SU830628A1 - Device for control of semiconductor frequency converter - Google Patents

Description

(54) DEVICE FOR CONTROLLING A SEMICONDUCTOR FREQUENCY CONVERTER

one

The invention relates to electrical engineering and can be widely used in power supplies for induction electrothermal installations.

A semiconductor preamplifier & frequency frequency spreading device (VFR) is known that contains a power sensor, a comparison device, an amplifier, and a master oscillator, in which the frequency of the master oscillator determines the output frequency of the converter and its power 1,

The disadvantage of this device is the narrow power control range of the converter.

The closest in technical essence of the present invention is a device comprising a power sensor connected in series, a comparison device, the second input of which is connected to a reference signal source, an amplifier and a driving oscillator 2.

The disadvantage of this device is a narrow control range.

The purpose of the invention is to extend the adjustment range.

The goal is achieved by the fact that the device for controlling

The VFR containing a power sensor connected in series, a comparison unit, the second input of which is connected to a reference source, an amplifier and a master oscillator, is provided with a key, a sawtooth generator and a comparator, the first comparator input connected to the sawtooth generator

0 is the voltage, the second input is with the amplifier output, and the output is with the control input of a switch that connects the output of the master oscillator to a semiconductor frequency converter.

five

In addition, the sawtooth generator is made on an integrator to an impulse counter, the inputs of the integrator and the pulse counter are connected to the master oscillator, the output of the impulse counter is connected by the integrator reset circuit, and the output of the sawtooth generator.

FIG. 1 is a block diagram

5 of the proposed control device semiconductor frequency converter; in fig. 2 - typical dependence of the load power P on the frequency of the output current of the converter; in fig. 3 - curves, - for the following operation of the device; in fig. 4 is a block diagram of a sawtooth pulse generator; in fig. 5 - curves explaining the operation of the saw-tooth generator. The control unit of the frequency converter circuit (Fig. 1) contains a series-connected comparison unit 1, an amplifier 2 and a master oscillator 3. The output of the master oscillator 3 is connected via a switch 4 to the power frequency converter 5. The first input of the comparison unit 1 is connected to a reference signal source U, j and the second input is to the power sensor 6. The control input of the switch 4 is connected to the output of the comparator 7, one input of which is connected to the amplifier 2, and the second to the sawtooth generator 8. The control device operates as follows. The master oscillator 3 of the device generates a continuous sequence of pulses and (Fig. 3) whose frequency is a function of the voltage Uj at the output of the amplifier 2. When U2 decreases, the frequency of the pulses and the same decreases. The voltage Ua can vary in the range of 0 U2 $ U2rn. In this case, the frequency of the pulses of the driver master 3 varies within the limits corresponding to the frequency variations of the output frequency of the VFD in the range (Fig. 2.). The output voltage U, of the comparator 7 depends on the voltage Ug and U at its inputs for,, and, for, U —U-jjy ,. The key 4 is released in such a way that, when a voltage is applied at its control input, it is closed and the voltage and at its output repeats the voltage and, and at the voltage. The device (Fig. 1) is a closed system of automatic power control of the transducer. The signal from power sensor 6 is compared in block 1 as compared to the reference signal Uo. The difference between these signals is amplified by amplifier 2 and controls the frequency of oscillator 3. The device is designed so that using a load in the P, P $ range (Fig. 2) the amplitude signal Ug with FPG 8 is less than the voltage. In this case, the voltage of the comparator Uj, the key 4 is closed and the pulses and, the master oscillator 3 are fed to the control of the VFR 5 and their frequency determines the output frequency of the converter. Power control in the specified range is carried out by automatically changing the frequency of the driving oscillator 3 when the magnitude of the reference signal U changes. When the power of the signal amplitude Ug from the FPG is greater than the voltage U2 Let the voltage be in time (Fig. 3) U - the key is closed and the pulses Uj arrive at the control of the VFD 5. At. on time, so that Oug, the key 4 is open and the pulses and the master oscillator do not pass to the VFD 5 and it is turned off. At time t t2, the voltage Ug is again zero and the processes considered are repeated. The average power released in the load over time is equal to cf 1 51, (1) where P is the power of the VFD over time. Power control is made by changing the voltage U (j. This changes the error signal from the comparison device 1 and the output voltage and amplifier 2. This leads to a change in the time t. And in accordance with (1) the power. At reference voltage also equal to 0. Generator 8 sawtooth voltage of the device (Fig. 1) is made according to the scheme (Fig. 4), it consists of integrator 9 and pulse counter 10, the inputs of which are interconnected and connected to the output of the master oscillator 3. Pulse counter output - owls pods is connected to the integrator reset circuit, and the integrator 9 output is the output of the sawtooth generator and is connected to the switch 7 (Fig. 1). The integrator 9 can be performed, as shown in Fig. 4, based on the differential amplifier 11, resistor 12, the capacitor 13 and the reset circuit of the integrator 14. The integrator .9 integrates the pulses and the master oscillator 3 and its output voltage during the pulse duration t changes by the magnitude di. In the intervals between successive pulses, the voltage of the integrator U-5 is constant. Counter 10 divides the frequency of master oscillator 3. Therefore, the voltage is also on. its output is a sequence of pulses with a period pT, where T is the repetition period of the pulses of the master oscillator; n is the frequency division factor. Suppose that at the time the counter gives out a regular impulse to the integrator 14 reset circuit, and thereby performs the discharge of the capacitor 13 and the reset voltage of the integrator. At time t, the output voltage of the integrator is again zero and the process considered is repeated. Thus, the proposed device allows the control range to be expanded and the inverter power to be adjusted from nominal to zero by changing the reference voltage U

Claims (2)

1. A device for controlling a semiconductor frequency converter, containing a power sensor connected in series, a comparison unit, the second input of which is connected to a reference source, an amplifier and a master oscillator, which is different in that it is equipped with a key, sawtooth generator voltage and a comparator, the first input of which is connected to the saw-tooth voltage generator, the second input - to the amplifier output, and the output - to the control input of the key connecting the output d master oscillator with a semiconductor frequency converter. 2. Device by. Claim 1, characterized in that the sawtooth voltage generator is not connected to the integrator and the homing pulse counter, the integrator and pulse counter inputs are connected to the master oscillator, the pulse counter output is connected to the integrator reset circuit, and the integrator output is the saw voltage generator output . Sources of information 0 taken into account in the examination 1.Berkovich E.I. and others. Thyristor converters of high frequency. L., Energie, 1973, p. 165-170. 2.Vashkevich E.I. R.N. KiMov A system of control of an inverter of 250 kW with a frequency of 25,000 Hz using chips. Interuniversity scientific collection Thyristor frequency converters for induction heating of metal, No. 6 AIM, 1976, p. 49-53. H Pf - Rea P / nin fpt imin jtf fp, fig.g Fig.Z mmim.