SU1325653A1 - Frequency-controllable electric drive - Google Patents

Abstract

The invention relates to electrical engineering and can be used in various areas of industry, in particular in vehicles. The aim of the invention is to increase the intensity and decrease the braking time. This goal is achieved by introducing a braking current regulator 14, a braking current sensor 15, a regulator control unit 16 into a frequency-controlled electric drive. Regulator 14 is connected between the middle lead of the braking resistor 8 and the output of the inverter 2, and its control input is connected to the output block 16. The inputs of block 16 are connected to the outputs of sensor 15, block 10 for setting operating modes, sensor I3 of flow and sensor 7 of rotational speed. The electric drive allows to increase the braking force in the entire frequency range, to reduce the wear of the parts of the mechanical brake. 2 Il. g. t (P d to

Description

one

The invention relates to electronics and can be used in various fields of industry and transport, in particular on vehicles with asynchronous short-circuited motors and inverters.

The purpose of the invention is to increase the intensity and decrease the braking time.

FIG. 1 is a schematic diagram of a frequency-controlled electric drive; in fig. 2 - its brake characteristics.

The variable frequency drive contains an asynchronous motor 1 with a short-circuited rotor, the stator winding of which is connected to an inverter 2, whose input is connected to a controlled rectifier 3 (voltage regulator, Fig. 1), unit 4 for controlling the voltage regulator in mode T ha and Braking of the induction motor, the inverter control unit 5 in the T mode, and Braking, the output of which through the adder 6 is connected to the control input of the inverter 2, the second input of the adder 6 is connected to the rotational speed sensor 7, the brake resistor 8 An average output connected via a control key 9 parallel to the input of the inverter 2, a mode setting unit 10, three outputs of which are connected respectively to the control inputs of the control unit 4 of the voltage regulator 3, the inverter control unit 5 and the control key 9 " Sensor 1 i current and sensor 12 for example. They are connected to the inputs of blocks 4 and 5 of the voltage regulator and inverter control, the flow sensor 13 and the rotation frequency sensor 7 are connected to other inputs of the inverter 2 control block 5, the braking current regulator 14 consists of three thyristors, the anodes of which are combined and connected The average output of the braking resistor is 8, and the cathodes are connected to the output of the inverter 2. The electric drive also contains a braking current sensor 15, a braking current controller control unit 16 composed of a series-connected comparator 17 controlled by a key and 18, the control system 19 by said thyristor regulator 14, braking current. The input of the comparator 2 is connected to the flow sensor I3 and the brake current sensor 15

0

five

0

five

3, and the control switch 18 is connected to the auxiliary output of the mode control unit T ha and Braking.

The drive works as follows.

Block 10 sets the required mode of operation of the drive. In the traction mode, block 10 receives the command: B blocks 4 and 5 of the control and control keys 9 and 18 for restructuring the drive circuit. In this case, in block 4 of the control of the voltage regulator in the mode of T ha and Braking with the key 20, the control of the regulator 3 of the voltage switches to the control of the mode T ha. At this voltage, the asynchronous machine is formed by setting the duration of the control pulses generated in the voltage control unit 20 in the mode T ha of the control unit 4 and fed through the switch 21 and the system

22 controls to the control input of the voltage regulator 3.

A similar switching occurs in the inverter control unit 5. A signal proportional to the slip frequency f is generated in the block.

23 Inverter control mode T ha. Through key 24 he enters

an adder 6, where it is summed with a signal fp proportional to the frequency 5 of rotation of the asynchronous mask 1 formed by the sensor 7 of the rotation frequency. At the output of the adder 6, a signal is generated, which is proportional to the frequency of the inverter 2 f, fed into the control system 25 for generating control pulses. In this case, the equality

0

0

five

f, fp ± f

H

II 1 and

S

+ corresponds to t govom -

where is the sign

mode, and - - braking mode. At the same time, the control key 9 disconnects the brake resistor 8 from the power circuit, and the control key 18 in

50

block 16 excludes the supply of pulses by the control system 19 to the thyristor control electrodes. Testing and braking characteristics of the frequency-controlled electric drive for- mation of 55 RUYuts in the control unit 3 of the voltage regulator 3 (voltage setting of the induction motor 1) and inverter 2 (voltage setting of the stator current of the induction motor 1) using

CHI narioB feedbacks on current, rotational frequency, magnetic flux and voltage of an induction motor.

The limiting characteristics are also formed by blocks 4 and 5, in which the feedback signals are compared with the setpoint signals — transform values of y1, numerical parameters,

The re-drive of the electric drive to the braking mode is carried out, as in the traction mode, by block 10 with the help of structural adjustment of the power circuit and control system.

In this case, with the help of the key 21, the voltage regulator control unit 4 switches to the operation mode from the voltage control unit 26 in the brake mode. This unit excites the induction motor at the initial moment and maintain a stable self-excitation of the induction motor I in the process of resistor braking,

The key 9 is the brake resistor 8 on-25 of the moment having the smallest

value at maximum frequency

into the power circuit of the electric drive. At the same time, the inverter control unit 5 using the key, 24 switches to the operation mode from the inverter control unit 27 in the brake mode, at the output of which a negative slip signal is generated.

The closure of the control key 18 connects the block 16 of the control regulator of the braking current to the common control system.

The limiting braking characteristic M- (f; i) and the law of voltage variation at the input of the inverter and magnetic flux as a function of frequency U (j (f) and F (.) Are shown in Fig. 2 for the case when the regulator 14 of the braking current and block 16 is absent. The characteristic of the brake (active) current of the induction motor 1 1 e (), corresponding to the law of change llj (f,) under the same conditions, is also shown there.

FIG. 2 also shows the characteristics of the electric drive when regulating the braking current using blocks 14 and 16: Ig (f) - braking TOKaj M () - braking torque; Kj (f,) is the coefficient of the brake current regulator as a function of frequency f.

thirty

value at maximum frequency

In order to increase the braking efficiency, the thyristors of the braking current regulator 14 are periodically switched on with simultaneous delivery of a continuous pulse to all three thyristors. When changing the duration of these control pulses, the equivalent braking resistance R

TEKV

smoothly changing ot

RT (impedance 35 of resistor 8) to a value equal to

0.5R with constant thyristors of the regulator 14.

At the same time, two signals are compared at the comparator 17 of the control unit 16 for controlling the braking current regulator: from the magnetic flux sensor 13 and the braking current sensor 15 W. Each of these signals characterizes 45 respectively the flux and the active component of the total current of the asynchronous motor. The drive control system in the voltage limited zone maintains the equality of these 50 components. In this case, the braking torque value of the asynchronous motor 1 is formed, which is close to the critical torque value. It happens

spedunitsim way. With frequency q,

Characteristic (f) corresponds to 55, the value of the magnetic flux

 This value of the flow will correspond to a certain value of the active current. At the same point, in the absence of a regulator, 14 brakes the characteristic of the critical moment of the asynchronous machine.

From the frequency f 0 to j, the magnetic flux is limited

five

0

asiEchronous motor 1, and at frequencies from f, 5 to f µs the voltage limitation (asynchronous motor 1 or voltage inverter 2), where f ,, is the maximum frequency of the stackMix

Torah.

The resistance value R of the braking resistor 8 is determined based on the ratio

, at "o1ks

where is the maximum voltage of the inverter at the input; the maximum active current through the braking resistor 8 at the maximum speed of the asynchronous machine.

The maximum value of the current is limited either by the allowable current of the inverter 2, or by the highest temperature of the resistor 8, or by the critical value

poppy

oro of the moment having the smallest

the value at the maximum frequency, the increase in the efficiency of the traction, periodically switches on the thyristors of the brake current regulator 14 with simultaneous application of a continuous pulse to all three thyristors. When changing the duration of these control pulses, the equivalent braking resistance R

TEKV

smoothly changing ot

RT (impedance of resistor 8) to a value equal to

0.5R with constant thyristors of the regulator 14.

At the same time, two signals are compared at the comparator 17 of the block 16 for controlling the brake current regulator: from the magnetic flux sensor 13 and the braking current sensor 15 W. Each of these signals characterizes a flux and an active component of the total current of the induction motor. The drive control system in the voltage limited zone maintains the equality of these components. In this case, the braking torque value of the asynchronous motor 1 is formed, which is close to the critical torque value. It happens

current value of the active component I .. f will be determined in

° 1 "" his

The main value of the resistor braking resistor R. In order to increase the braking moment to a value close to the maximum value, the braking current controller 14 adjusts the braking current (active current) at which the equality U

“Ki. where uj

1ms1 "(" s;

- and Shoks Zf - signals

I 1 "" M

from sensors of active current and agitated flow at the maximum rotation frequency of the asynchronous machine; K - coefficient of proportionality, ensuring the equality of these signals at

frequency

1Ms1ke

Wits are larger than the signal from the sensor 5 of the braking current of the current; This results in a signal from the output of the 17p comparator control system 9, allowing the formation of control pulses by the thyristors of the 1D controller, the thyristors are opened, and the braking current begins to increase. At 4vn time, the signals of the sensors 13 and 15 become equal to Uj J -Kif. At the output of the comparator 17, the signal is equal to zero, the supply of control pulses to the controller 54 by the control system 19 is stopped. After a period of time, the whole process is repeated. With a further decrease in the frequency f, the fill factor of the controller increases.

The condition for obtaining the maximum

FIG. 2 point with

moment.

when an asynchronous machine with a constant 20 | Yes active current, and K.

-.J -1 | ioke (, ..-.

Between the points c and a, the Mt (.1,) curve of the braking torque generated by the electric drive is maximally close to the characteristic

The voltage U is its proportionality to the square of the magnetic flux; On the other hand, the braking moment is determined by the magnitude of the active current 1d and the magnetic flux F: K / -F-Xd. Consequently, when forming the characteristic I (f according to the law of change in the flux of the asynchronous machine F (), the characteristic of the braking torque m. (.) Will be as close as possible to the characteristic of the critical moment M (f,).

In the absence of a braking current regulator 14 in the frequency range where V constj is the active current I, const. With the help of the controller 14 and the control unit 16, the equivalent braking resistance RT-JKB can be changed t D 0 t sam1) W to form the braking characteristics

M; (f) and i; (f,).

At the maximum frequency., D (the overload capacity of the asynchronous machine is determined

 ,with

iwanc

MT

1 MI "

MT MT. “.., -.„. I t-f "n" vc G1 "ax

By lowering the frequency f

Wherein ,

The controller 14 comes into action. Its operation is characterized by the filling factor of the brake current regulator 14, / T, where t is the capacity of the thyristors controlling the regulator; T is the period of the frequency with which the regulator operates. At,., D. In the process of reducing the speed of the signal from the sensor 13 current V, become

Wits are larger than the signal from brake current sensor 5K. This leads to a signal coming from the output of the 17p comparator control system 9, allowing the formation of thyristor control pulses of the 1D controller, the thyristors are opened, and the braking current begins to increase. At 4vn time, the signals of the sensors 13 and 15 become equal to Uj J -Kif. At the output of the comparator 17, the signal is equal to zero, the supply of control pulses to the controller 54 by the control system 19 is stopped. After a period of time, the whole process is repeated. With a further decrease in the frequency f, the fill factor of the controller increases.

FIG. 2 point with

moment.

active current, and K

When | | Yes active current, and K.

-.J -1 | ioke (, ..-.

Between the points c and a, the Mt (.1,) curve of the braking torque generated by the electric drive is as close as possible to the critical

braking torque).

As the speed decreases to the frequency f, u, the braking torque continues to increase due to an increase in the magnetic flux, and when d- decreases due to

a decrease in the braking current of the asynchronous machine due to a decrease in the voltage Uj.

Thus, the abcdf figure limits the additional range of braking torque values that the electric drive allows to produce.

The invention allows to extend the range of electric braking, reduce the wear of mechanical brake parts, increase vehicle safety and vehicle performance by increasing the intensity and reducing the braking time.

Claims (1)

Invention Formula Variable frequency drive containing an asynchronous motor 50 a frequency converter made as a series-connected controlled rectifier and an inverter, the output of which is connected to the stator winding of an asynchronous motor, a brake resistor connected via a control key to the input of the inverter, a flow sensor and a rotational speed sensor of the asynchronous motor, current sensors and for example /13 neither in the power supply circuit of the induction motor, the control units of the rectifier and the inverter, the adder, one input of which is connected to the rotational speed sensor of the asynchronous motor, the other to the output of the inverter control unit, a. the output of the adder is connected to the control input of the inverter, the outputs of the current, voltage, flow and rotation frequency sensors are connected to the corresponding inputs of the inverter control unit, and the inputs of the rectifier control unit are connected to the outputs of the current and voltage sensors, the task setting unit, the outputs of which are connected to the control inputs of the rectifier and inverter control units and the aforementioned key, characterized in that, in order to increase the intensity and decrease the deceleration time, the current regulator is decelerated 3 eight The braking current sensor connected in series with the braking resistor, the braking current regulator control unit, the braking resistor is made with an average output, and the mode setting unit has an additional output, while the braking current regulator is made in the form of three thyristors, the anodes of which are combined I - are connected to the middle output of the braking resistor, and the cathodes are connected to the outputs of the inverter, - the control unit of the braking current controller is composed of series-connected comparator controlled by the key and the control system of the said braking current controller drivers, the inputs of the comparator are connected to the flow sensor and the braking current sensor, and the control key is connected to the auxiliary output of the operating mode drop unit. Ud Mr F, wf 1a Ta /// / S- /  X. Ua UdMOKe G.Gerber / W Co: tavitel A.Golovchenko Tehred L. Serdyukova Order 3122/53 Circulation 659 Subscription VNIIPI USSR State Committee on inventions and discoveries 113035, Moscow, F-ZZ-Raushsk nab, d. 4/5 Production and printing company, Uzhgorod, ul. Proektna 4: AMMt Proofreader N.Korol