RU1777227C - Frequency-controlled induction-motor drive - Google Patents

Abstract

Usage: various mechanisms, pumps, fans, compressors, load test stands of diesel engines. SUMMARY OF THE INVENTION: the inputs of the flow amplitude setting unit 23 are connected to the output of the analog output signal generator 15 and to the output of the phase voltage sensor 6, said block 23 being configured with a functional frequency adjuster 24, dividing units 25 and 26, and a voltage limiter 27 with a control input input, adder 28 and non-linear voltage amplitude regulator 29. In this case, the control characteristics of the drive are improved in terms of the speed control range and torque limit. 6 ill.

Description

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The invention relates to electrical engineering, in particular to asynchronous variable frequency drives with a frequency converter based on autonomous current inverters.

The main application describes a frequency-controlled asynchronous electric drive containing an asynchronous squirrel-cage motor connected via phase current and voltage sensors to a frequency converter with an autonomous current inverter having two control inputs: in amplitude and frequency of an alternating current output, and to the first the input is connected to the output of the unit for setting the amplitude of the current, the input of which is connected to the device for setting the motor torque (in particular, it can be a speed controller), and to the second input of the converter A key frequency controller with five inputs is connected, the first input is connected to the block of the analog signal for setting the output frequency (in particular, the tachogenerator or the adder of the tachogenerator and torque generator signals, or the engine speed controller), the second and third inputs are connected to the outputs of the logical unit comparing the logical signals of the actual current of the motor and the logic signals of the phase currents, connected by the inputs to the current and voltage sensors, and the fourth and fifth inputs of the key frequency controller are connected are directed to the outputs of the generator of logic signals for controlling the amplitude of the stream, the inputs of which are connected to the output of the device for setting the moment and the output of the relay controller for the amplitude of the stream, measured by the signals of the motor flux linkages.

The disadvantage of the prototype is the limitation on the upper value of the engine speed and. as a consequence, the inability to implement drives for a number of applications.

The purpose of the invention is to expand the scope of this device by improving the control characteristics of the drive in the range of speed control and torque limit.

This goal is achieved by the fact that in the frequency-controlled asynchronous electric drive, the unit for setting the amplitude of the flow is made with two additional inputs and is equipped with a functional frequency regulator, two division units, a voltage limiter with a control input, an adder and a non-linear regulator of the amplitude of the actual voltage and a voltage setting unit proportional to the voltage of the supply network, when

the output of the functional frequency controller is connected to the interconnected inputs of the dividers of the first and second division devices, the input of the second divisible

the division unit is designed to supply a constant voltage, the output of the first division unit is connected to the input of the voltage limiter, the control input of which is connected to the output of the second unit

0 divisions, the output of the voltage limiter is connected to the first input of the adder, the second input of which is connected to the output of the nonlinear voltage amplitude regulator, and the output of the adder forms

5, the output of the stream amplitude setting unit, the main input of which is formed by the input of the divisible first division device, the first additional input of the stream amplitude setting unit, formed by the input of the function of the opal frequency adjuster, is connected to the output of the analog output signal shaper, and the second additional input of the stream amplitude setting unit formed by the input of the unit for measuring the amplitude of the actual voltage, is connected to the output of the phase voltage sensor.

A distinctive feature of the invention is the presence of new block connections.

0 setting the amplitude of the flow with the output of the driver of the analog signal of the output frequency and with the output of the phase voltage sensor, as well as the execution of the unit itself according to the above principle, which allows 5 improve the control characteristics of the drive in the range of speed control and limiting moments, while achieving expansion fields of application.

0 Fig. 1 is a functional diagram of an asynchronous electric drive control device; in FIG. 2 is a functional diagram of a flow amplitude setting unit; Fig. 3 is a functional diagram of a key 5 frequency controller; in FIG. 4 is a functional diagram of a logic generator for controlling amplitude of a stream; in FIG. 5 - characteristic of the functional converter; in FIG. 6 is a functional diagram of a non-linear voltage regulator.

An asynchronous electric drive control device (see, Fig. 1) consists of a frequency converter 2 based on a self-contained current inverter with two inputs 3 and 4 in amplitude and frequency, respectively, connected by output terminals through phase current sensors 5 and voltage 6 to an induction motor 1 serially connected moment setting devices

motor 7 and a current amplitude setting unit 8, the output of which is connected to the first 3 input of the frequency converter 2, and a key frequency controller 9 with five inputs 10-14 is connected to the second input 4.

The first input 10 is connected to the analog frequency reference unit 15. The second and third inputs 11 and 12 are connected to the logical comparison unit 16, the inputs of which are connected to the unit for generating logical signals of the currents of the motor 18 by the signals of the phase currents from the sensor 5 and the unit for generating the logical signals of the phase setting currents 17, the inputs of the latter are connected to the output of the torque reference device 7 and the outputs of the phase flow coupler 19, connected by the inputs to the current sensors 5 and voltage 6. The fourth 13 and fifth fifth inputs of the key regulation 9 are connected to the outputs of the generator of logic signals for controlling the amplitude of the stream 20, the first input of which is connected to the output of the device for setting the moment 7, and the second to the output of the relay controller of the stream 21, at the input of which the amplitude signal of the actual stream from the output of the block 22 connected by the inputs is compared with the outputs of the phase flow coupler 19. and a signal for setting the amplitude of the stream from the output of block 23.

The unit for setting the amplitude of the stream 23 (see Fig. 2) contains a functional frequency reference 24, the first 25 and second 26 division blocks, a voltage limiter 27 with a control input, an adder 28 and a nonlinear voltage amplitude regulator 29, the inputs of which are connected to a unit for measuring the amplitude of the actual voltage 31 and a unit for setting a voltage 30 proportional to the voltage of the supply network. The output of block 24 is connected to the combined inputs of the dividers of the dividers 25 and 26, and a constant voltage is applied to the input of the dividend block 26. The output of block 25 is connected to the input of the limiter 27, the control input of which is connected to the output of the block 26. The output of the limiter 27 is connected to the first input of the adder 28, the second input of which is connected to the output of the nonlinear controller 29, and the output of the adder 28 forms the output of the block 23. When this, the main input of block 23 is formed by the input of the divisible block 25, the first additional input of block 23 is formed by the input of the functional setter 24 and connected to the output of the former 15, and the second additional input of block 23 is formed by the input of the block 31 and connected to the output of dates ika phase voltages 6.

The torque reference device 7 may be a PI speed controller in the case; if the drive solves the problem of controlling the rotational speed of the mechanism, or 5 I-torque controller, if the drive solves the problem of creating a load moment for the mechanism.

The analog frequency reference unit 15 may be a frequency sensor

0 rotation (see prototype) or an external frequency reference device (see A.S. USSR No. 1334347, class N 02 7/42).

The key frequency controller 9 (see Fig. 3) contains an operational amplifier

5 32. the input of which is supplied with a frequency reference signal at input 10 formed by the common point of the connected resistors 33, 35, 38 and 40, the second point being connected to the input of the amplifier 32, 33 directly, and the input 35 through the controlled key 34, input 38 through a controlled key 39, input 40 through a controlled key 41. On the feedback circuit, the amplifier 32 is surrounded by a resistor 36, shunted by a controlled key 37. The inputs of the controlled keys form the inputs of block 9: 34-11.37 -12. 39-13, 41-14. The output of the amplifier 32 forms the output of block 9.

Logic Shaper

The amplitude control 0 of the stream 20 (see Fig. 4) contains a null-organ 42, the input of which forms the input of the driver 20, which is connected to the output of the reference of the moment 7, and the output is connected to the first input of the negating OR logic element 43. and the second input of the element 43 forms the second input of the driver 20, connected to the output of the relay controller of the flow 21. The output of the element 43 through the logic element

0 And 47 forms the first output 13 of block 20, and through series-connected elements NAND 45 and 46 forms the second output 14 of block 20, and the second inputs of the elements 46 and 47 are connected to the relay element 5 volume 44.

An asynchronous electric drive control device operates as follows.

Frequency converter 2 generates

0 alternating current with the amplitude specified by the output signal of the unit for setting the amplitude of the current 8, and the frequency specified by the output signal of the key frequency controller 9. Motor 1. powered from the 5 liter frequency converter 20 develops the moment specified by the device 7. The torque of the induction motor is determined by the amplitude of the stator current vector and its orientation relative to the rotor flux linkage vector. In particular, in the implementation of economic

of the asynchronous motor control law (Acad. M.P. Zhostenko), the shift angle between the current vector It and the flux linkage t / Ј remains unchanged and changes abruptly when the sign of the moment changes.

The motor rotor flux linkage is determined in block 19 from the signals of the current sensors 5 and the voltage of the motor. The phase flow signals together with the motor torque reference signal to the block 17 generate logic signals for setting the stator current, i.e. determine the period of time during which the motor currents of certain phases of a certain polarity must exist. These signals define the angle of shift between the vectors Ti and 1 / Ј. The mismatch of the logical signals of the actual motor current, determined in block 18 by the signals of the current sensors 5, in comparison with the set ones from the outputs of the block 17 indicates a phase error of the real vector h relative to the set one. This error appears in the logical comparison block 16, and in the function of this error in the block of the key frequency controller 9, the analog signal for setting the frequency of the inverter from the output of block 15 is corrected.

If the logic signal of the real current lags behind the logic signal of the current setting, then the key 34 closes and the output signal of the amplifier 32 is increased compared to the input signal at point 10. If the logic signal of the real current is ahead of the logic signal of the current setting, then the time the mismatch of the logic signals closes the key 37 and the output signal of the amplifier 32 becomes equal to zero. As a result of the operation of the key corrector 9, the average voltage value at the output of the operational amplifier 32 differs from the input signal at point 10. This average voltage determines the frequency of the inverter.

As a result of a change in the frequency of the inverter and, consequently, the frequency of the stator current, the vector TI is set to a predetermined position, thereby reproducing a predetermined motor torque. Errors of sensors 5 and b, errors in the operation of blocks 17, 18, 16, and 19 lead, as a rule, to the fact that the specified shift angle between the vectors h and $ must be corrected, but the direct measurement of the motor moment is difficult. Therefore, the correction is performed as a function of the error signal of the amplitude of the stream 1 / 2- which is also due to two parameters; the amplitude of the stator current 11 and the angle of shift between the vectors in. The signal of the amplitude of the stream $ 2 is determined in block 22 by the signals of the phase flows from the outputs of block 19 and is compared with the specification of the amplitude of the stream, which is generated as a function of the amplitude of the current in block 23. The relay controller 21 determines the error sign. If the actual amplitude of the flow is less than the specified value, it is necessary

reduce the absolute value of the angle between the vectors h and ifa, which in the motor mode is provided by a decrease in the frequency of the inverter, and in the generator mode by an increase in the frequency. In the first case

keys 39 and 41 must be disconnected, and in the second case, closed.

When the keys 39 and 41 are switched, a deliberate change in the inverter output frequency occurs, which is restored automatically due to a mismatch between the logic signals of the reference and the actual motor current, in other words, due to the deviation

actual value of the angle 0 from the specified value. Thus, when the amplitude of the flux Φ 2 decreases with respect to the value set by the block 23 in the motor mode, the keys 39 and 41 are turned off, the inverter output frequency decreases, an error signal also appears at the output of the block 16, which closes the key 34, restoring the frequency. The introduction of a constant error between the logical signals of the currents in this case means

a decrease in the absolute value of the angle O, which at a given amplitude of the current leads to an increase in the amplitude of the flow. The corresponding management of keys 39 and 41 is carried out in block 20, where

relay flow control signals and a torque signal (to highlight its sign). Flow control is disabled when a zero signal occurs at the output of block 44 (in commissioning mode), resulting

whereby one of the keys 39 and 41 closes, the other opens. In strict wording, the law of M.P. Kostenko has a limited scope due to the fact that

1. It does not take into account the magnetic nonlinearity of the engine. At big moments

the angle between the vectors ft and y2 must vary.

2.When regulating the engine speed by attenuating the flow (in this case, increasing the output frequency of the converter at a fixed voltage is meant), the ratio between the amplitudes I and 2 changes, in other words, the angle 0 must change.

3.When the electric drive operates as a loading device, when the asynchronous motor operates in the generator mode, the autonomous inverter operates in the compensated rectifier mode, and the rectifier in the network-driven inverter mode, there is a danger of the emergency mode of the inverter overturning, which is prevented only by amplitude control voltage of the motor through the regulation of the amplitude of the flow,

4. A feature of autonomous current inverters when operating on an induction motor is a fundamental limitation of the upper value of the inverter output frequency from the conditions of completeness of switching processes in the inverter, the substantial duration of which is due to the relatively large capacity of the switching capacitors. An increase in the upper value of the operating frequency is possible with a corresponding increase in the angle 0. The necessary law of controlling the angle of the current, frequency, and voltage functions of the motor is implemented by arranging in the block 23 a signal for setting the amplitude of the flow, which is processed by the closed-loop control system for the magnitude of the flow by acting on the angle 9. Let us consider the functioning of block 23 (see Fig. 2), taking into account the above-mentioned drive operating modes, which require special control of the angle and flow of the engine.

The setting of the amplitude of the flow varies with the current. In mode 9 const, these values are proportional, in other words, the signal at the input of block 23 from the current setting device 7 passes to the output of block 23.

However, at high currents, the signal at the output of block 23 is limited by a limiter 27. This means that the motor current grows at a constant amplitude of the flow, which is ensured by an increase in the absolute value of angle 9. The proportionality coefficient between the current and the flow depends on the frequency of the inverter. One of the simplest and most effective solutions for functional 24 is shown in FIG. 5. At frequencies less than fi, the coefficient of proportionality between current and current is equal to Fi (f)

(the output signal of block 25 is equal to F /, L is constant and maximum. At frequencies higher than fi, the proportionality coefficient decreases, which corresponds to the field attenuation mode, while the problem of increasing the angle of elevated

frequencies to ensure switching performance of the inverter. In addition, with increasing frequency, the limit value of the flow is limited - the limiter signal

inversely proportional to the output of functional 24.

Additionally, setting the amplitude of the flow from the output of the adder 28 is limited by the output of the voltage regulator 29 to prevent the inverter from tipping over when the motor is operating in electromagnetic brake mode at higher frequencies.

If the output voltage

the inverter (the output signal of block 31) exceeds the limit value proportional to the voltage of the network (the output signal of block 30), the non-linear controller 29 enters into operation (see Fig. 6) and reduces the voltage amplitude of the motor by decreasing the flow amplitude by increasing the modulus .

Claims (1)

The claims Frequency-regulated asynchronous electric drive according to ed. St. No. 1282302, characterized in that, in order to improve the control characteristics of the drive in the range of speed control and limit moments, the unit for setting the amplitude of the flow is made with two additional inputs and is equipped with a functional frequency adjuster, two divisions, a limiter voltage with a control input, adder and non-linear voltage amplitude regulator, the inputs of which are connected to the unit for measuring the amplitude of the actual voltage and the voltage setting unit; proportional to the voltage of the supply network, while the output of the functional frequency adjuster is connected to the interconnected inputs of the dividers of the first and second division blocks, the input of the dividend the second division unit is designed to supply a constant voltage, the output of the first division unit is connected to the input of the voltage limiter, the control input of which is connected to the output of the second unit, the output of the voltage limiter is connected to the first input of the adder, the second input of which is connected to the output of the nonlinear voltage amplitude regulator, and the output of the adder forms the output of the unit for setting the amplitude of the flow, the main input of which is formed by the input of the divisible first division unit, the first additional the input of the flow amplitude setting unit formed by the input of the functional frequency adjuster is connected to the output of the analog signal driver is formed by the input of the measuring unit of the amplitude output frequency, and the second additional plate of the actual voltage, the connected input of the unit of setting the amplitude of the flow, than to the output of the phase voltage sensor. 9b. 3 figure 1 FY2. 4 29 I ABOUT