JPH04236171A - Method for suppressing output voltage waveform distortion of inverter - Google Patents

Abstract

PURPOSE:To remove a distortion of a waveform near a zero-cross of an output voltage of a conventional inverter. CONSTITUTION:A method for suppressing an output voltage waveform distortion of an inverter for comparing a sine wave with a triangular wave increased in frequency to control a switching element of the inverter through an arm short-circuit preventing circuit, comprising the steps of forming the triangular wave to a variable frequency triangular wave (b) in which its frequency is reduced near phases 0 deg., 180 deg. of a comparing sine wave (a) and increased near phases 90 deg., 270 deg., and increasing the width of an ON pulse near phases 0 deg., 180 deg., thereby preventing vanishment of the ON pulse near the phases 0 deg., 180 deg. by the arm short-circuit preventing circuit.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for suppressing inverter output voltage waveform distortion.

0002

2. Description of the Related Art FIG. 2 shows the configuration of an inverter or a general-purpose inverter used in an uninterruptible power supply (UPS).

In FIG. 2, 1 is a DC power supply, 2 is an inverter consisting of switching elements SW1 to SW4 connected to the DC power supply 1, and 3 is connected to the inverter 2 via a filter circuit consisting of a reactor L1 and a capacitor C1. It's a load.

It is desirable that the waveform of the output voltage Vout of the inverter 2 is a sine wave like the commercial power supply. Therefore, as shown in FIG. 5, a method of generating on/off signals applied to the gates of the switching elements SW1 to SW4 by comparing a sine wave a and a triangular wave C having a constant frequency is currently often used.

Currently, in order to suppress the noise generated by the inverter, there is a tendency to increase the switching frequency of the inverter, that is, the frequency of the triangular wave C in the conventional method.

On the other hand, the on/off signal generation circuit is equipped with an arm short-circuit prevention circuit in order to prevent a period in which the upper and lower switching elements of the same arm of the inverter are turned on simultaneously, that is, to prevent an arm short-circuit of the inverter. ing. The arm short-circuit prevention circuit is configured as shown in Fig. 6, in which a rectangular wave on-pulse V1 is converted into a sawtooth voltage V2 by a charging/discharging circuit consisting of a resistor R1, a capacitor C2, and a diode D1, and the voltage V2 is set to a predetermined level. When the level is reached, the hysteresis comparators CP1 and CP
2, a rectangular wave-like on-pulse V3 with a narrowed width of the on-pulse V1 is output (see FIG. 7).

[0007]

According to the above-mentioned conventional on-off signal creation method, the on-pulse V1 created near the phase 0° or 180° of the comparison sine wave a is short due to the above-mentioned increase in the switching frequency. Become. Therefore, in the latter stage of the arm short-circuit prevention circuit, as shown in FIG.
disappears, and due to this, the inverter output voltage Vou
There was a problem that the waveform of t was distorted near the zero cross (0°, 180°).

The present invention has been made in view of the above-mentioned problems of the conventional technology, and its purpose is to suppress distortion near the zero cross of the inverter output voltage and maintain low noise. An object of the present invention is to provide a method for suppressing output voltage distortion of an inverter.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the inverter output voltage waveform distortion suppression method according to the present invention involves arm short-circuiting the output of an on-off signal generation circuit that compares a sine wave and a high-frequency triangular wave. In an inverter that outputs the signal through a prevention circuit to control the switching elements of the inverter, the triangular wave is compared.The frequency is low near the sine wave phase of 0° and 180°, and the frequency is low near the sine wave phase of 0° and 180°, and
A variable frequency triangular wave whose frequency increases near 70° is used to suppress distortion near the zero cross of the inverter output voltage.

0010

[Operation] The frequency of the triangular wave is the phase of the comparison sine wave 0°, 18
When it becomes low near 0°, the on-pulse width near 0° and 180° output from the on-off signal generation circuit becomes longer than when the frequency of the triangular wave is constant, so even if the frequency of the triangular wave is passed through the arm short circuit prevention circuit, It does not disappear as it does in certain cases. Therefore, it is possible to suppress distortion near zero crossing of the inverter output voltage waveform that occurs when the frequency of the triangular wave is constant. Also, 90°, 27
Since the frequency near 0° is raised, the average switching frequency remains unchanged. Therefore, no change occurs in noise, etc.

[0011]

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 shows an inverter on/off signal generation circuit. In FIGS. 1 to 3, 11 is a sine wave generation circuit;
12 is a variable frequency triangular wave generation circuit that generates a variable frequency triangular wave b whose frequency is low near 0° and 180° of the sine wave a and whose frequency is high near 90° and 270°, 131;
133 is a comparator that compares the sine wave a and the triangular wave b and creates control signals S1 and S3 for switching elements SW1 and SW3. 142 and 144 are comparators that create control signals S2 and S4 for switching elements SW2 and SW4 from the sine wave. , 151, 153 are signals S1, S3, S2, S
4 is an arm short-circuit prevention circuit (Fig. 6) which inputs signals S1', S3', S2', and S4', and outputs signals S1', S3', S2', and S4'.
', S2', and S4' are gate drive circuits (not shown), respectively.
Each switching element SW of the inverter 2 in FIG.
It is configured to control conduction of SW1 to SW4.

According to this on/off signal generation circuit, 0°
Since the width of the on-pulse V1 created near , 180° is wide, even if the rising part is delayed by the arm short circuit prevention circuits 151 and 153 and the pulse width is shortened, the on-pulse V1 generated near 0°, 180°, as shown in FIG. The on-pulse V3 near 180° never disappears.

[0014] Therefore, the output voltage Vout of the inverter controlled by the signals S1', S3', S2', and S4' created by this on/off signal creation circuit is not distorted near the zero cross and becomes close to a sine wave. .

[0015]

[Effects of the Invention] Since the present invention is constructed as described above, it produces the following effects.

(1) The on-pulse width near 0° and 180° of the comparison sine wave becomes longer, and the on-pulse near 0° and 180° does not disappear in the latter stage of the short-circuit prevention circuit.
The output voltage waveform is improved.

(2) By lowering the frequency of the variable triangular wave near 0° and 180° of the comparative sine wave and increasing it near 90° and 270°, the average switching frequency of the switching elements of the inverter is almost the same as the conventional method. By doing the same, the noise generated by the inverter can be made almost the same as in the conventional method.

(3) The triangular wave generation circuit currently has ROM and D/
A combination of A converters is often used, and the variable frequency triangular wave can be executed by simply changing the contents of this ROM, so distortion near the zero cross of the output voltage can be suppressed with almost the same circuit configuration as the conventional one.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an inverter on/off signal generation circuit according to an embodiment of the present invention.

FIG. 2 is a block circuit diagram showing the main circuit of the inverter.

FIG. 3 is a waveform diagram illustrating the principle of on/off signal generation of the present invention.

FIG. 4 is a waveform diagram illustrating an on-pulse near 0° of a comparison sine wave.

FIG. 5 is a waveform diagram illustrating the principle of on/off signal generation in the conventional method.

FIG. 6 is a block circuit diagram showing an arm short circuit prevention circuit.

FIG. 7 is a waveform diagram showing voltages at various parts of the arm short-circuit prevention circuit.

FIG. 8 is a waveform diagram illustrating an on-pulse according to a conventional method.

[Explanation of symbols]

2...Inverter 11...Sine wave generation circuit 12...Variable frequency triangular wave generation circuit

Claims (1)

[Claims] 1. In an inverter, the output of an on/off signal generation circuit that compares a sine wave and a high-frequency triangular wave is outputted through an arm short circuit prevention circuit to control switching elements of the inverter, the triangular wave is compared with a sine wave. The frequency becomes low near the phase 0° and 180°,
A method for suppressing distortion of an output voltage waveform of an inverter, characterized in that a variable frequency triangular wave whose frequency increases near 90° and 270° is used to suppress distortion near zero crossing of the inverter output voltage.