JPS62163578A - Inverter - Google Patents

Abstract

PURPOSE:To reduce the disorder of an output waveform, by arranging the first and second signal generators for generating the output of each PWM signal independently, and by switching-controlling the generators with signal put together with each signal of it. CONSTITUTION:An inverter is provided with a commercial AC power source 1, a diode bridge 2, a smoothing condenser 3, and an inverter section 4, and the induction motor 6 of a load is driven by the inverter. The control circuit of the inverter is organized with a microcomputer 8 containing the first signal generator 10, a buffer 9, a base amplifier 7, and the second signal generator 11. Besides, from the both signal generators 10, 11, each PWM signal for output is independently generated, and each of the PWM signal is put together by the buffer 9. Then, on low output voltage, the output of the PWM signal with output voltage set to be high through the first signal generator 10 is generated, and is put together with signal from the second signal generator 11. As a result, even on low output generating frequency, a waveform is not disordered.

Description

[Detailed description of the invention] [Industrial application field] -77) 411tl I+l −/sword'/
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The present invention relates to an inverter device with an improved output voltage waveform, and particularly to an inverter device with an improved output voltage waveform.

[Conventional technology]

Figure 4 is a circuit configuration diagram showing this type of conventional pulse width modulation (PWM) control type inverter device, and is illustrated in the "Service Handbook Room Air Conditioner N" published by Mitsubishi Electric Corporation.
o, B-1504. In the figure, 1 is a commercial AC power supply, 2 is a diode bridge that rectifies the AC, 3 is a capacitor that smoothes the DC obtained by rectification, and 4 is an inverter unit that converts the DC into Sanwa AC. Power transistor 5 as an element
is used. 6 is an induction motor as a load, 7 is a base amplifier that drives the power transistor 5 of the inverter section 4, and each phase is
, (2) Output the respective switching signals to the power transistors 5 of η. 8 is a microcomputer (hereinafter referred to as microcomputer) having a PWM signal generator, and 9 is a microcomputer.

Next, the operation will be explained. AC power from a commercial AC power supply 1 is rectified by a diode bridge 2 to become DC power, and after being smoothed by a capacitor 3, it is input to an inverter unit 4.

On the other hand, the PWM signal output from the microcomputer 8 is input to the base amplifier 7 via the buffer 9, and from this base amplifier 7 to each power transistor 5 of the inverter section 4.
A switching signal is output. By driving each power transistor 5 in accordance with this switching signal, the direct current is switched, a pseudo three-phase alternating current is output from the inverter section 4, and the induction motor 6, which is a load, is driven.

FIG. 5 is a diagram showing a method of creating the PWM signal.

This type of PWM ffj control method generally compares the virtual output voltage of a carrier such as a triangular wave (A) and each phase (here, U phase (B) and V phase (C)) to determine the switching ON10. FF is performed, and the output wave number and voltage change depending on the carrier (A). Here, when the output voltage is low, the switching time is short, and pulses shorter than the shortest pulse time resulting from the processing time when controlling the operation by the microcomputer 8 are frequently required. Therefore, in actual operation, the shortest pulse is limited to 1lJl by the processing time of the microcomputer 8, etc., as shown by the broken line in FIG.
Disturbances occur in the output waveform. Furthermore, in the case of sine wave approximation PWM control, all output patterns must be changed when changing the output voltage.

It is necessary to have a pattern for each voltage.

[Problem that the invention seeks to solve]

Since the conventional inverter device is configured as described above, there is a problem that the output waveform is distorted when the frequency of the output voltage is low, and in order to change the output voltage, it is necessary to have many patterns for each voltage. There was a problem.

This invention was made with attention to such problems, and even when the output 'i mini is low, the waveform is not disturbed.
Another object of the present invention is to provide an inverter device that can easily obtain any output voltage.

[Means for solving problems]

The inverter device of the present invention includes a switching element controlled by a pulse width modulation signal, a first signal generator and a second signal generator each independently outputting the pulse width modulation signal.
A control means is provided for superimposing a modulation signal from the first signal generator and a modulation signal from the second signal generator to control switching of the switching element.

[Effect]

When the output voltage is low and the pressure is high, the first signal generator outputs a PWM signal with a high output voltage, and this signal and the second
A PWM signal from a signal generator is superimposed thereon, and the switching element is controlled by this signal so as to have a predetermined output. Since this two-step control is performed, the waveform is not disturbed even when the output voltage frequency is low, and the required output voltage can be easily obtained.

r　tiZ　jk　(to I) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit configuration diagram of an inverter device according to the present invention, in which 1 is a commercial AC power supply, 2 is a diode bridge, 3 is a smoothing capacitor, 4 is an inverter section using a power transistor 5 as a switching element, Reference numeral 6 indicates an induction motor as a load, and reference numeral 7 indicates a base amplifier, and these components are the same as those of the conventional one shown in FIG. 8 is a microcomputer incorporating a first signal generator 10, and 9 is a buffer, which is connected to a second signal generator 11 that outputs a PWM signal. The first and second signal generators Z+lO and 11 each independently output a PWM signal,
These PWM signals are superimposed in a buffer 9. The superimposed PWM signal is then used as a switching signal to control switching of the power transistor 5.

The control means for performing this switching control is composed of a buffer 9, and specifically, a signal generator 1 built into the microcomputer 8.
Sine wave PWM signal from 0 and PW from signal generator 11
The AND with the M signal becomes the output of the buffer γ9. Also, the second
The signal generator 11 is controlled by the microcomputer 8.

Next, the operation will be explained. As before, as shown in Fig. 2, the carrier (a) which is a modulated wave and the signal waves (b) and (c) of each phase are compared and the transistor 5 is turned 0N10FF, resulting in a predetermined output voltage of one frequency. Control as follows. Here, when the output voltage is low, PWM as shown in Figure 3
Output and control signals. That is, in order to prevent the pseudo sine wave output waveform from being disturbed, a high output is assumed in advance,
According to the output voltage, a sine wave approximation PWM signal is output from the first signal generator 10 built in the microcomputer 8 (the third
(See Figure 3(a)), or a PWM signal whose duty ratio (Ton/T) is set so that the output voltage from the second signal generator rji11 to the final stage becomes the initial target voltage (see Figure 3(b)). reference) is output. This duty ratio (Ton/
T ) is the virtual voltage (■1) above and the target voltage (Vz)
Then, these PWM signals are superimposed by the buffer 9 and output to the base amplifier 7 as a switching signal (see FIG. 3(C)). In this way, by setting a higher output voltage in advance,
Since it is controlled to return to its original state using a PWM signal from a separately provided signal generator 11, it is possible to reduce the number of cases where the shortest pulse time is restricted compared to the conventional method, and the disturbance in the output waveform is small. becomes.

Also, by changing the duty ratio of the PWM signal from the second signal generator 11, the sine wave PW from the microcomputer 8 can be changed.
For example, if the output signal of the signal generator 11 of m2 is a constant value signal as shown in FIG. 3(d), the signal input to the base amplifier 7 is The signal generated is the same as the output signal of the signal generator 10 of tjSl shown in FIG. 3(a), and the virtual output voltage in FIG. 2 is obtained as the actual output voltage.

In this way, since two independent PWM signal generation sources are provided and the signal is processed in two stages, waveform disturbances at low output voltages are suppressed, and any output voltage can be easily obtained. It will be a round trip.

〔Effect of the invention〕

As explained above, according to the present invention, the first . a second signal generator;
Since the switching is controlled by a signal obtained by superimposing these PWM signals, the disturbance in the output waveform is reduced even when the output voltage is low, and it is possible to easily convert any output voltage.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing one embodiment of the present invention,
Figure 1 is a circuit configuration diagram, Figure 2 is an explanatory diagram showing how to create a PWM signal, Figure 3 (a), (b), (c)
. (d) is a diagram showing the output waveform of the signal generator, Figure 4 is a circuit diagram of a conventional inverter device, and Figure 5 is a diagram of a conventional PWM device.
A description showing a method of creating a signal [Fig. J1]. 4...Inverter section 8...Microcomputer 9...
...Buffer (control means) 10...First
Signal generator 11...Second signal generator Note that the same reference numerals in the drawings indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In an inverter device that controls switching elements with a pulse width modulation signal and converts direct current into arbitrary pseudo alternating current, first and second signal generators each independently outputting the pulse width modulation signal are provided. , an inverter device comprising a control means for superimposing a modulation signal from the first signal generator and a modulation signal from the second signal generator to control switching of the switching element. (2) The inverter device according to claim 1, wherein the control means changes the inverter output voltage by changing the duty ratio of the modulation signal from the second signal generator.