JPH01170375A - Control circuit for inverter - Google Patents

Abstract

PURPOSE:To correct a waveform distortion by comparing the detected value of the output voltage of an AC filter with a reference sine wave output voltage, and adding a correction to a PWM circuit. CONSTITUTION:An inverter 1 converts a DC input 1 to a variable-voltage, variable-frequency power and supplied it through an AC filter 3 to a load 6. There are also provided a PWM circuit 4, a pulse distribution amplifier 5, and a filter 9 connected through a transformer 17 and a rectifier 8 to a connecting point 7. The output of the filter 9 and a voltage setter 11 are connected to a comparator 10, and the output of a reference sine wave generator 13 is input through a comparator 12 and an element inverter 18 to the PWM circuit 4. Thus, when the detected value of the output voltage of the filter 9 is compared with the reference sine wave output voltage, the output of the comparator 10 becomes a correction signal, and outputs an output signal corrected by the PWM circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter control circuit that corrects a PWM output waveform in order to reduce distortion of an AC voltage applied to a load in the case of a rectified load.

[Conventional technology]

Conventionally, the rectangular wave PWM method and the sine wave PWM method are typical as control methods for inverters. Sine wave PW
In the M method, it is possible to obtain a sine wave with less harmonic content using a small filter, but because the voltage utilization rate is poor, it is necessary to increase the input DC voltage or install a step-up transformer on the output side, and the main circuit current also increases. There is a problem.

On the other hand, the rectangular wave PWM method is easy to control and has a good voltage utilization rate.

[Problem that the invention seeks to solve]

However, in order to obtain a sine wave output, a large AC filter is required, and in the case of a rectifying load such as a rectifier, the output voltage of the AC filter installed on the output side of the inverter is the output voltage of the rectifying load shown in Figure 2. As shown by the voltage detection value C, there is a problem that the waveform becomes flat near the maximum value and a third harmonic component is generated.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inverter control circuit that does not require an AC filter to obtain a sine wave output and reduces distortion with respect to a rectified load.

[Means for solving problems]

In order to achieve the above object, the inverter control circuit of the present invention includes a PWM circuit that outputs a PWM signal according to a setting value of a frequency setter, and an inverter that converts a DC power supply voltage into an AC of variable voltage and variable frequency. a reference sine wave oscillator that generates a sine wave voltage synchronized with the output voltage of the inverter; and detection of an output voltage supplied to the load of the inverter. A comparator is provided which compares the output voltage of the sine wave oscillator with the output voltage of the sine wave oscillator and supplies the output thereof to the PWM circuit.

[Effect]

According to this invention, when the reference sine wave output voltage is compared with the detected value of the output voltage of the AC filter, the output of the comparator outputs a correction signal, and when this signal is given to the PWM circuit, the PWM circuit makes the correction. The output signal will be output.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the invention.

In the figure, 1 is an inverter that converts a DC power supply voltage into a variable voltage and variable frequency voltage, and 3 is an AC filter. 4 is a PWM circuit, which includes a triangular wave oscillator for generating a modulation signal, a sine wave oscillator that generates a sine wave voltage of constant amplitude at a frequency corresponding to a set voltage of a frequency setting device (not shown), and a sine wave oscillator that generates a voltage of this sine waveform and a triangular wave. It is equipped with a comparator that compares the triangular wave voltage of the oscillator and outputs a signal for driving the switching element of the inverter. Reference numeral 5 denotes a pulse distribution amplifier that sequentially distributes and amplifies the pulses generated in the PWM circuit 4 to a plurality of switching elements constituting the inverter 1. 6 is a load, and a filter 9 is connected to a connection point 7 via a transformer 17 and a rectifier 8. This filter 9 smoothes the DC input and obtains a constant voltage DC. The output side of this filter 9 is a comparator 10
A voltage setting device 11 is connected to the coining input terminal. Further, the negative input terminal of another comparator 12 is connected to the output side of the transformer 17, and the output of a synchronous circuit (not shown) is input to the coining input terminal to generate a reference sine wave that outputs a sine wave of a synchronized frequency. device 13 is connected. In addition, an element inverter 1 for output inversion is connected to the output side of the comparator 12.
8 are connected.

In this configuration, when the DC power supply 2 is connected to the inverter 1, the inverter 1 is turned on by the signal from the PWM circuit 4, and the inverter output voltage a shown in FIG.
A rectangular wave is output as shown in FIG. 2, and the AC filter 3 outputs an AC voltage with a continuous waveform as shown in the detected value of the output voltage of the AC filter 3 in FIG. The output voltage indicated by the detected value is of variable frequency and variable voltage by the inverter I. Further, the DC voltage formed via the transformer 17, the rectifier 8 and the filter 9 is compared with the set voltage of the setting device 11 in a comparator 10, and when the set voltage is higher than this DC voltage, the output voltage of the comparator 10 is , the voltage becomes large, and when the set voltage is smaller than the detection voltage, the voltage becomes small.

On the other hand, the detected value of the output voltage of the AC filter 3 is also input to the negative input terminal of the comparator 12 via the transformer 17, and the sine wave output voltage e of the reference sine wave generator 13 is input to the coining input terminal.
is input and this sine wave output voltage e is larger than the detected value of the output voltage of the AC filter 3, the comparator 12
The output voltage of the element inverter 18 becomes a large voltage, and conversely, when it is small, the output voltage of the element inverter 18 becomes a small voltage.

If the load 6 is a rectifying load, the comparator 12 outputs a large voltage in a range A where the detected value C of the output voltage of the AC filter 3 obtained through the transformer 17 is smaller than the sine wave voltage e. Then, it is superimposed on the output signal g of the sine wave oscillator in the PWM circuit 4 as a correction signal. Based on this correction signal, the sine wave oscillator output signal g rises in the correction signal output section A and is corrected to a sine wave signal ga as shown in FIG. By comparison with the carrier wave f, the pulse width is expanded from the waveform shown by the thin line to the waveform shown by the solid line.

As a result, the output voltage C of the AC filter 3 becomes a sine wave as shown in FIG. 2, and the same sine wave as in the case of a linear load is obtained.

〔Effect of the invention〕

According to this invention, the reference sine wave output voltage and the detected value of the output voltage of the AC filter are compared, and the PWM circuit is corrected based on the output of the comparator, so that the output of the PWM circuit is adjusted when the rectifier is loaded. Therefore, the distortion of the inverter output voltage waveform can be corrected without using a filter for the third harmonic of the inverter output voltage waveform.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the invention, and FIGS. 2 and 3 are voltage and current waveform diagrams of various parts for explaining the invention in detail. DESCRIPTION OF SYMBOLS 1... Inverter, 4... PWM circuit, 5... Distribution amplifier, 12... Comparator, 13... Reference sine wave generator.

Claims (1)

[Claims] 1) An inverter equipped with a PWM circuit that outputs a PWM signal according to the setting value of a frequency setter, and a distribution amplifier that distributes the PWM signal to an inverter that converts a DC power supply voltage into an AC with variable voltage and variable frequency. In the control circuit, a reference sine wave generator generates a sine wave voltage synchronized with the output voltage of the inverter, and a detected value of the output voltage supplied to the load of the inverter is compared with the output voltage of the reference sine wave generator. and a comparator for supplying the output to the PWM circuit.