SU1210193A1 - Device for dynamic braking of induction motor - Google Patents

Description

to one input of the pulse generator, the output of which is connected to the input of the network thyristors control unit of the brake switch and to one input of the logic element 2I-NOT, the other input of which is connected to the output of the analog speed comparator controlling the input to the other input

I

The invention is related to electrical engineering and can be used in automated AC electric drives in which dynamic braking of induction motors registers.

The purpose of the invention is to increase speed and reliability.

The drawing shows a block diagram of the device.

The device for dynamic braking of the induction motor contains a power switch 1 included in the stator winding phases of the induction motor 2, a brake switch 3 composed of two mains 4 and 5 and a shunt 6 thyristor, the cathode of the first network thyristor 4 is provided with an output for connecting the first phase of the mains supply, the anode of the second mains thyristor 5 is provided with an output for connecting the second phase of the mains; the anode of the first mains thyristor 4 is connected to the anode of the shunt thyristor 6 and provided with a terminal for connecting the first phase winding 7 of the induction motor 2, the cathode of the second mains thyristor 5 is connected to the cathode of the shunt thyristor 6 and provided with a terminal for connecting the second phase winding 8 of the induction motor 2, the power control unit 9 of the braking speed, the output of which is connected to one the input unit 11 of the pulse-phase control of the brake switch 3, the outputs of which are connected to the control electrodes of the mains and shunt thyristors 4-6, unit 10

10193

the pulse generator and the control input of the control unit of the power switch, the output of logic element 2И-NOT is connected to the input of the shunt thyristor control unit, the output of which, together with the outputs of the network thyristor control unit, form the outputs of the pulse-phase control unit of the brake switch.

five

0

five

0

five

control braking speed is made in the form of a sensor monitoring the EMF of an induction motor 2, the input of which is connected to the third phase winding 12 of the induction motor

2, the pulsed-phase control unit 11 of the brake switch 3 is composed of an analog speed comparator 13, an analog pulse phase shift comparator 14, a matching unit 15, a logic element 2I-NOT 16, a delay element 17, a pulse former 18, control units 19 and 20 shunt and network thyristors 4-6, respectively, the input of the matching unit 15 is provided with leads for connecting the second and third phases of the supply network and forms another input of the block 11 of the pulse-phase control of the brake switch

3, the control input of the deceleration rate control unit 10 of the asynchronous motor 2 is connected to the blocking output of the power switch, one inputs of analog comparators 13 and 14 of the rotational speed control and phase shift of the pulses are combined and form one input of the block 11 of the pulse-phase control of the brake switch 3, the other the input of the analog comparator 11 of the pulse phase shift is connected to the output of the matching unit 15, and the output - to one input of the pulse former 18, the output of which is connected to the input of the network control unit 20 the aristocratic 4 and 5 brake switch 3 and to one input of the logic element 2I-NOT 16,

3

another input of which is connected to the output of the analog comparator 13 controlling the rotational speed and to the input of the delay element 17, the output of which is connected to another input of the pulse generator 18 and the control input of the control unit 9 of the power switch 1, the output of the logical element 2I-NOT 16 is connected to the input of the control unit 19 of the shunt thyristor 6, the output of which, together with the outputs of the control unit 20 of the network thyristors 4 and 5, form the outputs of the unit 11 of the pulse-phase control of the brake switch 3.

The device works as follows.

When the motor 2 is disconnected in the third phase winding 12 of the asynchronous motor 2, an electromotive force (EMF) is induced, the value of which is proportional to the speed of the motor 2. The specified electromotive force is applied to the speed control unit 10, rectified, matched to the pulse phase control unit 11, and then applied one of the inputs of the block 14 analog comparator phase shift pulses. Synchronous sinusoidal voltage shifted 60 forward with respect to the voltage on the braking switch network thyristors 4 and 5 is also fed to the input of block 14, therefore the maximum control angle of network thyristors 4 and 5 is 90. Shift pulse control braking on network thyristors

934

4 and 5 is carried out depending on the voltage of the EMF of the phase winding 12 in block 14. When the motor is stopped, the EMF of the phase winding I2 is zero and the braking is stopped.

When the braking is interrupted and the subsequent start-up of the motor 2, a signal from the engine controls 2 is sent to the input of the control unit 9 of the power switch 1, the signal from which the unit 10 is locked, its output becomes zero, the control pulses from the shunt thyristor 6 are removed, and on the network thyristors 4 and 5 is still present due to the delay element 17. The signal from the delay element 17 is also fed to the input of block 9, which prevents the switching on of the power switch 1 when the braking thyristors 4-6 are on. The last control impulse is applied to the network drivers 4 and 5, which means that the network is short-circuited during start-up and it is possible to interrupt the braking at any time without an exponential change of the dynamic braking current in the third phase winding 12 of the induction motor 2.

Thus, due to the separate control of the mains and shunting thyristors of the brake switch and control of the rotational speed of the induction motor according to the value of the EMF of the free phase winding, the speed and reliability of the device are increased.

Claims (1)

DEVICE FOR DYNAMIC BRAKING OF ASYNCHRONOUS MOTOR, containing a power switch included in the phases of the stator winding of the induction motor, a brake switch composed of two network and shunt thyristors, the cathode of the first network thyristor is equipped with a terminal for connecting the first phase of the supply network, the anode of the second network thyristor is equipped with connecting the second phase of the supply network, the anode of the first network thyristor is connected to the anode of the shunt thyristor and is equipped with an output for connecting the first phase windings of an induction motor, the cathode of the second network thyristor is connected to the cathode of the shunt thyristor and equipped with a terminal for connecting the second phase winding of the induction motor, a power switch control unit, a braking speed control unit, the output of which is connected to one input of the pulse-phase control unit of the brake switch, the outputs of which connected to the control electrodes of the network and shunt thyristors, characterized in that, in order to improve performance and reliability, the speed control unit the braking bridge is made in the form of an EMF control sensor for an induction motor, the input of which is connected to the third phase winding of the induction motor, the pulse-phase control unit of the brake brake <g mutator is composed of an analog comparator of rotation speed, an analog comparator of phase shift of pulses, matching unit, 2I-NOT logic element, delay element, pulse shaper, bypass and network thyristor control units, the input of the matching unit is equipped with leads for connecting the second and third phases of the supply network and forms another input of the pulse-phase control unit of the brake switch, the control input of the brake speed control unit of the asynchronous motor is connected to the blocking output of the power switch, one of the inputs of the analog comparators for controlling the rotation speed and phase shift of the pulses are combined and form one input of the pulse-phase block brake switch control, the other input of the analog pulse phase shift comparator is connected to the output of the matching unit, and the output SU, „, 1210193 to one input of the pulse shaper, the output of which is connected to the input of the control unit of the network thyristors of the brake switch and to one input of the logic element 2I-NOT, the other input of which is connected to the output of the analog comparator of speed control and to the input of the delay element, output which is connected to another input of the pulse shaper and the control input of the power switch control unit, the output of the logic element 2I is NOT connected to the input of the control unit of the shunt thyristor, the output of which о together with the outputs of the control unit of network thyristors form the outputs of the pulse-phase control unit of the brake switch.