SU1443097A1 - Method of controlling frequency converter with d.c. link - Google Patents

Abstract

This invention relates to electrical engineering and can be used in frequency converters. The purpose of the invention is to increase the reliability of the converter. In the converter control method, the product of the output parameter and the alternating voltage is integrated and the stored value of the integral is summed with the frequency setting signal of the inverter. The resulting signal is converted to a control pulse frequency. As the output parameter, the difference between the measured output capacitance and the limit signals is used. Limit signals are formed at positive values of the differences of the measured limited parameters and their allowable 5 levels. 2 Il. cl

Description

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The invention relates to electrical engineering and can be used to control converters of technological processes using, for example, induction heating.

The aim of the invention is to increase the reliability of the converter,.,

FIG. 1 is a schematic diagram of a device implementing a control method; in fig. 2 is a diagram of the signal changes at the outputs of individual circuit nodes in the control process.

The device contains a control generator 1, a distributor 2 pulses of control of the inverter valves, a sensor 3 of the output parameter, a multiplier 4, an adder 5, a filter 6, a counter 7, a decoder 8, an integrator 9 with zeroing and storing input, a block IO of storing and storing information and clocking inputs, a control unit of a rectifier containing a synchronizer I, a sensor 12 of a limited parameter, comparison blocks 13, multiplication blocks 14 and an adder 15. The converter consists of an inverter 16 and rectifier 1 7. The output of sensor 3 is connected to the first the input of the adder 15. The outputs of the sensors 12 are connected to the inputs of the blocks 13, the outputs of which are connected to the inputs of the blocks 14, the outputs of the blocks 14 are connected to the inputs of the adder 5, the output of which is connected to the first input of the block 4, the second input of which is fed to the signal from the first output decoder 8, the output of block 4 is connected to the information input of the integrator 9, to the zero input of which the signal from the second output of the decoder B is fed, and to the memory input - the signal from the third output of the defroster. The integrator output is connected to the information input of the block 10, for clocks whose input is supplied with the signal from the third output of the decoder 8. The output of the block 10 is connected through filter 6 to the first input of the adder 5 to the second input of which is supplied: the signal from the first output of the decoder 8. The output of the adder is connected with the input of a controlled zary) of the generator 1.

The output of the generator 1 is connected to the distributor 2 of the control pulses of the inverter valves 16. The output of the synchronizer 11 of the control unit of the rectifier 17 is connected to the counting input

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ka 7, the output of which is connected to the input of the decoder 8.

The device works as follows.

When using sensor 3 in the constant current consumption circuit and the need to adjust the frequency converter to the maximum input current mode, which corresponds to the maximum output power of the frequency converter, the output signal of sensor 3 when the converter is operating on a resonant load is shown in the diagram (FIG. 2a) The diagram is shown without the ripple of the direct voltage supplying the autonomous inverter. When the inverter output voltage frequency changes and the load parameter changes, the parameters that are limited change. An example of a change in the signal at the output of sensor 12 is shown in the diagram (Fig. 2b). When the adjustment process limits the permissible level in the adjustment process, the signal at the output of block 13 appears. The signal from block 14 (Fig. 2d) is fed to adder 15, where it is subtracted from sensor 3 signal.

The signal from the output of the adder 15 (Fig. 2d) goes to block 4. From the diagram (Fig. 2d), it is obvious that at the time the restricted parameter reaches its permissible level, the signal at the input of block 4 reaches an extremum. Further regulation leads to a decrease in the signal at the input of block 4,

From the output of the synchronizer 11 of the control unit of the rectifier to the input of the counter 7 receives the clock pulses corresponding to the frequency of the pulsations of the constant voltage supplying the autonomous serial inverter 16, the Counter 7 counts the clock pulses, From the output of the counter 7 the signal goes to the drive} 1 trator 8.

At the same time, the same signal from the first output of the decoder 8 is fed simultaneously to the frequency control channel of the master oscillator 1 through the adder 5 and to the input of the block 4, providing, simultaneously with the frequency, changing the sign of the input information signal. The information signal generated in this way is fed to the input

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The integrator 9, which is transferred to the Memory mode by a signal from the third output of the Depth 8 generator. By this signal, unit 10 is transferred to the sampling mode. The signal from the second output of the decoder 8 in the integrator 9 resets the output signal and, thus, the inverter 9 is prepared for the next sequential integration operation — subtraction of the information signal. From the output of the integrator 9, the signal arrives at the input of the block 10, which, during the signal that arrives from the third output of the decipher of 15 attorney 8, samples the information, being in the storage mode for the rest of the time.

From the output of block 10, the resulting signal through the filter 6, 20 smooths the dynamic impulses of the sampling intervals, is fed to the second input of the adder 5 and causes the working point to move along the resonant characteristic of the load to the side 25 of the newly-formed extremum. The constant weight of block 14 determines the accuracy of the adjustment to the extremum .30

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The frequency converter with the proposed control method can operate as a stabilizer. For example, by choosing the output power of the converter as the limited parameter, it can be stabilized at any necessary level, which is required in some technological processes using induction heating.

The application of the proposed method allows to significantly increase the reliability of the converter 5 operation.

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Claims (1)

Stots and increase the resource time of trouble-free operation of the converter. Claims The method of controlling a frequency converter with a DC link, which consists in generating an alternating voltage of constant frequency synchronous with the frequency of the ripple of the input voltage of the inverter of the frequency converter, measuring the output power of the converter output parameter, for which they integrate the product of the output parameter and the alternating voltage at each period of the generated alternating voltage and memorize the values the integral at the end of the period, summarizes the memorized value of the integral with the frequency setting signal of the inverter and converts the resulting signal into the frequency of the inverter control pulses, characterized in that, in order to increase the reliability of the frequency converter, select the limited parameters, set the acceptable levels of the limited parameters, measured restricted parameters, determine the differences of the measured parameters and their permissible levels, fix the sign of the difference and form positive signals with positive differences constraints, for WHAT multiply the resulting differences by constant weights, the specified output parameter is the difference of the measured output power and the limit signals, and the weighting factors are chosen from the condition of obtaining a negative derivative of the output parameter from the moment the positive differences of the measured parameters appear and their acceptable levels .