JPS59198880A - Sinusoidal wave generating inverter circuit - Google Patents

Abstract

PURPOSE:To reduce the size and weight of an inverter circuit by combining rectangular wave signals of frequencies having twice differences of the frequency of a sinusoidal wave to be obtained, applying it to a rectifier which alternately operates at every zero beat to generate a sinusoidal wave. CONSTITUTION:When the frequency of a sinusoidal wave to be obtained is f0 from inverters 41, 42, rectangular wave signals of frequencies f+f0, f-f0 having twice differences of the frequency are outputted, applied to the primary windings of transformers 43, 44, the secondary winding is connected in series and combined. The beat signal of 2f0 is added to rectifiers 45, 46 when the rectifying direction is inverted, alternately driven by a signal of a zero beat detector 47, smoothed by a capacitor 48, thereby obtaining a sinusoidal wave output. Accordingly, the frequencies of inverters 41, 42 are set to high value to reduce the size and to decrease the harmonic wave components.

Description

[Detailed description of the invention] The present invention relates to a sine wave generating inverter circuit.

As is well known, various sine wave generating inverter circuits have been developed. FIG. 1 shows a conventional circuit 111 of this type. rll
*From 116, rectangular wave signals el+e2 of the same frequency whose output timings are shifted by a predetermined time as shown in FIG.
e6 is output. These output signals else! ~
e6 is the primary coil 121.1 of transformer 12.13-17
3. ~771, respectively, and these transformers 12.
13-17 series connected secondary coils 12. ．． 132
~172, the signal el+e! ""e6 is synthesized. This combined signal (FIG. 2e) is supplied to a low-pass filter 18 to remove harmonic components.

By the way, in the above configuration, in order to make the waveform output from the low-pass filter 18 closer to a sine wave, it is necessary to increase the number of inverter circuits. However, the firing phases of these inverter circuits must be controlled at different timings, as shown by tl-ts in Figure 2, so when the number of inverter circuits increases, these controls become extremely complicated. It is something. Further, even if it were possible to reduce low-order harmonic components by increasing the number of inverter circuits, a low-pass filter would be required, and a large capacitor and capacitor would have to be used.

Therefore, in order to solve these drawbacks, switching elements such as thyristors are turned on and off many times as shown in (b) of the same figure during one period of the rectangular wave output signal of the inverter circuit shown in the Pal diagram (,). A PWM modulated signal is obtained, and low-order harmonic components are removed from this 4M modulated signal to obtain a signal that approximates a sine wave as shown in FIG. 4(c).

However, in order to reduce the frequency to a higher level, it is necessary to increase the switching frequency of a thyristor or the like that is turned on and off within one cycle of the signal output from the inverter circuit. However, switching elements such as thyristors have a limit to the frequency at which they can operate, and require commutation circuits suitable for that frequency, and are subject to various restrictions on circuit configuration.

This invention was made based on the above circumstances, and its purpose is to be able to set the output frequency of the inverter circuit higher than the desired sine wave, to make the circuit smaller, lighter, and less expensive, and to reduce switching elements. The present invention aims to provide a complete sine wave generating inverter circuit that can operate reliably within the permissible frequency range and obtain a sine wave with few harmonic components.

An embodiment of the present invention will be described above with reference to the drawings.

In FIG. 4, inverter circuits 41 and 42 have a well-known configuration, and if the frequency of the sine wave to be obtained from these inverter circuits 41 and 42 is fo (Hz), the difference is twice this frequency. Frequency f+fo, f
A rectangular wave signal of fo (Hz) is output.

The square wave signals output from these in/output circuits 41, 42 are transmitted to the primary windings 430, 44, . are supplied respectively. The secondary windings ``'2+442'' of this transformer 43 and 44 are connected in series, and the - secondary winding 442 is connected in series.
31a 441 is applied to these secondary windings 4J2, 44. is synthesized by This synthesized signal, ie, the 2fo (Hz) beat signal shown in FIG. 5(a), is transmitted to the secondary winding 43. ．． 44
The first . Second rectifier circuit 45
46°. These first. Second rectifier circuit 45
．． 46 are respectively GTO ()1 to -) turn off)
This is a bridge rectifier circuit consisting of thyristors 451 to 454 and 461 to 464, and these rectifier circuits 45 and 46 have rectifying directions opposite to each other.

On the other hand, the output signals of the inverter circuits 41 and 42 are respectively supplied to a zero beat detection circuit 47. This detection circuit 47 is composed of, for example, a comparator consisting of an operational amplifier and a logic circuit, and each inverter circuit 4
The moment when the difference between the output voltages 1 and 42 becomes @O# is detected, and each time this zero beat is detected, a pulse signal of opposite polarity shown in FIGS. 5(b) and 5(c) is output. The output pulse signal of this zero beat detection circuit 47 is supplied to the first and second rectifier circuits 45 and 46, and this pulse signal causes the GTO thyristors 451 to 454 and 461 to 464 to
are turned on and off alternately. Therefore, these first.
The second rectifier circuits 45 and 46 output rectified signals as shown in FIG. 5(a). This rectified signal is smoothed by a capacitor 48 to smooth it to the frequency f', and as shown in FIG. considered to be waves.

According to the above configuration, two interface circuits 47.42
The frequency of the rectangular wave signal outputted from the square wave signal is set to a frequency that is twice the frequency of the sine wave to be obtained. Therefore, if this relationship is maintained, the inverter circuits 41 and 42
This has the advantage that the output frequency can be set regardless of the sine wave to be determined. Moreover, by setting the output frequency high within the allowable range of the switching elements, the inverter circuits 41, 42f can be made smaller and lighter.

Furthermore, the envelope of the signals synthesized by the transformers 43, 44 becomes a sine wave regardless of the output waveform of the inverter circuits 41, 42. Therefore, if the polarity is reversed every zero beat and rectified, and then smoothed by the capacitor 48, a fixed string with few harmonic components can be produced without using a complicated filter consisting of a large capacitor and a capacitor as in the past. It is possible to get waves.

Furthermore, the first. The GTO Cyrisks 451 to 454.4f to 464 constituting the second rectifier circuits 45, 46 are each operated by a pulse signal having the same frequency as the desired sine wave. Therefore, since it is operated within the permissible frequency range, it is possible to obtain stable operation.

Furthermore, the output frequencies of the inverter circuits 41 and 42 are set relatively high compared to the frequency of the desired sine wave, and the first . Since the second rectifier circuits 45 and 46 are provided, commutation errors and the like will not occur in the inverter circuits 41 and 42 due to influence from the output side.

As detailed above, according to the present invention, the output frequency of the inverter circuit can be set higher than the desired sine wave, the circuit can be made smaller and lighter, and the switching elements can be reliably maintained within the permissible frequency range. Accordingly, it is possible to provide a sine wave generating inverter circuit that can operate in a similar manner and can generate a sine wave with few harmonic components.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an example of a conventional sine wave generating inverter circuit, Fig. 2 is a waveform diagram shown to explain the operation of Fig. 1, and Fig. 3 is a sine wave generating inverter circuit different from Fig. 1. 4 is a configuration diagram showing an embodiment of the sine wave generating inverter circuit according to the present invention, and FIG. 5 is a waveform diagram shown to explain the operation of FIG. 4. It is. 41.42... Inverter circuit, 43.44... Transformer, 45.46... 1st. second rectifier circuit, 47.
...Zero beat detection circuit, 48...capacitor.

Claims (1)

[Claims] Two inverter circuits that each generate a signal set to twice the sine wave required by their frequency difference, a means for synthesizing the output signals of these inverter circuits, and a means to which the synthesized signal is supplied and rectified in different ways. The first one has a direction. A second rectifier circuit, a capacitor for smoothing the output signals of these rectifier circuits, and a zero beat are detected from the output signals of both the inverter circuits, and for each zero beat, the first
．． A sine wave generating inverter circuit comprising means for alternately driving the second rectifier circuit.