SU1453574A1 - Frequency-controlled electric drive - Google Patents

Abstract

The invention relates to electrical engineering. The aim of the invention is to improve the energy performance by reducing the reactive power consumed from the network. The variable frequency drive contains a magnetizing current detecting unit 18, inputs connected to the outputs of sensors 2 and 3 of the voltages and currents of the phases of the stator winding of the induction motor 1, through which the engine is connected to the frequency converter 4. The output of unit 18 is connected to the input of the flow converter 19, another the input of which is connected to the output of the re

Description

one

The invention relates to electrical engineering, and specifically to frequency-controlled electric drives based on asynchronous motors with a short-circuited rotor and can be used in systems for which the increased energy indices to the simplicity of the design are decisive.

The purpose of the invention is to improve the energy performance by reducing the reactive power consumed from the network.

FIG. 1 shows a functional diagram of the frequency-controlled drive; FIG. 2 is a functional diagram of a stator current task driver; in fig. 3 is a functional diagram of a functional magnetization-to-current converter; in FIG. 4 is a vector diagram of an asynchronous motor.

The frequency-controlled electric drive contains an asynchronous motor 1 (Fig. 1) connected via a sensor of 2 phase voltages and a sensor of 3 phase currents to the outputs of the power frequency converter 4, a tachogenerator 5 mounted on the shaft of the asynchronous motor 1, block 6 of the comparison, connected an output to the input of the rotational speed controller 7, a driver of 8 stator current tasks with two inputs of the component currents and

frequency input, a two-phase three-phase signal converter 9, connected by inputs to the corresponding outputs of the shaper of 8 tasks of the stator current, - and the outputs through

shaper 10 control actions - to the control inputs of the power converter 4 frequency, the EMF calculation unit 11, connected by outputs to the corresponding inputs of the converter 12 two-phase signal to a three-phase, large-scale amplifier 13, connected to one of the inputs of the adder 14, and block 15 multiply. In this case, the first input of block 6

Comparison is designed to supply a control signal, the second input is combined with another input of the adder 14 and connected to the output of the tachogenerator 5. The output of the rotational frequency controller 7 is connected to the input of the scale amplifier 13 and to the corresponding input of the current component of the stator current command 8. The output of the converter 12 is two-phase

signal to the three-phase and the output of the sensor 3 phase currents are connected to

In accordance with the corresponding inputs, there are 10 control actions.

A comparison unit 16, a flow regulator 17, a magnetization current detection unit 18, a functional magnetizing current converter 19 to a flow and a voltage converter 2 are connected to the variable-frequency drive and the voltage converter 2 is connected to the output of the adder 14, and the output to the frequency input Former 8 tasks of the stator current. The first input of the comparison unit 16 is combined with the first input of the comparison unit 6, the second input of the comparison unit 16 is connected to the output of the functional converter 19, and the output through the flow controller I7 is connected to the corresponding input of the current component of the stator current command 8. The inputs of the multiplication unit 15 are connected to the outputs of the adder 14 and the flow controller 17, and the output is connected to one of the inputs of the EMF calculation unit 11, the other input of which is connected to the output, the voltage of the converter 20 is frequency. The inputs of the magnetizing current detecting unit 18 are connected to the outputs of sensors 2 and 3 of the phase voltages and currents, and the output to one of the inputs of the functional converter 19, the other input of which is connected to the output of the rotational speed controller 7.

The shaper 8 of the stator current tasks is equipped with two generators 21 and 22 (Fig. 2) of the Walsh functions for the formation of sinusoidal and cosine functions, eight blocks 23-30 of analog switches. The two inverters 31 and 32, the four weighting factors, the four blocks 33-36, the subtractor 37 and the adder 38.

The interconnected inputs of generators 21 and 22 and the inputs of inverters 31 and 32, respectively, form the frequency input and the inputs of the current generator components 8 stator current tasks.

The outputs of the generator 21 Walsh functions are connected to the control inputs of blocks 23-26 of the analog switches, and the outputs of the generator 22 functions of the Walsh

connected to the control inputs of blocks 27-30 of analog switches. The outputs of the blocks 23 and 24 of the analog switches are connected to the inputs of the block 33 of the task of weighting factors, the output of which

0

five

0

It is connected to the first input of subtractors 37. The outputs of blocks 25 and 26 of analog switches are connected to the inputs of block 34 for setting weights, the output of which is connected to the first input of adder 38. The outputs of generator 22 are connected to control inputs of blocks 27-30; analog keys. The outputs of the blocks 27 and 28 of the analog switches are connected to the inputs of the weighting factors block 35, the output of which is connected to the second input of the adder 38.

The outputs of the blocks 29 and 30 of the analog switches are connected to the inputs of the weighting factors block 36, the output of which is connected to the second input of the subtractor. The non-controlling inputs of the blocks 24 and 28 are connected to the input of the inverter 31 connected by an output to the non-controlling inputs of the blocks 23 and 27 of the analog switches. The non-controlling inputs of the blocks 26 and 30 of the analog switches are connected to the input of the inverter 32, which is connected by output to the non-controlling inputs of the blocks 25 and 29 of the analog switches. The outputs of the subtractor 37 and the adder 38 form the outputs of the imaging unit 8 tasks of the stator current.

The function of the magnetization-to-flow current converter 19 can be performed with analog switches 39-42 (FIG. 3), a comparators block 43 and an adder implemented on the operational amplifier 44. The combined inputs of the keys 39-42 form one of the inputs of the converter 19, the other input which is formed by the input of the comparators block 43, the outputs of which are connected to the control inputs of the keys 39-42 connected by the outputs to the input of the sum of -or 44.

It follows from the vector diagram (Fig. 4) that if the magnetization current is maintained at a constant level, then as the load increases, the linkage of the rotor decreases by

0

five

0

five

50

  With cosq).

(one)

where tp is the angle between vector 1 and current

magnetization and rotor flux coupling.

55 Having made a piecewise linear approximation, taking into account the magnetization curve, one can go from coupling to current:

ui ,,, K (I,) lJl-costf), (2)

1453574

de pr pr v i n e

where K (1) is the proportionality coefficient between the current and the flux linkage, depending on the shape of the magnetization curve and the magnitude of the magnetizing current Ij. In order for the rotor flux linkage to remain unchanged as the load increases and the induction motor to operate with reduced losses, it is necessary to adjust the component of the magnetizing current in accordance with the expression

 “Id.T.

K (1c) 1c + & i, ii “K (1c) 1c) 2– ω8 (p), de K (1„) 1,

(3)

M

nd

the term ensuring the flux linkage of the air gap at a constant level regardless of the engine operating mode; The term that provides an increase in the flow coupling of the air gap by an amount that ensures the constant flow coupling of the rotor when the engine load changes.

Learn the ratio of Xas S.

tgif

R,

(four)

where X is the transient inductive impedance of the rotor; Rj is the active resistance of the rotor

S - slip,

determine the value 1 and substitute it in the expression (3)

K (I ..) IJ2-cosaTctg

Xjs- S

-) (five)

d.T

From the expression (5) it follows that at 8 0, i, ij.T. K (IM) I ". and with increasing slip, the value of.-r should increase to a non-linear relationship, which the functional converter 19 approximates. When S O, the output of the comparators block 43 yields a signal, the keys 39–42 trigger and the transfer coefficient of the operational amplifier 44 has a maximum value. As the load increases, the slip increases, a part of the comparators of the block 43 is activated, a part of the keys 39-42 breaks its chains 1 signal at the output

0

five

0

25

The de-amplification amplifier 44 drops off with a constant supply signal, which leads to an increase in the error signal at the input of the flow regulator 17. Moreover, the change in the transmission coefficient of the operational amplifier 44 is carried out in such a way that the reference to the magnetizing current changes as the slip changes in accordance with the extrusion (5). .

Walsh functions, "used in the synthesis of driver 8, allow approximating harmonic oscillations and performing harmonic functions multiplication by arbitrary functions, which allows relatively simple means of" bind "the Park transform, i.e. for the component currents i, j, and i, move from a rotating coordinate system to a fixed coordinate system. In the magnetizing current calculating unit, by the measured phase currents and voltages and the known parameters of the motor, the XotC or

KOI

n

where is the circular frequency

thirty

35

the motor winding supply, Ij, is the magnetizing current. Since the functional converter 19 is a non-linear element, a current can be supplied to its input as a signal Ki1c, or a signal K. If you send a signal Ki1, this signal determines the magnetic flux of the air gap of the asynchronous motor. Moreover, the magnetic flux of the air gap will be maintained at a given level both when the frequency changes and when the load changes. And since the magnetic flux is determined through the reactive power and the inductive constants of the machine, the magnitude of the magnetization current will not be sensitive to the action of destabilizing factors (the change in active resistance depending on the thermal mode of the engine).

40

In addition, a change in the transfer coefficient of the functional converter 19 in the slip function allows one to obtain at the output of this converter a signal proportional to the rotor flux linkage.

Variable frequency drive works as follows.

The inputs of blocks 6 and 16 of the comparison receive the signal of the assignment U.j, and

the second input of the comparison unit 6 and the adder 14 receives a signal from the output of the tachogenerator 5. The output of the block

6th, an error signal appears at the input to the controller

7 rotational frequency, at the output of which a signal appears that determines the torque component of the engine. At the same time, the reference signal arrives at the first input of the block.

16, to the second input of which a signal from the code of the functional converter 19 of the magnetizing current to the rotor flux linkage is applied. At the output of the comparator unit 16, an error signal appears between the setpoint value of the rotor flow and the actual value, which is fed to the input of the flow controller 17, the output of which determines the flow component of the motor. Thus, the signals i 1 are sent to the input unit of the driver 8. "Li ii2. (J In addition, the signal from the output of the speed regulator 7 through the scale amplifier 13, in which the output signal of the block 7 is multiplied by, is fed to the second input of the adder 14. At the output of the adder proportioned flax rotational frequency reference rotor flux linkage vector which, via inverter 20 the voltage - frequency is input to frequency driver 8 stator current tasks, wherein component Yu-

current i

nd

and 1

tt (v

determined by the rotating coordinate system, is converted into components of the current i Q. and i, Q-for a fixed coordinate system according to the well-known Park transform.

Shaper 8 is implemented using Walsh functions. The frequency signal is fed to the inputs of the 2 1 and 22 Walsh function generators (Fig. 2). In the generator 21, the Walsh functions are formed to approximate sinusoidal oscillations, and in the generator 22, the Walsh functions form a cosine-sinusoidal oscillations. In blocks 23-30 of the analog keys and in blocks 33-36 of the setting of weighting factors, harmonic functions are multiplied by the corresponding currents. In the subtractor 37 and the adder 38, the resulting products are added according to the transformation

0

five

0

five

0

five

0

five

0

five

The park, and at the output, the signals and i, Qj appear, defining the setting of the stator current in the fixed coordinate system. In the converter 9, a transition from a two-phase coordinate system to a three-phase one is carried out, which ensures that the driver 1 o controls the effects of the tasks on the current of each phase on the driver. In order to compensate for the effect of the EMF, the shaper of the control actions is given by the reference signals of the phase EMFs, e, e from the outputs of the converter 12. The phase electromotive forces are determined by blocks 11, 12 and 15. In the multiplication unit 15, the reference to the rotation frequency of the stator current oioi is multiplied on the current task flow i, 2d ie we have:

e JK (I), - i ,, 2j.

In block 11 of the calculation of the emf, the output of the multiplier block 15 and the frequency signal oioj are the emf in a fixed coordinate system. Moreover, this block is made according to the same functional scheme as the task generator 8, but is simpler than the latter, since in block 11 the harmonic functions are multiplied by one input signal (output of block 15). Thus, block 11 can be performed as part of block 8, if only the channel input is used, to which the output signal of block 15 is applied, and the output of block 11 is to take the output of block 33 for specifying weights (Fig. 2) and output of block 35 setting weights 35. The output signal of block 11 determines the EMF values in a two-phase stationary coordinate system, which is converted by block 12 into signals acting in a three-phase coordinate system, unit e, e. These signals are fed to a 1 O driver and comp siruyut negative effect of EMF motor.

Information from the sensors of 3 phase currents and sensors of 2 phase voltages is fed to the inputs of the magnetizing current detecting unit 18, in which, taking into account the known parameters of the motor, the KoTC signal determining the magnetic flux in the air gap is determined. If the motor slip is close to zero, then at the output of the functional converter 19 there is a signal proportional to the magnetic flux of the AIR gap. This signal in comparison unit 16 is compared with the reference signal, and an error is fed to the flow controller 17. As the load increases, the signal at the output of the speed controller 7 increases, some of the comparators 43 (FIG. 3) operate, the corresponding switches 39-42 are broken and the signal at the output of the functional converter 19 decreases, which leads to an increase in the error at the output of the flow regulator 17 . The component of the current increases, which increases the magnetic flux of the engine.

The change in the transmission coefficient of the functional converter 19 in the slip function varies almost without redundancy. Thus, as the moment increases, the task is increased by two components

and 1,

which improves dynamics

lid t2 (j, chesky drive performance. At the same

time, with a decrease in the moment of resistance, the component of the current does not remain unchanged (decreases with decreasing load), which increases the energy performance of the control system.

Thus, more accurate maintenance of the component of the motor current determining the magnetic flux and regulation of this component as a function of the load provides for reduction of the reactive power consumed from the network and increasing the energy performance of the electric drive in comparison with the known electric drive. In addition, the dynamic performance of the drive is improved by increasing the dynamic torque of the engine, which increases as the development of the dynamic drop in the rotational speed occurs as the two increase the current: i (2, j and i n)

Claims (2)

1. A frequency-controlled electric drive containing an asynchronous motor connected via a phase voltage sensor and a phase current sensor to the outputs of a power frequency converter, a tachogenerator mounted on an asynchronous motor shaft, the first comparison unit connected by an output to the regulator 0 input five 0 five 0 5 do 45 rotational speed torus, current positioner with two inputs of component currents and frequency input, the first two-phase three-phase signal converter connected by inputs to the corresponding outputs of the positioner current task generator and outputs through the driver of control actions to the control inputs of the power frequency converter , the EMF calculation unit connected by the outputs to the corresponding inputs of the second two-phase signal converter into a three-phase, large-scale amplifier connected by the output to one of the inputs of the adder, and a multiplier, the first input of the first comparison unit is designed to supply a control signal, the second input is combined with another input of the adder and connected to the output of the tachogenerator, and the output of the speed regulator is connected to the the input component of the current of the current task generator of the stator, the output of the second two-phase converter of the three-phase signal and the output of the phase current sensor are connected to other relevant inputs of the control driver In order to improve the energy performance by reducing the reactive power consumed from the network, a second comparator unit, a flow controller, a magnetization current detection unit, a functional magnetization current-to-current converter and a voltage converter — a frequency connected by an input are introduced. to the output of the adder, and the output to the frequency input of the stator current task generator, while the first input of the second comparison unit is combined with the first input of the first comparison unit, the second input of the second the comparison unit is connected to the output of the magnetization-to-flow functional current converter, and the output through the flow controller is connected to another input component of the current of the stator current task generator, the inputs of the multiplication unit are connected to the outputs of the adder and flow controller, and the output to one of the inputs of the unit EMF calculation, another input of which is connected to the converter output mains voltage, magnetizing current detection unit inputs are connected to the outputs of phase voltage and current sensors, and the output is connected to one of the inputs of the functional magnetization current converter into the flow, the other input of which is connected to the output of the speed regulator. 2. The actuator according to claim 1, characterized in that the stator current task driver is equipped with two Walsh function generators for generating sinusoidal and cosine-wave oscillations, respectively, eight blocks of analog switches, four blocks of weighting factors, two inverters ; subtractor and adder, while the interconnected inputs of these generators of Walsh functions and inputs of inverters form respectively the frequency input and the inputs of the component current of the stator current task generator, the code of the first Walsh generator for forming a sinusoidal fusestion is connected to the jmpaB-inputs of the first the second, third and fourth blocks of known keys, the codes of the first and second blocks of analog switches are connected to the inputs of the first block of the assignment of weights, the output of which is connected to The first entrance. the subtractor, the outputs of the third and fourth blocks of analog switches are connected to the inputs of the second set of weighting coefficients, the output of which is connected to the first input of the adder, the outputs of the second generator of Walsh functions to form cosine functions, are connected to the control inputs of the fifth, sixth, seventh and eighth the analog key block, the outputs of the fifth and sixth block of the analog keys are connected to the inputs of the third weight setting unit, the output of which is connected to the second input of the adder, the outputs from the seventh and eighth block of analog switches is connected to the inputs of the fourth block of the weight factors, the output of which is connected to the second input of the subtractor, the non-controlling inputs of the second and sixth block of analog switches are connected to the input of the first inverter connected to the output of the non-controlling inputs of the first and fifth analog blocks keys, non-controlling inputs of the fourth and eighth analog switches are connected to the input of the second inverter connected by output to the non-controlling inputs of the third and seventh block of analog switches whose, and the codes of the subtractor and the adder, form the outputs of the task generator of the stator current. W4 JE m Ultrasound  I Fi.Z