JPH0336965A - Pwm inverter - Google Patents

Abstract

PURPOSE:To improve an output voltage waveform by causing the peak of a triangular wave to have a raising period of constant width and constant height and by level-comparing the triangular wave with a sine wave. CONSTITUTION:A PWM inverter compares the carrier wave of a triangular wave with a sine wave to form a PWM waveform and the switching element of an inverter main circuit is ON.OFF controlled by the use of the PWM waveform as a gate signal. Further, a counter 1, ROMs 2, 3, D/A converters 4, 5, a voltage-controlled amplifier 6, a multiplier 7, a comparator 8 and a gate circuit 9 are used for the ON.OFF control to obtain a gate output. In this case, triangular wave data to be written in the ROM 3 are used as sample data formed by superimposing a pulse on a peak part and the peak is caused to have a raising period of constant width and constant height.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a PWM inverter, and particularly to a PWM waveform generation circuit.

B3 Summary of the Invention The present invention provides a PWM inverter that obtains a PWM wave by comparing the levels of a triangular wave and a 712 chord wave, in which the 31. By providing a second period, the correlation between the sine wave and the PWM wave at a control rate of 1 or more is increased.

C3 Conventional technology A PWM inverter generally generates a PWM waveform by comparing a triangular carrier wave and a sine wave, and uses this PWM waveform as a gate signal and 17 to turn on/off switch elements in the inverter main circuit 11-1PW Obtain waveform inverter output. At this time, the inverter output frequency becomes the frequency of the sine wave, and the output voltage is controlled by the amplitude of the sine wave.

Problem to be solved by the D2 invention In the conventional PWM type inverter, the control rate is the state where the peak of the sine wave and the peak of the triangular wave match! Therefore, it is generally operated within a control ratio range of 1 or less, where the peak of the sine wave is lower than that of the triangular wave.

However, during control of the inverter load, the control rate temporarily changed to 1.
As mentioned above, it may be convenient to increase the output voltage, and in this case, control is performed such that the amplitude of the sine wave is set to a triangular wave or lower. In this case, the PWM waveform will have a portion where the sine wave and triangular wave do not intersect.

Figure 3 shows sine waves, triangular waves, and PWM when the control rate is less than 1.
Each waveform diagram of the wave is shown, and FIG. 4 shows each waveform diagram when the control rate is 1 or more. As is clear from both figures, during the period when the control rate is 1 or more, the pulse width ratio of the PWM waveform does not correspond to the amplitude change of the sine wave, and the inverter output voltage increases, but the distortion in the output voltage waveform increases. The advantages of the PWM method will be lost, and the sudden increase in inverter peak current may damage the load.

An object of the present invention is to provide a PWM inverter that improves the correlation between a PWM waveform and a sine wave at a control rate of 1 or more.

E, the -p stage and action for solving the problem The present invention is h
In order to achieve this goal, the flaw angle is The wave is equipped with a waveform generating means that has a constant width and a constant amplitude raising period at the peak point, and when the sine wave has a control rate of 1 or more, it is switched on and off near the peak of the sine wave in comparison with the triangular wave. Hold the part 1) W
Obtain M waveform.

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

The counter 1 receives a clock signal CK proportional to the inverter output frequency as a counting input, and uses the counted value as an addresser of the ROM 2.3. The ROM 2 has sample data of the amplitude of the sine wave written therein, and sequentially outputs the sine wave amplitude data according to the count value of the counter l. ROM 3 contains sample data of the amplitude of the triangular wave! 'I) entered, counter 1
The triangular wave amplitude data is sequentially output according to the count value. The output data of these ROMs 2.3 are sent to D/A converters 4.
5, the sine wave analog signal (constant amplitude) is taken out to the D/A converter 4, and the D/A converter 4 receives the analog signal (constant amplitude).
A triangular wave analog signal (constant amplitude) is taken out to the A converter 5.

The voltage control amplifier 6 compares the inverter output voltage setting signal Vs and the impark output voltage detection signal f to obtain a voltage control signal. The multiplier 7 uses the voltage control signal from the amplifier 6 as a multiplier, uses the sine wave signal from the D/A converter 4 as a multiplicand, and amplifies the amplitude of the sine wave signal in accordance with the voltage control signal. The comparator 8 obtains a PWM waveform by comparing the levels of the sine wave output of the multiplier 7 and the triangular wave output of the D/A converter 45. The gate circuit 9 receives I)WM from the comparator 8.
A gate output is obtained that drives the switch elements of the inverter main circuit according to the waveform.

Here, the triangular wave data written to the ROM 3 is made into sample data in which a pulse is superimposed on the peak portion. As shown in FIG. 2, the triangular wave based on the sample data in the ROM 3 has a rising period of constant width and constant crystallinity at the peak point, as shown in FIG.

In contrast to the above-mentioned triangular wave, when the control rate is less than 1, a PWM wave whose width is below the peak level Pr and which corresponds to the sine wave amplitude is obtained, as shown by the broken line in FIG. 2, as in the prior art. Then, the sine wave exceeding the control rate l (solid line in Figure 2) is separated by the pulse width of the raising period ['WM
Become a wave. That is, even when the control rate is set to 1 or more, the correlation between the amplitude of the sine wave and the PWM wave is reduced, the distortion rate increase of the inverter output voltage waveform is suppressed, and the PWM waveform suppresses a sudden increase in the inverter peak current. can be obtained.

Effects of the G1 Invention As described above, according to the present invention, the peak point of the triangular wave has a bulk period of a constant width and constant height to compare the level with the sine wave. The PWM pulse width ratio is well matched to the sine wave that is set to −,
By increasing the correlation between the sine wave and the PWM wave, it is possible to improve the inverter output voltage waveform and suppress a rapid increase in the inverter peak current.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of the embodiment, FIG. 3 is a waveform diagram for a control rate of 1, and FIG. 4 is a conventional waveform for a control rate of l. It is a diagram. l...Counter, 2, 3...ROM, 4.5...
D/A converter, 6... Voltage control amplifier, 7... Multiplier,... Comparator, 9... Gate circuit. Fig. 1 Circuit diagram of the embodiment f 9-11 gate circuit Fig. 2 Waveform diagrams of the embodiment Fig. 3 Waveform diagrams of the control rate 1 Fig. 4 Waveform diagrams of the control rate 1

Claims (1)

[Claims] (1) A sine wave with an amplitude according to the output voltage control signal,
In a PWM inverter that obtains a PWM wave for controlling the main circuit switch by comparing the level with a triangular wave of constant amplitude,
PWM characterized in that the triangular wave is provided with a waveform generating means having a rising period of constant width and constant amplitude at the peak point.
method inverter.