SU1615851A1 - Method of converter voltage inverter - Google Patents

Abstract

The invention relates to electrical engineering and can be used in an AC electric drive with frequency-current control. The purpose of the method is to improve the accuracy of tracking the shape of the load current of the inverter. In the method, the switching of the inverter valves is controlled. To do this, they form a signal for setting the load current, compare it with the actual instantaneous value of the inverter load current, determine the sign of the error signal at the time of arrival of the clock pulse, simultaneously remember the sign of the error signal, compare it with the sign that has the error signal at the moment of arrival of the previous clock pulse. If the signs are unequal, the switching signals of the inverter valves are generated. In this case, the inverter output current is always controlled with an alternating error, and the period of the following clock pulses changes as a function of the instantaneous value of the signal for the load current of the inverter. 2 Il.

Description

The invention relates to electrical engineering and can be used in voltage inverters designed for a variable frequency drive.

The purpose of the invention is to improve the accuracy of tracking the shape of the inverter load current.

Fig. 1 shows a functional diagram of a device implementing the proposed method for controlling a voltage inverter; 2 are diagrams of control signals of this device.

The device contains a source of 1 reference signals, a voltage-frequency converter 2, a first driver 3 harmonic signals controlled in frequency and amplitude, a second driver

4 harmonic signals, controlled by frequency and amplitude, comparator 5, node b of the separation of the signal of the load current, block 7 of two D-flip-flops, a bridge-type inverter on four keys 8-11 with a load 12, a summing device 13, a generator of 14 clock pulses , source 15 constant voltage.

The first output of source 1 of reference signals through converter 2 is voltage-frequency connected to the first inputs of drivers 3 and 4 harmonic signals, the second inputs of which are connected to the second output of source 1 of reference signals connected to the second input of summing device 13, the third input of which is connected to output source 15

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The first input is connected to the output of the second shaper 4 of the harmonic signal. The output of the first shaper 3 of the harmonic signal is connected to the first input of the comparator 5, the second input of which is connected to the node 6 for extracting the load current signal. The comparator output Ef is connected to the information inputs of Block 1 of two D-flip-flops, the E1 IN gating of which is connected to the generator output of 14 clock pulses, the input of the latter is connected to the output of summing device 13. The outputs of the 7-D-flip-flop unit are connected to control inputs of $ -11 keys inverter.

The method is carried out as follows: | {) az.

; The signal of the frequency setting f is applied to the digital inputs of the first 3 and second 4 form- ||) harmonic signals (Fig. 1), and the second inputs of which are fed a lie signal setting the current amplitude 1t. At the output of the First block 3, a harmonic signal is set for setting the load current, up- (equivalent in frequency and amplitude (Fig. 2). At the output of the second block 4, signal Nal 18 is formed, shifted by a quarter of the period relative to the signal of the current, whose frequency synchronous changes with double frequency, the amplitude is proportional to: the voltage amplitude setting voltage ignition 16. In the eloke 13, the signal 18 from the output of 5 block 4, the signal 16 from the second output of unit II and the level-controlled signal 19 from the output of the source 15 are summed. | this device 13 form Signal 20 controls the period of the clock pulses of the generator 14. As a result, clock pulses are generated at the output of the generator 14, the tracking period of which changes simultaneously with the change in the instantaneous value of the current command signal 20.

The signal 17 for setting the current Us at the output of block 3, which determines the shape of the current in the load 12 of the inverter, is applied to one of the inputs of the comparator 5, to the other input of which a signal 21 is supplied proportional to the load current UH. In comparator 5, the signals Uz and UH are compared. If UH Ua, the output of the comparator 5 is signal 1, if the UH is the Us signal O. The signal from the output of comparator 5 is fed to the information inputs of two D-flip-flops. The change in the state of D-flip-flops occurs at the moments when the D-flip-flops of clock pulses generated by the 14-clock pulse generator arrive at the gate input.

If the signal at the output of comparator 1, then at the moment when the clock pulse arrives at the gate input of the D-flip-flops, signals G appear on their direct outputs Va, V4, and on the inverse outputs Vi, Va - O. the control inputs of the power switches 8-11 of the inverter and switch them to a state in which the keys 9 and 11 are closed, and the keys 8 and 10 are open, and a negative polarity pulse is applied to the unloading. Under the action of this pulse, the load current 21 decreases, which leads to a change in the error signal.

If the sign of the error signal has changed

UH Us, then the output of the comparator 5 will be a signal O, and at the moment of arrival of the clock pulse to the gate input of D-flip-flops on the direct outputs V2, V4 of D-flip-flops there appears a signal O, and on the inverse outputs - 1. These signals come to the control inputs of the power switches and switch them to the state in which the keys 9 and 11 are open and the keys 8 and 10 are closed. In this case, a voltage pulse of positive polarity is applied to the load 12, under the action of which the load current 21 begins to increase, which leads to a change in the sign of the error signal. With UH Us, the output of comparator 5 will be signal 1. Further, the processes are repeated.

Thus, according to the proposed method, signals are generated at the output of the clock generator, the period of which changes simultaneously with the change in the instantaneous value of the reference signal. The greater the instantaneous value of the target signal, the longer the period of the clock pulses. The minimum and maximum values of the period of the clock pulses are set depending on the type, nature and range of the load change.

Formation of the output current of the inverter with the use of clock pulses with a variable period of following allows to increase the accuracy of the formation of the load current.

Claims (1)

Invention Formula The method of controlling the voltage inverter, which consists in generating a current setting signal and a signal proportional to the instantaneous values of the load current, generates an error signal by comparing the current setting signal and a signal proportional to the instantaneous values of the load current, determine the sign of the error signal , form clock pulses, remember the sign of the error signal in moments forming clock pulses, comparing it with the error signal sign at the moment of forming the previous clock pulse, when changing the sign of the error signal, they generate switching signals for the inverter valves, characterized in that, in order to improve the accuracy of tracking the output current form of the inverter load, they are shifted by a quarter of the period regarding 0 The current setting signal is a harmonic waveform, the amplitude of which is proportional to the amplitude of the current setting signal, and the frequency is equal to twice the frequency of the current setting signal, is summed with the amplitude value of the current setting signal and a constant value signal, which is proportional to the instantaneous value of the resulting sum signal. about / Fig.G W t / t 17