RU1774453C - Method and device for starting induction motor - Google Patents

Abstract

Use in a thyristor electric drive in starting and ballast control devices for engines with a phase rotor. The invention consists in that the device is additionally equipped with a zero-element 9, an integrator 10, a threshold element 12, an element 3, a trigger 15. The time delay and amplifiers and provides increased reliability and performance. 1 s.p. f-ly, 3 ill.

Description

The invention relates to the field of electrical engineering and can be used in starting and ballasts of thyristor electric drives for motors with a phase rotor.

A known method of controlling a phase-rotor motor, as well as a device for its implementation by changing the starting resistors included in the rotor circuit.

The control method consists in maintaining, by means of an appropriate control algorithm, the excess moment of the resistance of the mechanism by a certain amount, which ensures the constant average acceleration during the start-up process.

The device that implements this method is a control station for the step change of series-connected starting resistances connected to the rotor of the engine with power switching equipment, which alternately bypasses these resistances.

The disadvantages of this technical solution are:

- insufficient smoothness of start-up, especially with changing load parameters of the mechanism;

- surges of current and moment when shunting starting resistances;

- low reliability of the device due to the presence of a large number of power switching equipment operating at significant current overloads.

The closest technical solution is a method of starting an induction motor by phase control of counter-parallel thyristors and series resistors, the resistance of which is changed during start-up and a device for controlling an asynchronous motor containing counter-parallel thyristors with a pulse-phase control system, a rotary synchronization transformer voltages, frequency adjusters connected to a rotary voltage synchronization transformer.

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The disadvantages of this method and device are the following:

- in the case of shunt thyristors, the device is implemented with a significant power of thyristors;

- when using shunt contactors and interrupting the current of the rotor with arcless switching, the acceleration rate decreases and the dynamic moments of the mechanism increase;

-shunting of the rotor by the contactor to exclude heat losses in the thyristors of the controller causes a mode of heavy current switching by the electromechanical device, which reduces the reliability of the device and the drive as a whole.

The aim of the invention is to increase reliability, speed and reduce weight and dimensions.

The essence of the method of starting the induction motor is that during acceleration, the rotor voltage is phase-regulated by counter-parallel connected thyristors with series-connected resistors, the resistance of which is changed using N groups of shunt contactors and the rotor voltage half-time T is measured / 2, compare it with a given value of tai and, when phase-wise, turn on the corresponding 1st group of bypass contactors (where NN-1 is an integer). In this case, at a time, the control pulses are removed from the thyristors for a time tewh and at T / 2 t on, the moment t0 of the transition of the rotor voltage through zero is determined and after a time T / 2-gV on, a signal is generated for the phase switching of the Nth group shunt contactors.

The combination of essential features of the method makes it possible to smoothly control the speed of the engine with minimal dynamic disturbance during shunts. turn on the electromechanical devices with a minimum pause in the current phase of the rotor and practically at low currents when shunting the rotor.

Fig. 1 is a functional diagram of a device for implementing a start-up method (shown for one phase), Figs. 2, 3 diagrams explaining its operation.

A device for starting an asynchronous electric motor 1 contains, in each of the m phases of the rotor winding of the electric motor, an acceleration circuit in the form of serially connected counter-parallel connected thyristors 2, 3 and two ballast resistors 4, 5, two shunting contacts with windings 6, 7 connected to

the outputs of the respective power amplifiers 8, 9 and make contacts 10, 11, and the contacts 10 of the first contactor are connected parallel to the first ballast resistor 4 and the contacts 11 of the second contactor are parallel to the entire acceleration circuit. The device also contains m control systems, each of which consists of a pulse-phase control unit 12, outputs

0 which is connected to the control circuits of thyristors 2,3, synchronization transformer 13, the input of which is connected to the terminal of the corresponding phase of the rotor winding, and the output is connected to the first input

5 block 12 of the pulse-phase control, speed control 14, connected to the second input of block 12, and two frequency sensors 15, 16 connected to the output of the synchronization transformer 13, zero 0 of the organ 17, integrator 18, threshold element 19, element And 20, trigger 21, time delay element 22 and diode 23. The output of the first frequency sensor 15 is connected to the first input of the element And 20, the output of which 5 is connected to the input of the second power amplifier 9. The input of the zero-organ 17 is connected to the output of the synchronization transformer 13, the first output is zero organ 17 through p consequently connected integrator 18 and threshold element 19. and the second output of the null organ 17 through the diode 23 is connected respectively to the second and third inputs of the element And 20. The output of the second frequency sensor 16 is connected to the input of the trigger 5 of 21, the output of which is connected directly to the input of the first power amplifiers 8 and through a time delay element 22 with a third input of the pulse-phase control unit 12.

0 The device operates as follows.

At the initial moment, thyristors 2, 3 do not conduct current due to the large values of the control angle of the pulse-phase unit

5 of the control (BIFU) 12, depending on the task of the unit 14, the control angle changes and the rotor current increases, which leads to an increase in the rotor speed.

0 When the set speed is reached, the frequency sensor 16 provides a signal to the trigger 21, which fixes this frequency and sends a signal to receive control pulses with a delay time,

5 of the contactor and half the period of the rotor frequency, which is provided by the delay element 22. At the same time, the trigger 21 sends a signal to turn on the first contactor through the amplifier 8. After the contactor is turned on, its block - contacts shunt the input

BIFU (removal of pulses), which restores control pulses and allows the engine to accelerate according to a new rheostatic characteristic. The circuit works similarly in the other two phases. Figure 2 shows the processes occurring in the phase of the rotor during operation of the first bypass contactor.

After executing the program of switching on all the first contactors in all three phases, the motor accelerates to a frequency when the half-cycle of the rotor frequency becomes longer than the switching time of the contactor and the circuit consisting of blocks 9.15-19, 20, 23 can enable the first bypass contactor to turn on. To explain how to turn on the contactor 8, see FIG. Logic element I20 will generate a signal to turn on amplifier 9 when three enable signals are received at its inputs. An enable signal is received at the first input when the frequency reaches a predetermined level, a signal generated from the operation of the zero-organ 17 (live) is supplied to the second input, which is converted into a triangular voltage shape (Uvykh) and compares with the set voltage Kzad determining the lead time, equal to the on time of the contactor t, On. At various frequencies higher than the frequency sensor reference 15, this lead time is kept constant, which allows the power contacts to be switched on with sufficient accuracy at the minimum instantaneous values of the rotor current in this phase. At the third input of element 13, the enable signal is received only at a certain voltage polarity of the rotor, corresponding to the falling part of the triangular voltage shape. When all three enable signals coincide at the input of AND element 20, an on-signal is generated equal to the on-contact voltage of the contactor.

Similarly, after switching on in the first phase, the switching on of the switching program in the other two phases is permitted.

The present invention provides the necessary acceleration rate and almost arc-free switching of electromechanical shunt devices, which increases the performance of the driven mechanism, reduces the total power of the thyristors and increases the reliability of the devices.

Claims (2)

1. The method of starting an induction motor, in which phase control of the rotor voltage is carried out by counter-parallel connected thyristors with series-connected resistors whose resistance is changed during start-up using N groups of shunt contactors, characterized in that, in order to increase reliability and speed, the half-period of the rotary voltage T / 2 is measured, it is compared with the set value t3i and at T / 2 tai turn on phase-by-stage the corresponding ith group of bypass contactors, while, when ON, the control pulses are removed from the thyristors by a time of Tcl - T / 2 at a time of t, 8 Kl, and when the time to the transition of the rotor voltage through zero and through time is determined T / 2-t.vkl fore they signal the phase-by-phase switching of the Nth group of shunt contactors, where is an integer. 2. A device for starting an asynchronous electric motor, comprising in each of the m phases of the rotor winding of the electric motor an acceleration circuit in the form of thyristors and two ballast resistors connected in series in parallel, two shunting contactors with windings connected to the outputs of the respective power amplifiers and closing contacts, moreover the contacts of the first contactor are connected parallel to the first ballast resistor, and the contacts of the second contactor are connected parallel to the entire acceleration circuit, and m s control circuit, each consisting of a pulse-phase control unit, the outputs of which are connected to the control circuits of the respective thyristors, a synchronization transformer, the input of which is connected to the terminal for connection with the output of the corresponding phase of the rotor winding of the electric motor, and the output is connected to the first input of the unit -phase control, speed controller, connected to the second input of the pulse-phase control unit, and two frequency sensors connected to the output of the synchronization transformer, distinguishing EU that. in order to increase reliability and speed and reduce overall dimensions, a zero-organ, an integrator, a threshold element, an AND logic element, a trigger, a time delay element and a diode are introduced into each control system, the output of the first frequency sensor is connected to the first input of the element, the output of which is connected to the input of the power amplifier of the second contactor, the input of the zero-organ is connected to the output of the synchronization transformer, the first output of the zero-organ through a series-connected integrator and threshold element, and the second course-body zero (Puzf i “k- .. (., po / ryOjO s - f Q . t V3 f v, f g