SU1372580A1 - Electric drive - Google Patents

Abstract

The invention relates to electrical engineering and can be used in the chemical, mining, metallurgical and other industries of the national economy. The aim of the invention is to improve the energy performance by reducing electrical losses and improving the accuracy of stabilizing the rotation frequency. This goal is achieved by introducing a filter 24 into the electric drive of the limiting amplifier 23. The limiting amplifier 23 is connected between the output of the frequency regulator 19 and the second input of the phase regulator. The filter 24 is connected to the output of the unit 22 of the stator current module, and the output is connected to the input of the proportional-differentiating link 13. The second input of the dividing block 14 is connected to the output of the EMF sensor 17 of the engine 1. In the electric drive, the flow is adhered to as a function of time, which provides savings electricity and automatic stabilization at a given level of rotational speed when the load on the motor shaft 1 changes. 1 Cp f-ly, 6 ill. (C (L to ate ICX) ful /

Description

The invention relates to electrical engineering and can be used in various sectors of the industry: chemical, mining, metallurgical, nuclear power and others to regulate the speed of a powerful asynchronous electric motor drives fans, compressors, gas blowers and others, where energy saving and lowering are decisive. electrical losses.

The aim of the invention is to improve the energy performance by reducing electrical losses and improving the accuracy of stabilizing the rotation frequency.

Figures 1 and 2 show the functional diagrams of electric drives with three-phase and phase-to-phase asynchronous motors, respectively; Fig. 3 is a schematic block diagram of the task of the stator current module of Fig. 4 is a schematic diagram of the amplifier-limiter; in Fig. 5, the adjustment curves of the electric drive; 6 is a vector diagram of an asynchronous motor.

The electric drive contains an asynchronous motor 1 (Fig. 1) connected by a three-phase winding to the output of the converter section 2, consisting of a series-connected controlled rectifier 3, a smoothing droplet 4 and an autonomous inverter 5, the control systems of the rectifier 6 and the inverter 7 of the regulator 8 the current connected by the output to the input of the system 6 of the control of the rectifier, and one of its inputs to the output of the sensor 9 of the current installed at the input of the controlled rectifier 3, block 10 of the simulation of the controlled rectifier, is connected One of its inputs through the voltage sensor 11 to the input of the controlled rectifier 3, another input to the output of current regulator 8, and the output to one of the inputs of the first adder 12, the second input of which is connected to the output of the proportional-differentiating link 13. The output of the first adder 12 is connected to one of the inputs of the dividing unit 14. In addition, the electric drive has a master oscillator 15 connected by an output to the system input

Q

15

20 25 30

35

40

45

50

55

Themes 7 of the inverter control and the input to the output of the second adder 16, one of the inputs of which is connected to the output of the EMF sensor 17 of the induction motor 1, and the other input to the output of the phase regulator 18 connected by the first input to the output of the dividing unit 14, the regulator 19, connected by one of the inputs to the output of the intensity adjuster 20, the other input to the output of the frequency sensor 21, and the output of the frequency controller 19 is connected via the unit 22 to set the stator current module to the second input of the current regulator 8.

An amplifier-limiter 23, a filter 24 are inserted in the electric drive, and the amplifier-limiter 23 is connected between the output of frequency controller 19 and the second input of phase controller 18, and the filter 24 is connected between the output of the stator-current module setting unit 22 and the input of the proportional-differential link 13 , while the second input of the dividing unit 14 is connected to the code of the EMF sensor 17 of the induction motor 1.

An electric drive with a six-phase asynchronous motor contains an additional conversion section 25 (FIG. 2), made similarly to section 2 and connected to the second three-phase stator winding of an asynchronous motor 1. The phase regulator 18 is equipped with a third input connected to the output of a decoupling unit of the conversion section 25. the inputs of the conversion sections 2 and 25 are connected in pairs with each other.

As a possible option, the inputs of the converter sections 2 and 25 are connected to the mains through the secondary windings of a three-phase transformer 26 (with a star-star rt star-delta winding connection). The unit 22 for setting the stator current (a possible variant of its implementation) contains a rectifier 27 (FIG. 3) composed of two series-connected operational amplifiers 28 and 29, and a limiting unit performed at the comparator 30. The rectifier input and output 27 Lts, respectively, the input and output unit 22 of the task module of the stator current. The output of the Mittel 27 is connected through a resistor 31. The non-inverting input is 31

Parameter 30, the inverting input of which through a resistor 32 is connected to a source of positive bias voltage, and the output of the comparator 30 is connected through a series-connected diode 33 and a resistor 34 is connected to the input of an operational amplifier 29.

The limiting amplifier 23 contains an operational amplifier 35 (Fig. 4) in the feedback circuit of which the elements of limitation are included, executed in the form of transistors 36 and 37 and diodes 38 and 39, and the bases of these transistors are connected to sources of positive and negative, respectively polarity.

On the adjustment curves of the electric drive (Fig. 5), the following designations are accepted: 40 - curve I f (lg) of the transfer function of the unit 22 for setting the stator current module; 41 - curve cos if f (l) of the transfer function of the amplifier-limiter 23; 42 - curve 1y f (I) of the change in the actual value of the active component of the motor current 1 as a set value of the active component of the current lyi 43 - curve I., f (la) change of the actual value of the magnetizing component of the current I., as a function of the set value active component current 1,

In the vector diagram (fip.6) of an asynchronous motor, the following notation is taken: if is the generalized vector of the motor linkage, E is the generalized vector of the EMF of the engine J Ij is the generalized vector of the stator current; 1,1 - respectively active

"H

and the magnetizing components of the stator current; and - a projection of the generalized vector stator voltage and onto the generalized vector stator current Ig (proportional to the voltage at the input of the autonomous inverter); projection of the generalized vector EMF E to the generalized vector of the stator current is; (f is the angle between the vectors of the stator current and the emf.

The drive with a three-phase asynchronous motor (Fig.) Works as follows.

At the output of the intensity setting unit 20, a frequency setting signal f is input to the input of frequency regulator 19, where it is summed with the negative feedback signal f using the actual driving frequency

80

bodies coming from the sensor 21 frequency. At the output of the frequency regulator 19, a signal is generated for setting the active component I of the stator current of the motor, which is fed to the inputs of the block 22 for specifying the stator current module and the amplifier-limiter 23.

Unit 22 of the task of the stator current module (FIG. 3) generates at its output the signal I of the task of the engine stator current module in the form

1o, i; . I, I-cosc /;

(one)

J- - A-g-

where IP (0.1 - 0.15) is the minimum allowable value of the stator motor current, ensuring stable operation of the power circuit of an autonomous current inverter; I, cosi - nominal current values

and engine power factor.

At the input of the current regulator 8, the current reference signal I is summed with the negative feedback signal according to the actual value of the stator current modulus I, coming from the current sensor 9. The current regulator 8 acts through the control system 6 of the microphone on the angle of regulation of the tirkptorov controlled rectifier 3 converting section 2 in such a way that the actual value of the motor stator current is maintained at a given level: I I.

The amplifier-limiter 23 (figure 4) generates at its output a signal for setting the power factor

 . t t lo - (2)

cosi /,.

At the input of the phase regulator 18, the power g factor setting signal g is summed with the cos i / negative feedback signal based on the actual power factor value received from the output of the splitter unit 14. At the inputs of the adder 16, the signal from the output of the EMF sensor 17 and the signal

correction from the output of the phase regulator 18. Sensor 17 may also be implemented as a speed sensor. The output signal of the adder 16 is fed to the course of the master oscillator 15, which

513

through the inverter control system 7 sets the frequency (phase) of the output current of the inverter 5 so that the actual value of the power factor of the electric motor 1 is maintained at a given level: cos tC cos (f. In the case of the sensor 17 as a speed sensor, the correction signal from the controller output Phase 18 is a motor absolute slip signal. The external sensor 21 of the actuator may be configured as an output frequency sensor or motor speed sensor.

The inputs of the modeling unit 10 of the controlled rectifier, made, for example, in the form of a series-connected adder, functional converter and multiplier, receive signals from the output of the network voltage sensor 11 and the current regulator 8. At the output of the modeling unit 10, an analog signal is generated and

. proportional to the average value of the output voltage E, controlled by the rectifier 3, described by the expression

(3)

(four)

and

control

the input voltage of the controlled rectifier coming from the voltage supply sensor 11;

- the control signal of the system 6 of the pulse-phase control of the rectifier, coming from the output of the current regulator B.

The type of expressions (3) or (4) is determined by the shape of the reference voltage of the system 6 of the pulse-phase control, respectively, for a sawtooth or sinusoidal shape of the reference voltage. With a sawtooth support voltage, the functional generator included in block 10 has a characteristic of type cos, and with a sinusoidal reference voltage it has a proportional characteristic. A signal from the output of the simulated controlled rectifier unit 10 is fed to one of the inputs of the adder 12, where it is summed with the output signal and the proportional-differentiating link 13. In this case, the output signal of the proportional-differentiating link 13 is described by the expression

and i, (R,

e i

I (R

+ R

klMB

+ kk

S + Rdr) (5)

d A p

ke +).

current in the DC link,

0

Q

five

five

0

R

AR

niv

R. K AR

R R

the resistance of the smoothing throttle, the resistance of the inverter, taking into account the active losses in the inverter; active resistance of the motor stator winding i; coefficient of conversion of the load parameters to the DC link with respect to current; inductance of the smoothing throttle -,

time differentiation symbol; Rl „+ KR 5 - equivalent9 | In f, p ICH8

the active resistance of the choke, inverter, stator motor winding.

The input of the proportional-differentiating link 13 receives the signal I, from the output of block 22 of the task of the stator current module through the filter 24, which simulates the transfer function G (p) of the current control loop of the electric drive by the aperiodic link:

Ij (p)

(6)

Where

p + T

the time constant of the current control loop is small (it is assumed that the current loop is tuned to the technical optimum).

At the same time, the V-code signal of the filter 24, which is proportional to feedback on the actual value of the stator module of the motor, does not contain pulsations from switching processes in the rectifier, which, compared with the known electric drive, increases the noise immunity of the function of the proportional-differentiating link 13 and the proposed electric drive as a whole.

At the output of the adder 12, a signal is generated, described by the expression

“E, - I. (R, .e U specified signal U

pL, p). (7)

adder 12, proportional to the projection of the EMF E vector (Fig.6), and the signal of the EMF module

one

E, measured using the EMF sensor 17, is fed to the outputs of the dividing unit 14. At the output of the latter, a signal is generated that is proportional to the actual value of the engine power factor and is described by the expression

E,

cos Lf -.

(eight)

The output signal from the dividing unit 14 serves as a feedback signal on the actual value of the motor power factor for phase adjuster 18.

From the action of the flowing static currents in the phases of the motor (amplitude I and frequency f) in motor 1 a magnetic flux linkage i is created and an electromagnetic moment develops and, described by the formulas

If ID;

M flc. (9)

Under the action of the electromagnetic moment f, the electric motor 1 accelerates (decelerates) to a predetermined frequency value and then it is set to work at a given specified value of frequency f and the electromagnetic moment value equal to the moment of static resistance.

In the range of small values of the engine torque to which the signals for setting the active component correspond

,

ten

  - ctg h const. m

(12)

In the proposed drive, there is maintained a constant slip value equal to the nominal slip / engine, which means an economical law for controlling the engine with a minimum of losses and a constant power factor.

20 When the engine operates with large values of load torque (corresponding to 1 I,), in the proposed drive with an external frequency sensor, the speed of the engine stabilizes when the load torque on the motor shaft changes. This is accomplished by stabilizing the output 11 of the frequency of the electric drive (by means of a static proportional-integral frequency regulator 19) and automatically stabilizing the motor slip at a predetermined level (by a certain change in the flux coupling of the twofold current i to the output of the frequency regulator 19, taking into account - 35 "load moment functions,

corresponding to the mode of maintenance by the regulator 18 of the phase constant of the power factor of the engine). When the engine is operating with a large amount of electromagnetic moment in

electric drive through self-limiting output signal (Q)

frequency controller 19 is implemented

of the transfer functions (1) and (2) of the block 22 and the amplifier-limiter 23, the active and magnetizing components of the stator current of the engine are created:

1a I, COSL /;

Im lo

This means that in the range of small load moments, the change in the active and magnetizing components of the stator current of the motor is carried out, respectively, according to the sinusoidal and cosine laws (Fig. 5). At the same time, the stator current module I is maintained at a constant level of 1, which ensures stable operation of the autonomous current inverter at low engine loads.

In the range of large values of the engine number when the frequency of the active component of the current 1 is set by the regulator 19, taking into account the transfer functions (1) and (2)

current limitation of motor jg in motor and. generator modes

work (at level I

 1l / cos Y).

50

55

In block 22, the setting of the stator current module (Fig. 3) by means of the top of the taps 27, assembled on two operational amplifiers 28 and 29, the signal module lla is selected. Limiting the minimum output signal of the block 22 at the level I is performed by the node a limitation performed on comparator 30. The magnitude of the minimum magnetization current I o is determined by the level of the bias voltage -tU Q. The signal U is described by the following emulation:

The components of the stator current digger are as follows:

1 „And cos cos

IM

1 sin U n 5 (+.

(eleven)

In this mode, the engine runs at a constant slip value.

(eight)

ten

  - ctg h const. m

(12)

In the proposed drive, a constant slip value is maintained equal to the nominal slip / engine, which means an economical law of motor control with a minimum of losses and a constant power factor.

When the engine is operated with large values of load torque (corresponding to 1 I,), in the proposed drive with an external frequency sensor, the engine speed is stabilized when the load torque on the motor shaft changes. This is accomplished by stabilizing the output 11 of the frequency of the electric drive (by means of an astatic proportional-integral regulator 19 of the frequency) and automatically stabilizing the engine slip at a given level (by a certain change in the flux linking function of the load torque,

current limitation of motor jg in motor and. generator modes

work (at level I

 1l / cos Y).

0

five

In block 22, the setting of the stator current module (Fig. 3) by means of the top of the taps 27, assembled on two operational amplifiers 28 and 29, the signal module lla is selected. Limiting the minimum output signal of the block 22 at the level I is performed by the node a limitation performed on comparator 30. The magnitude of the minimum magnetization current I o is determined by the level of the bias voltage -tU Q. The signal U is described by the following emulation:

eleven

lo, i;

jldl

Cos ,,

WITH

The conditioner-limiter 23 (FIG. 4) generates at its output the signal U ,, about 1 expressed by the expression

, i; ,;

and,,

(14) 10

7

implementItcos c, I I J I

The limitation of the signal U is by means of the limiting nodes, made in transistors 36 and 37, to the bases of which voltage + and and - and jrp are applied, respectively. At the same time, the voltage + U corresponds to the limitation of the signal U in the motor mode of the drive (), and the voltage –Ug - to the limitation of the signal and, in the generator mode of the drive.

Electric drive with a six-phase asynchronous motor 1 (FIG. 2), i.e. having two identical three-phase stator windings, shifted in space by 30 e.grad., works as follows.

At the output of the intensity setting unit 20, a frequency reference signal is generated.

137258010

The steps of the dividing blocks 14 of the conversion sections (13) are 2 n 25. The adder 16, the output of which combines the signals from the outputs of the EMF sensor 17 of the motor and the phase regulator 18, sets the output frequency (via the master oscillator 15 and the inverter control system 7) of the autonomous Inverter 5 current converting sections 2 Jj25. By means of the converter sections 2 and 25, in the three-phase windings of the phase motor 1, two three-phase current systems are formed equal to

15 amplitudes (1 I) and frequencies.

As a result of the flow of stator currents through two three-phase stator windings in motor 1, magnetic flux coupling and electromagnetic torque are created according to expression (9), where IV, are the resulting flux coupling values and electromagnetic moment from the action of two three-phase stator windings. Electric motor 1

2B is accelerated (decelerated) to a predetermined frequency f, and then the mode is set at given frequency values and an electromagnetic momentum value equal to the static resistance.

received at the input of frequency regulator 19, where it is summed up with an electric drive (FIG. 2), is intended by a negative f signal. engines powered by you. At the output of the regulator 19 frequency

from individual three-phase frequency converters. In this case, the power circuits of the frequency converters are simplified, since a reference signal of the active component of the stator current 1, which is fed to the inputs of the amplifier - limiter 23 and the reference block 22 of the stator current module 22, is created without paralleling. I assigns a stator current module in three-phase windings of the engine 1 to the second inputs of current regulators 8 and the inputs of filters 24 identical to the conversion sections 2 and 25. At the output of regulator 18

The electric drive (Fig. 2) is intended to control powerful asynchronous motors created on the basis of six-phase motors fed

from individual three-phase frequency converters. In this case, the power circuits of the frequency converters are simplified, since they are created without parallel-connected thyristors, i.e. No complication of frequency converters using high voltage current dividers is required. Alignment of currents between converter

sections are carried out using current regulators 8 of the respective sections 2 and 25. To improve the harmonic composition of the magnetic flux curve in the air gap of six phases

phase, the reference signal of the cos factor gQ of the motor 1, and so for reducing the power coming from the output of the limiter amplifier 23, is summed with the sum of the signals of negative feedback cosi / power factor of each of the three-phase windings of the six-phase motor 1, signals of negative feedback according to the power factors of the three-phase motor windings, the pulsation of the resulting electromagnetic moment and the reduction of losses from the higher harmonic components of the current in the engine of the control system 7 are formed the inverter can be, alternatively, a pulse with a shift of the output control pulses 30 zl, hail, the output frequency, which provides a corresponding shift

30 el.grad. stator currents of the phases of three-phase motor windings 1.

Thus, the reduction of electrical losses in the electric drive is achieved by regulating the coupling of the engine as a function of the moment in order to comply with the economical control law with minimal losses in the engine. Compared with the known (in which the engine flux linkage is kept constant} -), the proposed electric drive (with an economical control law) provides a reduction of electrical losses of 7-10%, which creates significant energy savings in high-power electric drives.

An increase in the accuracy of stabilization of the speed of the electric drive (with an external frequency sensor) is achieved by keeping the load at a constant value (at the nominal level) of the engine slip by adjusting the flow of the engine as a function of torque. Due to the stabilization of the output frequency and the motor slip in the electric drive, the engine automatically stabilizes at a given level of rotational speed when the load torque on the motor shaft changes. In comparison with the known electric drive, the accuracy of stabilization of the rotational speed in the present invention increases by the value of the nominal slip, i.e. by about 2-3%.

I

In the proposed drive with

a six-phase asynchronous motor achieves an increase in power not due to the complexity of the converters themselves, but by performing the alignment of the currents between the converter sections by means of automatic control. Improving the harmonic composition of the magnetic field in the air gap, reducing the motor's electromagnetic torque ripples, and reducing engine losses from the higher harmonic components of the stator current are achieved by creating electrical inverter 30 electr. between currents. Supply three-phase stator windings of an electric motor.

formula

12

3 o

bratis

0

five

0

five

0

6

0

five

0

five

1. An electric drive containing an asynchronous motor connected by a three-phase stator winding to the output of the main converter section consisting of a series-connected controlled rectifier, a smoothing throttle and an autonomous current inverter, rectifier and inverter control systems, a current regulator connected by the output to the input the rectifier control system, and one of its inputs to the output of the current sensor installed at the input of the controllable rectifier, the simulator of the controllable rectifier, The first input is connected via a voltage sensor to the input of the controlled rectifier, the second input to the output of the current regulator, and the output to one of the inputs of the first adder, the second input of which is connected to the output of the proportional-differentiating link, and the output of the first adder is connected to one of the inputs of the dividing unit, the master oscillator connected by the output to the input of the inverter control system, and the input to the output of the second adder, one of the inputs of which is connected to the output of the EMF sensor of the induction motor, and the other input - with the output of the phase regulator connected by the first input to the output of the splitter unit, the frequency regulator connected by one of the inputs to the output of the intensity setter, the other input to the output of the frequency sensor, and the output of the frequency regulator connected via the reference unit of the stator current module with the second input of the current regulator, characterized in that, in order to improve the energy performance by reducing electrical losses and increasing the accuracy of the stabilization of the rotation frequency, an amplifier-limiter and a filter, And what is the limiting amplifier connected between the output of the frequency regulator and the second input of the phase regulator;

2. The electric drive according to i.1, about tl and - h and y with the fact that the additional converter section is introduced, is made similarly to the main one, the asynchronous motor is equipped with an additional three-phase stator winding, and the phase regulator is supplied with the third input, connected to the output

..

g

about

the dividing block of the additional converter section, the output of which is connected to the additional three-phase stator winding of the asynchronous engine, while the same-name inputs of both converter sections are connected in pairs to each other.

FIG. 2

+ GL

 la

srig.Z

37

l

.

.35

Ugz

fig L

i cos eio, ij, f

Cpi / Z.5

ff j f

(.6r) 4JUZ .6

Claims (2)

Claim 1. An electric drive containing an induction motor connected by a three-phase stator winding to the output of the main converter section, which consists of a series-connected controlled rectifier, a smoothing inductor and an autonomous current inverter, control systems for the rectifier and inverter, a current regulator connected to the input of the rectifier control system, and one of its inputs - to the output of a current sensor installed at the input of a controlled rectifier, a block of modeling a controlled rectifier, is connected the first input through the voltage sensor to the input of the controlled rectifier, the second input to the output of the current regulator, and the output to one of the inputs of the first adder, the second input of which is connected to the output of the proportionally differentiating link, and the output of the first adder is connected to one of the inputs of the dividing unit, the generator that is connected, the output to the input of the inverter control system, and the input to the output of the second adder, one of the inputs of which is connected to the output of the EMF sensor of the induction motor, and the other input is with the output of the phase regulator connected by the first input to the output of the dividing unit, the frequency regulator connected by one of the inputs to the output of the intensity regulator, the other input to the output of the frequency sensor, and the output of the frequency regulator is connected through the set unit of the stator current module to the second input of the current regulator , characterized in that, in order to improve energy performance by reducing electrical losses and increasing the accuracy of stabilization of the rotation frequency, an amplifier-limiter and a filter are introduced into it, moreover, The limiter is connected between the output of the frequency controller and the second input of the phase controller, and the filter is connected between the output of the reference unit of the stator current module and the input of the proportionally differentiating link, while the second input of the dividing unit is connected to the output of the EMF sensor of the induction motor. engine. 13 1372580 2. The electric drive according to item 1, with the fact that an additional converter section is introduced, made similarly to the main, the induction motor is equipped with an additional three-phase stator winding, and the phase regulator is equipped with a third input connected with the output of the dividing block of the additional converter section, the output of which is connected to the additional three-phase stator winding of the induction motor, while the inputs of the same converter sections of the same name are connected in pairs. FIG. 2. fi g. 4 FIG. 5