JPH074066B2 - Control circuit for 3-phase inverter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control circuit for a three-phase inverter in which output voltage waveform distortion is small even when a load having a high high-frequency content or a single-phase load is connected.

[Conventional technology]

Electronic devices such as computers generally use a constant-voltage constant-frequency power supply device (hereinafter abbreviated as CVCF power supply device) because the allowable fluctuation range of voltage and frequency required for the power supply is small. However, this CVCF power supply device has a rectifier that converts commercial AC power to DC power,
The DC power output by this rectifier is a constant voltage / constant frequency 3
It is composed of an inverter that converts phase AC power, and is equipped with a battery so that it can be backed up by this battery so that the power supply to the computer can be continued even when the commercial AC power fails if necessary.

By the way, the computer, which is the load of the CVCF power supply,
In most cases, the input circuit of the internal power supply is a capacitor input type rectifier circuit. Therefore, the normal
In the CVCF power supply device, the output voltage waveform is distorted, and the computer malfunctions.

For this, for example, bipolar transistors or MO
Three single-phase inverters that use semiconductor switching elements that can perform high-speed switching such as SFET (metal oxide semiconductor field effect transistor) are combined to form a three-phase inverter. It is solved by proper control.

FIG. 2 is a main circuit connection diagram showing a conventional example of a three-phase inverter that supplies three-phase AC power to a load having a high harmonic content.

In FIG. 2, reference numerals 11, 12 and 13 are smoothing capacitors, and reference numerals 14, 15 and 16 are single-phase inverters as a single-phase power converting means, and the DC power from the DC power supply 2 is fed to a smoothing capacitor. It is converted into single-phase AC power separately with the phase inverter. So three single-phase inverters
Three-phase AC power is supplied to the computer 3 as a load by combining the outputs of 14, 15 and 16 with a phase difference of 120 degrees from each other. These three single-phase inverters
Inverter control circuits 17, 18,
A bipolar transistor, which is provided with 19 and constitutes a semiconductor switching element of the inverter, is subjected to high-speed switching operation by appropriate control to supply AC power with a small waveform distortion to the computer 3.

FIG. 3 is a control block diagram showing a conventional example of the inverter control circuit shown in FIG.

The operation of the control circuit shown in FIG. 3 is as follows. That is, a transformer for a single-phase instrument (hereinafter abbreviated as single-phase PT)
For example, 20 detects the output voltage of the first-phase single-phase inverter 14 and converts it into a smooth detection voltage signal by the rectifier circuit 21 and the filter circuit 22. On the other hand, since the voltage setting device 23 sets the voltage that this single-phase inverter 14 should output,
Proportional-integral adjustment circuit (abbreviated as PI adjustment circuit below) 24
The deviation between the detected voltage signal and the set voltage signal is input to and the signal for controlling the input deviation to zero is taken out from the PI adjusting circuit 24.

Reference numeral 28 is an oscillator circuit for outputting a clock pulse,
The memory 26 containing the sine wave data, the counter 27 and the clock pulse generate a digital sine wave signal, and apply this to the multiplying D / A converter 25. PI adjustment circuit 2
The analog sine wave signal with the amplitude corresponding to the output signal of 4 is output.

The proportional adjusting circuit (hereinafter abbreviated as P adjusting circuit) 29 inputs the deviation between the sine wave signal output by the multiplying D / A converter 25 and the detected voltage signal of the sine wave signal detected by the single-phase PT20. Amplify this.

Since the carrier wave generation circuit 31 outputs, for example, a triangular wave-shaped carrier wave having a high frequency based on the clock pulse from the oscillator circuit 28, the pulse width modulation circuit ( In the following, abbreviated as PWM circuit) 30, pulse width modulation is performed, and an ignition signal is sent to each bipolar transistor constituting the single-phase inverter 14 via an ignition signal circuit 32, and these are sequentially turned on / off. Single-phase alternating current is output from this inverter 14.

Since the other single-phase inverters 15 and 16 are also provided with the inverter control circuits 18 and 19 having the configurations shown in FIG. 3, respectively, the single-phase AC output by the three single-phase inverters 14, 15 and 16 is output. By shifting the phase of each other by 120 degrees in terms of electrical angle, 3
You can get mutual exchange.

[Problems to be Solved by the Invention]

As described in FIG. 2 and FIG. 3, a capacitor input type rectifier circuit such as a computer is formed by three single-phase inverters 14, 15, 16 and three sets of inverter control circuits 17, 18, 19. Even if it is a load, it is possible to supply three-phase AC power with less waveform distortion, but even if it is unavoidable to use two single-phase inverters, three inverter control circuits are also used, so parts There are disadvantages that the number of points is large, the apparatus becomes large, and the cost also rises.

Therefore, an object of the present invention is to reduce the number of parts of the control circuit of the three-phase inverter by sharing the control circuit of the three-phase inverter that combines three single-phase inverters to obtain three-phase AC power. It is to reduce the size and cost.

[Means for Solving the Problems]

In order to achieve the above object, the control circuit of the present invention is
In a three-phase inverter formed by combining three single-phase power conversion means configured by bridge connection of semiconductor switching elements, a rectification means for outputting an average value of three-phase AC voltage output by the three-phase inverter And a proportional-plus-integral adjusting means for adjusting the deviation between this average value and a voltage separately set to zero, and three sets of sine-wave signals with amplitudes corresponding to the output signals of the proportional-plus-integral adjusting means for each phase. Sine wave generating means, three sets of proportional adjusting means for adjusting the deviation between the sine wave signal and the output phase voltage of the three-phase inverter for each phase, and the output signal of the proportional adjusting means for each phase is pulsed with a carrier wave. There are provided three sets of pulse width modulation means for performing width modulation, and three sets of firing signal generation means for producing firing signals to be separately given to the three single-phase power conversion means from the output signals of the pulse width modulation means. To assume

[Action]

The present invention can reduce the output impedance of this inverter in an inverter that performs high frequency modulation using a high-speed semiconductor switch element. However, if the output impedance is reduced, an unbalanced load (for example, a single-phase load) can be added to a three-phase AC output. ) Is applied, the three-phase output voltage hardly changes. Therefore, proportional-integral control is performed by the average value of the three-phase AC line voltage to make the output voltage constant. Furthermore, by proportionally controlling each phase voltage, distortion of the output voltage waveform can be suppressed even when a capacitor input type rectifier circuit is a load.Therefore, only proportional control of each phase voltage is required for such control. Although it is performed for each single-phase inverter, the proportional-integral control with the three-phase AC line voltage average value is performed collectively for three phases.
The number of parts is reduced.

〔Example〕

FIG. 1 is a control block diagram showing an embodiment of the present invention, which is a circuit for controlling all three single-phase inverters.

In FIG. 1, the three-phase AC voltage obtained by combining three single-phase inverters is detected by the three-phase PT40, and the rectifier circuit 41 and the filter circuit 42 obtain a smooth detected voltage signal. Then, the PI adjusting circuit 24 is caused to perform the operation of controlling the deviation between the detected voltage signal and the set voltage signal by the voltage setter 23 to be the same as in the case of the conventional example circuit described above in FIG. is there. And these three-phase PT40, rectifier circuit 41,
Filter circuit 42, voltage setting device 23 and PI adjustment circuit 24
Need only be prepared for each of the three single-phase inverters. Oscillator circuit 2 that outputs clock pulses
Similarly, the counter 27, the carrier 27, and the carrier wave generation circuit 31 may be prepared for each of the three single-phase inverters.

The first-phase inverter of the three single-phase inverters is a multiplication type D / A converter 25A, a memory 26A, and a P adjustment circuit 29.
A, a PWM circuit 30A, and an ignition signal circuit 32A are prepared, and the same operation as the conventional example circuit described in FIG. 3 is performed. That is, by multiplying the digital sine wave signal obtained by the oscillation circuit 28, the counter 27 and the memory 26A, and the output signal of the PI adjustment circuit 24 in the multiplication type D / A converter 25A,
An analog sine wave signal is obtained. This analog sine wave signal has a large amplitude when the output of the PI adjustment circuit 24 is high, and a small amplitude when the output of the PI adjustment circuit 24 is low.

The analog sine wave signal obtained in this way and the three-phase PT40
The deviation from the first phase voltage signal extracted from the P adjustment circuit 29A
The pulse width modulation is performed by the PWM circuit 30A with the carrier wave output from the carrier wave generation circuit 31. The result is given to the first phase inverter via the ignition signal circuit 32A.

Multiplying D / A converters 25B and 25 provided for the second phase inverter and the third phase inverter, respectively
C, memories 26B and 26C, P control circuits 29B and 29C, PWM circuit 30
B and 30C and the firing signal circuits 32B and 32C perform the same operation as above.

〔The invention's effect〕

According to the present invention, three single-phase inverters configured by semiconductor switching elements that perform high-speed switching operation are combined to form a three-phase inverter. The three-phase line voltage output from the three-phase inverter is By detecting the average value and performing proportional-integral control on the average value, the output voltage is controlled to a constant voltage, while the phase voltage is proportionally controlled for each phase. In this case, the proportional control portion of each phase voltage requires a control circuit for each of the three single-phase inverters, but one control circuit other than this may be prepared commonly for the three single-phase inverters. Therefore, even when an unbalanced load or a load having a high high-frequency content is connected, the effect of being able to control the three-phase AC power without waveform distortion with a low-cost control circuit having a small number of parts is obtained.

[Brief description of drawings]

FIG. 1 is a control block diagram showing an embodiment of the present invention,
FIG. 2 is a main circuit connection diagram showing a conventional example of a three-phase inverter that supplies three-phase AC power to a load having a high harmonic content, and FIG. 3 shows a conventional example of the inverter control circuit shown in FIG. It is a control block diagram. 2 ... DC power supply, 3 ... Computer as load, 1
1,12,13 …… Smoothing capacitor, 14,15,16 …… Single-phase inverter, 17,18,19 …… Inverter control circuit, 20 …… Single-phase P
T, 21,41 …… Rectifier circuit, 22,42 …… Filter circuit, 23…
… Voltage setter, 24 …… PI adjustment circuit, 25,25A, 25B, 25C ……
Multiplying D / A converter, 26,26A, 26B, 26C ... Memory, 2
7 …… Counter, 28 …… Oscillation circuit, 29,29A, 29B, 29C ……
P adjustment circuit, 30, 30A, 30B, 30C ... PWM circuit, 31 ... Carrier wave generation circuit, 32, 32A, 32B, 32C ... Ignition signal circuit.

Claims (1)

[Claims] 1. In a three-phase inverter formed by combining three single-phase power conversion means configured by bridge connection of semiconductor switching elements, an average value of three-phase AC voltage output by the three-phase inverter. Rectifying means for outputting, a proportional-plus-integral adjusting means for adjusting the deviation between the average value and a voltage separately set to zero, and a sine-wave signal with an amplitude corresponding to the output signal for the proportional-plus-integral adjusting means for each phase. Three sets of sine wave generating means for outputting, three sets of proportional adjusting means for adjusting the deviation between the sine wave signal and the output phase voltage of the three-phase inverter for each phase, and output signals of the proportional adjusting means for each phase 3 sets of pulse width modulation means for performing pulse width modulation with a carrier wave for each of them, and 3 sets of firing signals for creating firing signals to be separately given to the three single-phase power conversion means from the output signals of the pulse width modulation means With generating means Control circuit of three-phase inverter, characterized in that there.