. Current state of AED with AC motors 7
2.1Problems of synthesis and control of AED 7
3.Automated asynchronous electric drive using synchronous
Electric machine frequency converters 9
4. Automated asynchronous electric drive using asynchronous
Electric machine frequency converters 11
5.Automated electric drive with AC motor with static frequency converters (SFC) 11
5.1 Frequency converter with DC link 12
13
7. AEPT with PE having a controlled rectifier in the structure………………………… .14
8. Speed control in AED with FC with UV………………………………………………… ...17
9.Start in AED with FC with SW……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
10. Braking in AED with SW……………………………………………………………………..19
10.1.Reverse power braking (RT)………………………………………………… ..19
10.2.Dynamic braking………………………………………………………………… 19
10.3.Reverse……………………………………………………………………………………. ..twenty
11. Advantages and disadvantages of AED with FC with SW……………………………………………… .20
12. Automated electric drive using an inverter with WIDE……………………….20
13. Speed regulation, start-up braking in AED with WID…………………………… ...21
13.1 Speed control in AED with WID………………………………………………… …21
13.2 Start-up in the AED with SHIRD……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
13.3 Braking in AED with SHIR………………………………………………………………… 22
14 Automated electric drive using a PWM inverter…………………...22
15 The principle of operation of the inverter with PWM………………………………………………………………..23
16 Schematic diagrams of the inverter with PWM…………………………………………………………24
17 FC with PWM based on non-lockable thyristors……………………………………………....25
18 Element base of modern frequency converters…………………………....26
18.1 Power filters……………………………………………………………………………27
18.2Characteristics of modern powerful power switches with double-sided heat sink
19 Principal diagrams of inverters based on IGBT transistors………………………………...29
20 Speed control in AED with FC with PWM……………………………………………….29
21 Starting in AED with FC with PWM……………………………………………………………………..29
22 Braking in AED with PWM inverter………………………………………………………… .29
23 Emergency modes in AED with FC with PWM……………………………………………………29
24 Influence of the length of the mounting cable on the overvoltage at the motor terminals……….30
25 Principles and fundamentals of vector control……………………………………………...34
26 Realization of vector control…………………………………………………………..36
27 Automated AC electric drive with direct conversion
Frequency vane (LFC)…………………………………………………………………… ..38
28 Automated AC drive in cascade circuits………….40
29 Automated electric drives with electric motor cascades…………………………………………………………………………………………… 42
30 Automated electric drives with electromechanical electromachine cascades…………………………………………………………………………………………..43
31 Automated electric drives with asynchronous valve stages (AVK).44
32 Automated AC drives with dual-feed machines
Niya……………………………………………………………………………………………. .45
33 Automated AC drives with dual power machines in synchronous mode……………………………………………………………………… 46
34 Automated AC drives with dual-feed machines
Niya in asynchronous mode……………………………………………………………………..48
35 Automated AC electric drives with a brushless motor …50
36 Automated servo AC drives……… …….52
1. AED with asynchronous motor
1.1 AED with IM with rheostatic regulation.
These schemes are used for IM with a phase rotor.
Operating principle: By changing the active resistance of the rotor circuit, we thereby affect the slip, while changing the angular velocity. 
One of the most important indicators of the quality of regulation is smoothness. In this case, it depends on the number of steps of the additional resistance introduced into the rotor circuit, which, in turn, is limited by standard control equipment using relay-contactor circuits. An increase in the number of stages will entail an increase in the number of relays and contacts, which in turn will lead to a decrease in the speed and reliability of the system as a whole. In addition, such electric drives have low energy performance, low efficiency in the field of deep regulation, with a significant increase in additional resistance, the stiffness of the characteristic sharply decreases, which will affect the stability of the electric drive.
In order to increase the smoothness of regulation, pulse parametric regulation is used. The essence of this method lies in the alternate introduction and removal of additional resistance in the rotor circuit, while the average value is equal to:
where t 1 - the duration of the closed state of the key;
T 2 - the duration of the open state of the key.
fig.2
ω will change smoothly in the aisle between two boundary characteristics ε=1 and ε=0
The range of speed control in an EA with rheostat control is limited to:
Large power losses (low efficiency)
Low stability (D=1.5÷1).
The principle of operation of such electric drives is that when the voltage supplied to the stator decreases in proportion to the square of the voltage, the electromagnetic torque decreases and the rotation speed ω decreases.
Regulation is carried out using voltage regulators included in the stator circuit. There are two types of regulation:
impulse;
continuous.
Until recently, impulse control methods were mainly used.
The simplest circuit diagram of impulse control: 
fig.3
In this case, the frequency of closures and openings is commensurate with the frequency of the network f
≤ 200 Hz. When the duty cycle of the control pulses changes, the effective voltage value changes: 
When ε=1, the engine operates on a natural mechanical characteristic, while the keys K are constantly closed. As ε decreases, the angular velocity decreases. In this case, the critical moment M CR decreases, as a result, a decrease in the overload capacity (rigidity) of the working part of the mechanical characteristic. At small values of the duty cycle, i.e. at low speeds, the drive is unstable.
Disadvantages:
Low energy performance, which is associated with an increase in voltage and speed, as well as with transient electromagnetic processes caused by turning the motor stator windings on and off.
Such electric drives can only work in a continuous mode, because. do not provide short-term start and stop of the engine.
KN turns on at the intervals of the switched off state of the keys KV, at ε=0 pulses controlling the keys KV. EA will operate in the anti-switch braking mode. The family of mechanical characteristics in such EA will be more rigid in the working part (overload capacity is lower).
The difference between the mechanical characteristics in pulsed voltage regulation and pulsed phase alternation (in the working part, the electric drive operates more stably). At very small values of ε, the characteristics go into the region of braking by counter-wiring, which makes it possible to quickly stop the engine. Such electric drives are for intermittent modes, but these electric drives have even lower energy performance, tk. the imposition of motor and braking modes causes almost continuous electromagnetic transients, accompanied by large power losses.
Disadvantages:
Reducing the supply voltage at constant power on the motor shaft will lead to a decrease in the voltage at the rotor terminals, an increase in the rotor current, a decrease in the power factor of the motor and a decrease in efficiency.
Quality indicators:
Low energy performance;
Low regulation stability:
Control range D=1.5÷1;
Smoothness is high;
Direction single link “down”;
Currently, EPs with continuous voltage regulation are widely used:
RN-AD;
TRN-AD.
Recently, such electric drives have received unreasonably wide advertising. It is proposed to use them for mechanisms operating in a repeated short-term mode. The regulation of ω in the TRN-IM system is carried out by changing the voltage at the stator terminal by changing the firing angle of the thyristors. Fig.5
^
Advantages of EP according to the TRN-AD system:
In terms of initial costs, it is 30-40% cheaper than an EP with a frequency converter; maintenance costs are reduced by 20-50%.
^ Disadvantages of EP according to the TRN-AD system: Low control range D=2÷1.
This disadvantage can be eliminated to some extent by using AED with adjustable EMF in the stator winding, i.e. not voltage regulation, but EMF.
^ 2. Current state of AED with AC motors.
2.1 Problems of synthesis and control of AED.
Control object -
ED (electromechanical converter);
SP (power electrical converter);
IP (measuring transducer).
1) ED(electromechanical converter).
The widest class of electric motors used in a modern AKZD electric drive for general industrial purposes. These motors are designed for use in variable speed drives, for direct connection to an industrial network. Basically, changes in this area are in the nature of some design improvements in the electric motor. Special modifications of AKZD are being developed and mass-produced, intended for use in a frequency-controlled electric drive (by Siemens, AKZD has been developed and mass-produced for five years for use at low and high supply frequencies of 500-1000 Hz). In addition, there is an increase in the production of LEDs with excitation from permanent magnets (contactless). These electric motors have improved weight, size and price indicators, and are not inferior in terms of technical and energy indicators. Among the promising EMs is an inductor motor, which, according to the developers, has much better technical and energy characteristics and requires a very simple power converter (the cost of the electric drive is much lower). A synchronous reluctance electric motor has weight and size indicators that are in the interval between IM and SM, and at the same time, significantly higher energy efficiency at a much lower cost.
2) SP(power electrical converter);
In the field of SP in an electric drive with DC motors, converters with the structure of a rectifier - AVI are currently mainly used. Moreover, if before 2000 the requirements for the quality of rectification were not regulated, then at present a number of regulatory documents have appeared that strictly regulate the presence of rectifier devices in the structure of the joint venture. These are IEEE-519, IEC555 standards - integration standards; GOST 13109. To improve the quality indicators of modern joint ventures, in particular, to improve the quality of power consumption, namely, to increase the power factor, rectifiers on fully controlled power switches with output voltage stabilization are currently used. Circuits with additional inductance, circuits with a switching input key are implemented using smart technology. However, SPs with uncontrolled rectifiers seem to be more efficient and cheaper. The JV currently uses a modern base that uses modern electronic devices such as MGT or IGST thyristors, as well as fully controlled IGBT transistors. In addition, transistors with a voltage resolution of 6-10 kV are currently being developed.
Currently, the most promising operating mode of the SP is the high-frequency PWM mode with a modulation frequency of 20 kHz and vector control (influence through the torque-forming and flux-forming component of the stator current). This mode is the most favorable for motors with a nominal frequency of 500-1000 Hz. in this case, the problem of matching the modulation frequency with the frequency of the voltage supplying the motor is solved much easier. At present, a promising type of joint venture is also NFC, which has a matrix structure with a matrix control system. The advantage of such converters is the absence of reactive elements, i.e. capacitances and inductances in the power circuit, almost sinusoidal shape of the output voltage and current, as well as the ability to work in the leading cosφ mode.
3) IP(measuring transducer).
Traditionally known means are currently used as primary meters, which include commercially available current and voltage sensors, Hall sensors, tachogenerators, photopulse and code displacement and position sensors, electromagnetic revolvers, selsyns, etc. The volume of use of such modern sensors as capacitive, laser is practically equal to zero. The most promising type of IP are indirect meters, in which, based on easily measured parameters, such as active and inductive resistance of the motor, speed and position of the rotor, etc. When using such measuring systems, there is no need to use a large number of sensors and in particular a rotation speed sensor. Such measurement systems are called sensorless.
^
Electric drive control tasks:
The most common type of control problems is the problem of direct control of the EA rotation speed. In addition, there are specially controlled drives that perform the tasks of regulating the electromagnetic torque, power, acceleration, regulating the position of the rotor, and regulating any technological parameter. In addition, there are tasks of stabilization, tracking, positioning, ensuring invariance (is to ensure independence or weak dependence on uncontrolled disturbances), ensuring autonomy (ensuring the independence of any object parameter from other parameters).
Synthesis of ED control is reduced to finding a sufficiently conditioned ED model, which currently in most cases is a system of Kirchhoff equations according to the second law of Ele of electromagnetic circuits of ED and SP. Usually these equations are written for an equivalent two-phase machine, as well as a system of Newton's equations for mechanical circuits of an EP.
The main problem when creating an EP model:
Accounting for saturation of the motor magnetic circuit;
Accounting for elastic mechanical bonds;
Accounting for nonlinear relationships.
AEDs with electric machine FCs have an important advantage: compatibility with the power system, i.e. do not pollute the network.
There are two types of electrical inverters:
Electromachine synchronous IF (EMSPCh);
Electromachine asynchronous FC (EMASCH).
AED with electromachine SFC.
The main element of such a system is a three-phase synchronous generator matched in power with the drive AD. In this case, the output voltage and frequency are determined by the angular velocity of the generator shaft and the magnitude of the excitation magnetic flux. When the speed changes, the output voltage will change. If we take the voltage at the terminals of the phase of the stator winding, it is obvious that when F=const with an increase in the speed of rotation of the shaft, simultaneously with an increase in frequency, the effective value of the output voltage will also increase. In this case, only a proportional control law can be implemented.
fig.6
The PC includes:
The main link is a three-phase synchronous generator (G2);
DPT NV (D2) the output of the G-D system is connected by means of a shaft to the SG;
Auxiliary drive motor AKZ (D1) with unregulated speed.
Quality indicators:
Low efficiency, high cosφ;
P set min = 400%
Advantages of AED with ESCH:
Ease of Management.
Disadvantages of AED with ESCH:
Low efficiency;
The ability to regulate only according to the proportional law.
^
4. Automated asynchronous electric drive using asynchronous electric machine frequency converters.
The main element of such a system is a three-phase asynchronous generator matched in power with the drive AD.
fig.7
Quality indicators:
Two-zone regulation, smooth, stable;
Low efficiency, high cosφ;
P mouth min = 200-400%
Advantages of AED with ESCH:
No negative impact on the network;
Ease of Management.
Disadvantages of AED with ESCH:
Low efficiency;
The presence of a large number of rotating parts;
Unsatisfactory weight and size indicators;
Ability to regulate any law.
The need for autotransformers.
At present, the SFC is the most widely used and promising type of frequency converter as part of an automated electric drive with an AC motor.
HRC is classified according to the following criteria:
According to the structure of energy conversion.
FH with direct conversion.
SFC with DC link.
By type of inverters are divided into:
FC with grid-driven inverters.
FC with autonomous inverter
IF with AIN
FC with AIT
Alternate-switched AI inverter (partial voltage inverter)
AI Inverter with Individual Switching (Voltage Controlled Inverter)
^
5.1 Frequency converter with DC link
Currently, this type of frequency converters is the most widely used type, and, unlike NP+Ch, it is supplied as an independent element of the electric drive.
fig.8
Where U 1 is a three-phase alternating voltage with a constant amplitude.
P 1 - controlled or uncontrolled rectifier, which is designed to convert the input sinusoidal voltage into an output constant (pulsating) voltage.
F - current or voltage filter is designed to smooth out the ripple from the rectifier output.
P 2 is an autonomous current or voltage inverter, designed to convert smoothed direct current or voltage into three-phase alternating.
M - three-phase AC motor with a squirrel-cage rotor.
In the proposed block diagram block P 1 can operate in both controlled and unmanaged modes. At the same time, in the first case, the AI performs the functions of changing only the output frequency of the converter, and the functions of influencing the amplitude of the output voltage are performed by the rectifier. In the second case, AI performs the functions of changing the output frequency and the effective value of the output voltage.
The HC option has an undeniable advantage, which consists in a significant simplification of the control system, despite the presence of the CU. In this case, the entire system is significantly cheaper.
In the case of the LV version, the compatibility of the entire system with the electrical network is significantly improved. However, in this case, the control scheme becomes much more complicated and, accordingly, the entire system becomes much more expensive.
^
6. Autonomous inverters (AI).
According to the degree of controllability, AIs are divided into:
AI with alternate switching.
AI with individual switching.
Let's consider the principle of operation of an alternating-switched MT using the example of a single-phase MT in which the power switches are locked using a switching capacitor.
T 
1, T2 - working thyristors
Let at time t = 0 T2 be open, T1 closed; the input voltage is applied to Rn2, after a period of time equal to the switching period T2, an unlocking pulse is applied to T1. In this case, the input voltage is applied to Rn1, and through the open circuit T1, Rn1, Rn2, a reverse voltage with Sk is applied to T2, as a result of which T2 is locked, etc. The switching period is the duration of the key opening.
According to the shape of the output voltage and current, Ai is divided into: In AIT, the shape of the output voltage depends both on the sequence and duration of switching power switches and on the nature of the load, and the shape of the output current depends only on the sequence and duration of switching power switches.
For AIP, the shape of the output current depends both on the sequence and duration of switching power switches and on the nature of the load, and the shape of the output voltage depends only on the sequence and duration of switching of power switches.
The external difference between AIT and AIP: AIT has an input L - filter, and an input L or LC filter. In addition, if not fully controlled power switches are used in the inverter circuit, then there is one capacitor for each phase of the AIT, and the AIP has one switching capacitor for each power switch.
Consider the operation of a single-phase AIT.
T1, T3 - power switches of the anode group
T2, T4 - power switches of the cathode group
C K - switching capacitor
L is the input filter.
At the first moment of time, two crosswise power switches are in the open state - the first from the anode group, the second from the cathode group. At the moment of unlocking the other two power keys, the first two are locked, and so on. In this case, if the keys T3 and T2 are open, the capacitor is charged in the forward direction, with the keys T1 and T4 open, the capacitor is recharged in the opposite direction.
fig.11
At time t = 0, an unlocking pulse is applied to T1 and T4. the capacitor Ck at this moment is pre-charged, and when T1 and T4 are opened, it is discharged to T3 and T2 in the direction of negative polarity, thereby closing T3 and T2. in the next period of time equal to the switching period T1 and T4, the current through the load resistance will flow in a positive direction. After a period of time, the capacitor is recharged in the opposite direction. At this moment, an unlocking pulse is applied to T3 and T2, the capacitor is discharged in the direction of negative polarity, it locks T1 and T4, the current flows through T4, Zn, and open T2 and will have a negative direction.
^
7. AEPT with a state of emergency having a controlled rectifier in its structure.
At present, there is a tendency to expand the scope of application of controlled rectifiers in the FC structure, in particular, in those electric drives that, due to technological conditions, need frequent braking (ie, for an electric drive operating in the S5 intermittent mode). This is due to the fact that SW has such an important property as bilateral conductivity. This makes it possible to use such an energy-efficient type of braking as regenerative. But the negative properties of hydrocarbons cannot be completely eliminated. Currently, converters are used that contain two input blocks: the first is an uncontrolled rectifier involved in the operation of the drive in the motor mode; the second is the SW involved in the operation of the inverter in the braking mode.
Consider the scheme and principle of operation of the inverter with a thyristor SW and a thyristor AIT, in which the switching of power switches is carried out using switching capacitors.
-
fig.12
The input unit of the converter is a SW built according to a six-stroke bridge three-phase rectification circuit. The main function of the SW, in addition to rectification, is the regulation of the effective value of the output voltage of the converter. To smooth out the rectifier output current ripple, a series L-filter is used.
AIT consists of six power switches, three of which T1, T3, T5 have a common anode and form an anode group; the other three T2, T4, T6 have a common cathode and form a cathode group. The principle of operation of AIT is based on the fact that at the first moment of time there are two crosswise power switches in the open state: one from the anode group, the second from the cathode group. The unlocking of the power keys is carried out at the time of the supply of control pulses from the BUI (multichannel control system). In this case, the sequence of applying pulses to each valve corresponds to their serial number. The locking of the power switches is carried out when any of the three capacitors is discharged in the direction of negative polarity and also corresponds to the order of alternation of the numbers of the power switches.
At output frequency f 2
= 50Hz converter operates in the following mode: the gap between two adjacent control pulses is 
, the opening duration of each key will be 120 0 . In this case, the blocking capacitors C1, C2, C3 must have such a capacity that the time equal to 60 0 hold the charge necessary to lock the next key.
We will demonstrate the operation of the converter using the diagram:
The current from the output of the rectifier has an ideal rectified shape.
Direction of currents in the phases of the mounting cable inverter-motor
from P to D - positive.
from D to P - negative.
fig.13 1. t = 0 Open T1, T6. The circuit current flows through the power switch T1 phase A of the cable and returns to phase C through the open T6. At the same time, C3 is pre-charged, in the time interval 0-60 0 C1 is recharged, and C3 retains its charge.
2. t = 60 0 An unlocking pulse is applied to T2. At the same time, C3 is discharged to T6 and locks it. In the time interval 60 0 - 120 0 T1 and T2 are open. The current flows through phase A to the motor and through phase B from the motor to the inverter. . In this period of time, C2 is recharged, C1 retains its charge.
3. t = 120 0 An unlocking pulse is applied to T3. In this case, C1 is discharged to T1 and locks it. In the time interval 120 0 - 180 0 T2 and T3 are open. The current flows through phase B to the motor, and through phase C from the motor to the inverter. . In this period of time, C3 is recharged, C2 retains its charge.
4. t = 180 0 An unlocking pulse is applied to T4. In this case, C2 is discharged to T2 and locks it. In the time interval 180 0 - 240 0 T3 and T4 are open. The current flows through phase B to the motor, and through phase A from the motor to the inverter. . In this period of time, C1 is recharged, C3 retains its charge.
5. t = 240 0 An unlocking pulse is applied to T5. At the same time, C3 is discharged to T3 and locks it. In the time interval 240 0 - 300 T4 and T5 are open. Current flows through phase C to the motor and through phase A from the motor to the inverter. . In this period of time, C2 recharges C1 guards its charge.
6. t = 300 0 An unlocking pulse is applied to T6. In this case, C1 is discharged to T4 and locks it. In the time interval 300 0 - 360 T5 and T6 are open. Current flows through phase C to the motor, and through phase B from the motor to the inverter. . In this period of time, C3 recharges C2 guards its charge.
To increase the output frequency, it is necessary to reduce the interval between control pulses; for this, we increase the control angle β. Accordingly, with the control law, the effective value of the output voltage will change, in particular, with a proportional control law, with an increase in frequency, the rectifier control angle α will decrease in proportion to the increase in angle β.
A significant drawback of the considered circuit is the need to use high-capacity capacitors necessary to maintain charges in the interval between two switchings. Partially get rid of this shortcoming allows the use of AI with cutting diodes.
fig.14
Here, cut-off diodes D1, D3, D5 and D2, D4, D6 are connected in series in the cathode and anode circuits of the power switches. Their number is equal to the number of keys. These diodes prevent the capacitors from discharging during the switching period of the key and, due to this, significantly improve the readings of the inverter.
^
8. Speed control in AED with FC with SW.
In an AED with a frequency converter and having a controlled rectifier in the structure, the speed control ω is carried out in a wide range, while ensuring sufficiently high quality indicators. The regulation of ω is carried out by acting on the AI with the help of the BIM while simultaneously acting on the SW with the help of the BWM in accordance with the regulation law. In this case, two-zone regulation is possible. However, for mechanisms with M C =
const, and for mechanisms with linearly increasing M FROM upward regulation is limited to what is necessary for this at the same time as increasing the frequency relative to f NOM, increase the voltage. As a result, insulation breakdown may occur. The upward adjustment of ω is used much less frequently than in the downward range and in small aisles.
In the general case, the family of control characteristics will look like:
fig.15
Regulatory quality indicators:
Stability with frequency regulation is high. characteristics in the working part have the same rigidity.
Smoothness is practically unlimited.
High efficiency, however, with deep regulation down from the fundamental frequency, which requires a significant reduction in the control angle α of the rectifier and, in this case, the power factor of the drive as a whole can be very low.
The regulation is mainly carried out with M C = const on the motor shaft.
The direction is two-zone, downward regulation is mainly applied.
Control range D=100÷1.
^
9. Starting in AED with FC with UV.
The start starts at a reduced voltage and at a minimum frequency, which accordingly ensures no inrush current or current minimization and at the same time high starting torques. In this case, the inverter operates with long switching periods of power switches, and the SW with the control angle α = P/2. The energy efficiency of the start in such a system is reduced due to the fact that at the beginning of the start the drive consumes a large amount of the reactive component.
fig.16
Lectures on the discipline "Automated electric drive" Literature 1. Chilikin M.G., Sandler A.S. General Electric Drive Course (EP).-6th ed. -M.: Energoizdat, - 576 p. 2. Moskalenko V.V. Electric drive - M .: Mastery; Higher School, -368 p. 3. Moskalenko V.V. Electric drive: Textbook for electrical engineering. specialist. -M.: Higher. school, - 430 p. 4. Handbook of automated electric drive / Ed. V.A. Eliseeva, A.V. Shiyansky.-M.: Energoatomizdat, 1983. – 616 p. 5. Moskalenko V.V. Automated electric drive: Textbook for universities.- M.: Energoatomizdat, p. 6. Klyuchev V.I. Theory of electric drive. - M.: Energoatomizdat, p. 7. GOST R-92. Electric drives. Terms and Definitions. Gosstandart of Russia. 8. Handbook of an electrical engineer with.-x. production / Tutorial.-M.: Informagrotech, p. 9. Guidelines for the implementation of laboratory work on the basics of the electric drive for students of the electrification faculty of agriculture. / Stavropol, SSAU, "AGRUS", - 45 p. 10. Savchenko P.I. Workshop on electric drive in agriculture. – M.: Kolos, p. Recommended sites on the Internet: Lectures on the discipline "Automated electric drive" Literature 1. Chilikin M.G., Sandler A.S. General Electric Drive Course (EP).-6th ed. -M.: Energoizdat, - 576 p. 2. Moskalenko V.V. Electric drive - M .: Mastery; Higher School, -368 p. 3. Moskalenko V.V. Electric drive: Textbook for electrical engineering. specialist. -M.: Higher. school, - 430 p. 4. Handbook of automated electric drive / Ed. V.A. Eliseeva, A.V. Shiyansky.-M.: Energoatomizdat, 1983. – 616 p. 5. Moskalenko V.V. Automated electric drive: Textbook for universities.- M.: Energoatomizdat, p. 6. Klyuchev V.I. Theory of electric drive. - M.: Energoatomizdat, p. 7. GOST R-92. Electric drives. Terms and Definitions. Gosstandart of Russia. 8. Handbook of an electrical engineer with.-x. production / Tutorial.-M.: Informagrotech, p. 9. Guidelines for the implementation of laboratory work on the basics of the electric drive for students of the electrification faculty of agriculture. / Stavropol, SSAU, "AGRUS", - 45 p. 10. Savchenko P.I. Workshop on electric drive in agriculture. – M.: Kolos, p. Recommended sites on the Internet:
Source of electrical energy (IEE) Control device (CU) Converter device (PRB) Electric motor device (EM) M Transmission device (TRD) Consumer of mechanical energy (PME) U,I,f d F d, V d M m (F m), ω m (V m) tasks Figure 3 - Structural diagram of the AED
3 Efficiency of AED As for any electromechanical device, an important indicator is the efficiency of AED = PRB · ED · PRD at rated load is 60-95%.
4 Advantages of AED 1) low noise level during operation; 2) absence of environmental pollution; 3) a wide range of powers and angular speeds of rotation; 4) the availability of regulation of the angular velocity of rotation and, accordingly, the performance of the process unit; 5) the relative ease of automation, installation, operation in comparison with heat engines, for example, internal combustion.
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