SU1700738A1 - Frequency-regulated electric motor - Google Patents

Description

(21) i (706330/07

(22) 06/14/89

(46) 12/23/91. Bul (T 47 (70 Scientific and Production Association Rosavtomatstrom (72) S.I. Alekseev

(53) 621.313-333 (088.8)

(56) Avtooskoe testimony of the USSR if 1309247, cn, H 02 R 7/42, 1987.

USSR Author's Certificate number 1325656. cl. H 02 R 7/42, 1987.

USSR Author's Certificate No. 1264289, cl. And 02 P 7/42, 1986.

(54) FREQUENCY-ADJUSTABLE ELECTRIC DRIVE

(57) The invention relates to electrical engineering, namely, variable frequency drives, and is intended for use in general industrial systems and mechanisms with high demands on reliability and accuracy of rotation frequency stabilization. The purpose of the invention is to simplify and increase reliability. This circuit is reached by the th, the inverter control unit 15 is additionally equipped with a voltage multiplier 2k, a voltage sweep converter 25 and a sinus converter 26-28 ng. There is no rectifier control system m 3 and the control of the inverter 5 in the frequency converter 2 is simplified in comparison with the known solution. 6 yl

ha%

The invention relates to electrical engineering, in particular, to frequency-controlled electric drives, and is intended for use in systems and mechanisms for general industrial designation with high requirements for reliability and accuracy of rotation frequency stabilization.

The purpose of the invention is to simplify and increase h.

At Lig, 1, a functional diagram of a frequency-controlled electric drive is presented; on yig. 2 - investor unit management scheme; Fig. 3 is a schematic of a power converter; in fig. k is a diagram of the operation of a sinus voltage converter; in fig. 5 diagram of the operation of the voltage sweep; in fig. 6 - diagram of the drive.

The frequency-controlled electric drive contains an asynchronous motor 1 (see Fig. 1) connected by stator windings to the outputs of a speed converter 2 made of a series-connected uncontrolled rectifier 3, C-filter 4 and inverter 5. stator voltage sensor 6 , sensor 7 of the stator voltage frequency, tachogenerator 8, mounted on the shaft of the asynchronous motor 1. voltage regulator 9, slip regulator 10. three adders 11-13, a rotation speed setting unit 14 and an inverter control unit 15. Inverter control unit 5

P &

WITH

s

A voltage-frequency transducer 16 (see Fig. 2), a frequency divider 17, a phase converter 18 with three integrators, a pulse-width modulator 22 and a pulse shaper 23 are made with the outputs of which form the outputs of the inverter control unit 15. The inputs of the first adder 11 are connected to the outputs of the sensors 6, 7 of the stator voltage and the frequency of the stator voltage, and the output of the adder 11 is connected to the input of the voltage regulator 9. The inputs of the second adder 12 are connected to the output of the rotation frequency setting unit 14 and the output of the third adder 13 connected by inputs to the outputs of the sensor 7 of the voltage of the stator and the tachogenerator 8. The output of the adder 12 is connected to the input of the slip controller 10, the output of which is connected to the input of the voltage-frequency converter 16 connected via a frequency divider 17 with the input of the converter 18 phases. The first three inputs of the pulse generator 23 are connected to the outputs of the pulse-width modulator 22, and the fourth input is connected to the corresponding output of the phase converter 18. The inverter control unit 15 is additionally equipped with an analog voltage multiplier 2k, a potential voltage converter 25 and three sinus converters 26 -28 voltage. The inputs of the analog multiplier 24 voltages are connected to the outputs of the regulators 9, 10, voltage and slip. The output of the multiplier 24 is connected to the first input of a voltage sweep converter 25, the second input of which is connected to the output of a divider of frequency 17. Three other outputs of the phase converter 18 through the respective integrators 19-21 and sinus voltage converters 26-28 are connected to the first three pulses of pulse width a modulator, the quarters of which is connected to the output of a 25 voltage sweep converter. A voltage sweep converter 25 contains two voltage controlled sources 29, 30 (see FIG. 3) of positive and negative currents, two current switches 31 and 32, a capacitor 33 and an output repeater 34, the output of which forms a sweep output

five

0

five

0

five

0

five

0

five

voltage converter 25, and an input connected to one of the plates of capacitor 33 and the outputs of both current switches 31 and 32, one inputs of which, connected together, form the frequency input of a voltage sweep voltage converter 25 and the other input of each of switches 3.1 and 32 connected to the outputs of the voltage-controlled current sources, respectively, 29 and 30, whose inputs form the input 21 of the voltage sweep converter 25.

Variable frequency drive works as follows.

The Ug signal from the output of the tachogenerator 8 and the signal U7 from the output of the frequency sensor 7 arrive at the input of the adder 13, where they are algebraically added. The resulting signal U and the speed reference signal are fed to the input of the adder 12, in which they are compared and the error signal generated by the slip controller 10 is generated. The output control signal of the slip controller 10 is fed to the input of the control unit 15 by an inverter, which with a certain proportionality factor provides an increase or decrease in the frequency of the stator voltage, corresponding to a decrease or increase in slip, until the error is fully compensated. At the same time, the signal U of the stator voltage frequency, which sets the voltage level of the stator Us, from the output of the frequency sensor 7 and the signal from the output of the voltage sensor 6 goes to the inputs of the adder 11, in which they are algebraically summed. The error signal on the stator voltage is processed by the voltage regulator 9 to compensate for the error. The control signal Ug is fed to the input of the control unit 15 by an inverter, which provides such a regulating effect on the voltage inverter 5 that the latter increases or decreases the stator voltage linearly and with a certain transmission coefficient, corresponding to the increase or decrease in the stator voltage Ug.

The voltage of the stator U5 can be expressed in terms of the reference signal U, U7 with negative voltage feedback (see Fig. 1)

vvvCv-f-v-VKX.

where is the transfer coefficient of voltage regulator 9 at the direct input and feedback input, respectively;

Accept; into account that

we have

nQ i Ј

(d 514 5L0 KllKiO) -KiS

E-; () Kf0 Kj K | -

Q

four

one

Expression (1) taking into account the expression

one

b u

- coefficient of inverter 5; About for 7

- sensor transmission ratio - U7 K7 &) 6 K7 2ufs,

ka 6 stator voltage; where fg the frequency of the voltage the stat-transfer coefficient block-pa takes the form of control 15. n u u

15IT Kjj KiS K 5-.c

V 7-kgc LGKGk 211 and

Iff

Then

4J K (5 K 5

Similarly, the stator frequency Qs can ITIT - 1H s-IT

V TNGCKG; V

(ABOUT

  A6

From the expression (3) it follows

Us

P (J U Kg K15. K 5

K, - 27.

(four)

fs 1-к; -k-кц5-к6

20

but express it via the reference signal And with positive feedback on slip (see fig. 1)

about Ј i about, Ј i, 0-K K5 + io (h KHJ-K -KJ-,

no94 of the stator U5 from the voltage across the KW, K # is the transfer coefficient of the control UQ and the stator frequency Ј with an ohl of the torus 10 at the direct input and feedback input, respectively;

K (. Is the proportionality coefficient of the control unit 15;

KC- - inverter factor 5 Task signal. can express

thirty

fs 1-к; -k-кц5-к6

The pulse-width control system of the voltage inverter both produces a linear dependence of the voltage st;

the ratios and frequencies of the stator 5 of the control voltage, if the transmission coefficient K, 5 and the proportionality coefficient K are constant, do not depend,

mi from U, - and fc.- Therefore, the expression term (k) is a constant value that does not depend on Us and fs. Then the change in U5 is uniquely determined by the change in fs 35 in such a way that

and

J14

14

four,

hLe kN coefficient of proportionality of the setpoint1k; k)) 4 set frequency value

rotation

For the feedback signal we have

eight

here

ig k7-so5,

where C7 - coefficient of proportionality of the sensor 7; C05 - circular voltage frequency

stator; U8 KaCOr,

where Kd is the proportionality coefficient of the tachogenerator 8; CO is the frequency of rotation of the rotor. Then, taking into account the expressions for and, And, U, and Ug, we get

C05fЦ-А-кГо1 4 + (03к7-еэ, .к8) к, ° 0 х.

Accept; into account that

we have

nQ i Ј

(d 514 5L0 KllKiO) -KiS

E-; () Kf0 Kj K | -

Expression (1) taking into account the expression

IT Kjj KiS K 5-.c

V 7-kGk LGKGk 211 A6

From the expression (3) it follows

Us

P (J U Kg K15. K 5

K, - 27.

20

(four)

94 stator U5 from the control voltage UQ and the stator frequency Ј with

thirty

fs 1-к; -k-кц5-к6

The pulse-width control system of the voltage inverter ensures the linear dependence of the voltage st;

and the stator frequency 5 and the control voltage, if the transmission coefficient K, 5 and, the proportionality coefficient K are constant values, do not depend on U, -, and fc. Consequently, the expression (k) represents constant value not dependent on Us and fs. Then the change in U5 is uniquely determined by the change in fs 35 in such a way that

ensures the maintenance of a constant magnetic flux of the asynchronous machine in the whole range of rotor frequency control CDr. From expression (2) it follows that the pulse width control system of the voltage inverter provides a linear dependence of the COS frequency of the stator voltage Us on a given slip C0, c. if the coefficient of proportionality and the coefficient of the inverter circuit are H & are constant values independent of Ug and fs. Consequently,

40

50

(five)

five

g - (

 ссо μ; -к к - к1-к |

Regulation of the frequency of the stator voltage in the electric drive under consideration is carried out using positive feedback on the slip with an effect that is not consistent with the frequency of the voltage of the torus. From expressions (k) and (5) it follows that the frequency control under consideration provides cost-effective control of an asynchronous motor by adjusting its flow with a constant slip value. In the control unit 15 of the voltage inverter 5, the input signal enters the input voltage-frequency converter 16, which provides a linear dependence of the output frequency f (6 on the level of the input control voltage Uf0

 o

where K, | Ј-- coefficient of proportionality.

The pulse sequence is further subjected to digital processing by a dividing unit 17, which is a symmetric with a duty ratio 2, an input pulse divider with an even division factor of N

,

where n is any integer (). Then

17007388

ow f 47 with an even division factor,

satisfying the condition

f17b10f, 8, where

ten

15

20

25

7 frequency modulated signal;

inversion frequency or carrier frequency,

so that the output modulated signal is equal in amplitude and frequency of the envelope voltage to the input modulated signal with the required accuracy.

Therefore, taking into account (6)

f Јi7-2q 4nq

U

(ABOUT

where q is any number (q; 5).

The output signals of the phase converter 18 f {g, f, 8, f, having the form of a meander with a duty cycle of 2 and a constant amplitude of U18, go to integrators 10, 20 and 21, which convert them into triangular signals of the same frequency

U4, -K, yuJ,, U20 -K20-U18,

U2 -K2, UW, where, yoke, U2l- output amplitudes

b 2n

  Q

- K11 t,

2n

(6)

 De f

"7

output frequency of the pulse train of the dividing unit 17.

The output of the division unit is fed to one of the inputs of the voltage sweep converter 25 and to the input of the phase converter 18, which is designed to automatically save the phase of the inverter output voltage.

pulses of the fundamental modulation frequency f.an, fk s f so that

48

"but

€ D f MS s 18 fb fc, -Ь18 t18

1. Gives continuous parallel along three channels a, b and c (according to the number of inversion phases) sequential

ti

2. Continuous shift of output im d f b fc

, t Г, HU HdtldJldM d, (

pulses €, g, f ®a, f ig through channels a

Vis respectively on 0, 120 and.

3. Continuous symmetric with a duty ratio of 2 division of the input pulses satisfying the condition

f17b10f, 8, where

five

7 frequency modulated signal;

inversion frequency or carrier frequency,

so that the output modulated signal is equal in amplitude and frequency of the envelope voltage to the input modulated signal with the required accuracy.

Therefore, taking into account (6)

f Јi7-2q 4nq

U

(ABOUT

0

five

0

where q is any number (q; 5).

The output signals of the phase converter 18 f {g, f, 8, f, having the form of a meander with a duty cycle of 2 and a constant amplitude of U18, go to integrators 10, 20 and 21, which convert them into triangular signals of the same frequency

U4, -K, yuJ,, U20 -K20-U18,

U2 -K2, UW, where, yoke, U2l- output amplitudes

integrator voltage 19-21;

five

equivalent gains; the amplitudes of the output signals of the converter 18. Since

 2o (840

because

 ,

tta tt

U18 U1S

eight

45

that

UTO -K "e-U, 8.

(cm.

(9)

(ten)

where - the period of the pulses of the modulated frequency; C0 (& - circular frequency of pulses

modulated frequency. Substituting (8) and (10) into (9), we have

uTp (t) U signals.

2K9Kb 1Le

C0tat.

(eleven)

and.

and U.,

  U2o and U2i are fed to the inputs of the corresponding sinus voltage transformers 26-28, designed to automatically maintain the sinusoidal shape of the output voltage of the inverter, when measured, which are determined by the level

load (see Fig. k). A sine converter is designed to implement the expression

the input voltage, depending on the polarity of the pulses, is connected to the capacitor for charging and discharging, forming triangular pulses with often Ј17 and amplitude determined by Uzs

WO-n.Jnff.1

Mr. J

(12)

in the range of input voltage

(b) IT

2 ™ e isii f ° tr

Substituting (8), (11) tea

Wt) e - if

sin (cOIAt). (l3)

Consequently:

U26 (t) - | K9K6-U, 8.sin (cOt8t), U27 (t) - | K3K6-U18sinto, 8t + 120 °), U2g (t) - / z K3j, sin ((0 ().

The signals U2, iG, Ugg are designed to receive at the outputs a, b and c of the pulse-width modulator 22 a sequence of pulses with a frequency f17, the width of which would change in accordance with the change of the modulated voltage, and sinusoidal. Another signal U9 from the output of the voltage regulator 9 arrives at one of the inputs of the analog voltage multiplier 2k, to the other input of which a signal comes from the output of the sliding regulator 10.

Those. .Ug.U (0, (14)

where is the proportionality coefficient.

700738L °

The output signal U2 of the analog voltage multiplier 2k is the input to the voltage sweep converter 25, which performs the voltage sweep and frequency signal ff7 (see FIG. 5) The 2f square-wave input signals, symmetrical with a duty ratio 2 f, control at a frequency ff Such switches 31 and 32 (see Fig. 3), through which the sources 29, 30 of positive and negative currents controlled by the input voltage U24, are equal to 10

which are determined by the level

the input voltage, depending on the polarity of the pulses, is alternately connected to the capacitor 33 for charge and discharge, thereby forming triangular pulses at the output of the unwrapping converter with a frequency of ~ 17 and an amplitude determined by the Uzs-.

The capacitance of the capacitor 33 is determined

with to - - Chz ks and zz

Then the voltage across the capacitor Uj9

thirty

TT-TT - T T -7 / ---

izz iez "Szz

(15)

Where

 charge of capacitor 5; Kc - proportionality coefficient; U jUjjj - potentials of quince plates

capacitor 33.

The capacitor charge, when the latter is charged or discharged by a constant current, is expressed as

.

(sixteen)

where KQ is the proportionality coefficient;

t is the charge or discharge time; I is the discharge or charge current. Here takes place)

The charge or discharge time of a capacitor, provided that the duty cycle of the control switches 31 and 32 of the square-angle pulses is equal to 2, is determined by the expression

t, II-12f

(7

(17)

where is the period of control pulses with frequency

The magnitude of the current charging and discharging capacitor 33 is a linear function of the control current source voltage is determined by the expression

zhz-i-k -, - k24-i9-yu, (18)

where K. is the proportionality factor of current sources 31 and 32.

Then the amplitude of the output voltage of the sweep converter, taking into account (6), (17), (15), (18), is

(t), K3,

P IT

 g- U9 C 35 7

where .- transfer coefficient. Consequently

U2f (t) Cu-U9, (19)

here is a constant coefficient

Кз4 Кс Ke-Kr KZ4 П

V

TO

sixteen

 33

The right part of the last expression is constant and does not depend on the control voltage and „and the frequency ft7. Therefore, the level of output triangular pulses with frequency f, which are the carrier for modulated signals, U and U2B, is uniquely determined by a linear dependence on the control voltage a stator voltage regulator (see FIG. 6}.

Then, with a constant inversion ratio

With fs.

B, f 18

where q 5,

the average value of the voltage on the load will vary sinusoidally

Un

UH 5- | U.einQ9t,

(20)

where U fj is the voltage value of the power source;

5 Circling modulation frequency; / K is the modulation depth factor,

which shows the extent to which the durations of the open and closed state of the power half-layers vary

five

0

five

0

five

0

five

inverter voltage regulators for a period of modulation frequency. From expression (20) it follows that the value of the parameters D | l f, it is possible to independently control the amplitude and frequency of the stator voltage with a constant inversion coefficient and a constant supply voltage. Pulse width modulator 22, the inputs of which are a, b and c are sinusoidal voltages, Uj / j. and setting the sinusoidal shape, phase and frequency of the stresses on the stator windings of the asynchronous electric motor modulates these voltages with the carrier frequency of the three channels a, b and c The pulse shaping unit 23, synchronized from the phase conversion unit -; 18 generates control pulses for the voltage inverter 5. By expression (20), the modulation depth can be changed: by adjusting the amplitude of the modulated sinusoidal signal at a constant amplitude of the inversion frequency; by adjusting the amplitude of the inversion signal (carrier frequency signal) at a constant amplitude of the modulated sinusoidal signal. To avoid overmodulation, the amplitude of the input signal should not exceed the amplitude of the triangular voltage carrier frequency.

According to expression (19), amplitude is. And the triangular carrier voltage is changed by voltage regulator 9. Then at a constant level of modulated sinusoidal voltage U26, U27 and U2g on the input of the modulator 22, determined only by the voltage, the average voltage on the load is proportional to the voltage management do. From the expression (7)

4nq

 or

(21)

 ,

here GЈ is a constant coefficient

Mr. SG 5nq 7

those. the value of the frequency of the voltage of the stator varies linearly with the dependence on the voltage level at the output of the slip controller 10. Therefore, it can be concluded according to the expressions (:), (19) and (21) that in a closed system with two flow stabilization circuits and rotational frequencies, it is possible to obtain a wide frequency control range with a high overload capacity with a simpler, therefore more reliable frequency converter control circuit in comparison with the known solution.

Claims (1)

Invention Formula A frequency-controlled electric drive containing an asynchronous electric motor connected by stator windings to the outputs of a frequency converter made of a series-connected uncontrolled rectifier, a C-filter and an inverter, a stator voltage sensor and a stator voltage frequency sensor, a tachogenerator mounted on an asynchronous shaft electric motor, voltage regulator, regulator of slip, totalizer frequency, frequency setting unit and inverter control unit, made with voltage converter a sine frequency, a frequency divider, a phase converter, three integrators, a pulse-width modulator and a pulse shaper, whose outputs form the outputs of the inverter control unit, while the inputs of the first adder are connected to the outputs of the stator voltage and stator voltage frequency sensors, and you - the course of the first adder is connected to the input 5 10 $ n 5 0 five the house of the voltage regulator, the inputs of the second adder are connected to the output of the speed setting unit and the output of the third adder connected by inputs to the outputs of the stator and tachogenerator voltage frequency sensors, and the output of the second adder is connected to the input of the slip regulator, which is connected to the input voltage-frequency converter connected via a frequency divider to the input of the phase converter, the first three inputs of the pulse shaper are connected to the outputs of the pulse-width modulator, and the fourth input - to the corresponding output of the phase converter, characterized in that, in order to simplify and increase reliability, the inverter control unit is additionally equipped with an analog voltage multiplier, sweep voltage converter, and three sinus voltage converters, while the inputs of the analog voltage multiplier are connected to the outputs of the voltage and slip regulators, the output of the analog voltage multiplier is connected to the first input of a voltage sweep converter, the second input of the The other three outputs of the phase converter are connected via the appropriate integrators and the sinus voltage converters to the first three inputs of the pulse-width modulator, the fourth input of which is connected to the output of the voltage sweep converter. T v SNfc 15 19 25 22 23 Sh 20 27 -O G71 Pc g 27 and 25 BUT 16 P  ten eight Fig1 0 Fi.Z J OS ( about g-- I S