JPS585596B2 - inverter circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter circuit and an ignition method, and its purpose is to control load voltage by using a pulse width modulation method (hereinafter referred to as PWM method) and to achieve a low DC input voltage. It is an object of the present invention to provide an inverter circuit that can reliably commutate current with a small-capacity commutating capacitor even in cases where the output side is short-circuit protected and that filtering is easy.

FIG. 1 shows a conventional inverter circuit.

In FIG. 1, E is a DC power supply, Th1 to Th4 are thyristors, T is a transformer, F is a filter circuit, and 1 is a load.

In FIG. 1, commutation circuits (not shown) are connected to the thyristors Th1 to Th4, so that Thl and Th2 or Th3 and Th4 are alternately turned on and off.

Therefore, by properly firing the thyristors Thl to Th4, a large number of rectangular waves as shown in FIG. 2 can be generated in the primary winding of the transformer T.

When the width of this rectangular wave voltage is changed, the average value curve v
1 can be changed to control the output voltage of the inverter.

This voltage control method is called a PWM method.

By making the curve V1 close to a sine wave, the filter circuit F can be made smaller with respect to the sine wave voltage load 1.

However, the voltage charged in the commutating capacitor used in Figure 1 is approximately equal to the voltage of the DC voltage E, so when the voltage of the DC power supply E is low, the commutating capacitor must have an extremely large capacity. was there.

As an inverter to solve these drawbacks, an inverter shown in FIG. 3 using the PWM method has been proposed, and our company has already applied for a utility model registration under Utility Model Application No. 142503/1983.

In the inverter shown in Figure 3, C1 is a commutating capacitor, N
1 is the neutral point of the primary winding of the transformer T.

In the inverter shown in Figure 3, the commutation capacitor C1 is charged to a voltage approximately twice that of the DC power supply E, and as a result, sufficient commutation energy is stored in the capacitor C1, so that the voltage of the DC power supply E increases. Even when the current is low, there is an advantage that commutation can be performed reliably with a small capacitor.

However, in the inverter shown in Fig. 3, when using the PWM method, the output voltage of the transformer T becomes a rectangular wave as shown in Fig. 4, and since a negative rectangular wave also exists during the positive half-wave voltage period, the filter circuit F As the voltage increases, even if the output voltage of the inverter is reduced to zero when the load is shorted, a harmonic voltage, that is, a positive rectangular wave and a negative rectangular wave of approximately the same width alternate in the half cycle period on the output side of the transformer T. If the impedance of the Urahami circuit F to harmonics is small, the short-circuit current of the harmonics becomes considerably large.

The present invention combines two inverters as shown in FIG. By generating only a positive square wave and only a plurality of negative square waves during the negative half-wave period,
Eliminating the drawbacks of the inverters shown in Figures 1 and 3, the load voltage can be controlled using the PWM method, and even when the DC current length voltage is low, commutation can be performed reliably using a small-capacity commutation capacitor, and output side short circuits can be achieved. This is an inverter circuit that is easy to protect and filter.

An embodiment of the inverter circuit according to the present invention is shown in FIG.

In FIG. 5, C2 is a commutating capacitor TI, T2 is a transformer, Nl and N2 are the neutral points of the primary windings of the transformer TI and T2, respectively, and IVi and Iv2 are inverters similar to the inverter shown in FIG. A feedback circuit for feeding back the inertial current of the load to the DC power supply side is provided, but it is not shown.

Both inverters IV1 and IV2 are connected to the voltage of the DC power supply E and are connected to generate an AC voltage in the secondary windings of the transformers T1 and T2, respectively.
The two secondary windings are connected in series with each other, and are connected so as to supply the output to the load 1 via the filter circuit F.

In FIG. 5, thyristors Thl and Th2 are turned on alternately so that the output voltage of the transformer T1 becomes as shown in FIG.
When h3 and Th4 are turned on alternately, a voltage as shown in FIG. 6C is applied to the input side of the filter circuit F.

The voltage shown in 8 is the sum of voltage A and voltage A.

In the voltage waveform shown in C, only a positive rectangular voltage waveform occurs during the positive half-wave period, and only a negative rectangular voltage waveform occurs during the negative half-wave period.

In FIG. 6, v3 represents the average value curve of a rectangular wave, and in FIG.
When the thyristors Th3 and Th4 are turned on alternately so that the output voltage of the transformer T2 becomes E in Fig. 1, the voltage shown in Fig. 7 is applied to the input side of the waveform circuit F. The voltage is the sum of and E.

In FIG. 7, v4 indicates an average value curve of a rectangular wave.

Also in the voltage waveforms shown in (b), only positive rectangular voltage waveforms occur during the positive half-wave period, and only negative rectangular voltage waveforms occur during the negative half-wave period.

The voltage waveforms shown in C and B contain harmonic voltages because the rising or falling voltage value of each rectangular wave can be reduced to 1/2 of that of the rectangular wave in FIG. 4 at the same output voltage effective value. Since the ratio can be made small, the filter circuit F can be made small.

In addition, when the load is short-circuited, the output voltage waveform of the transformer T1 and the output voltage waveform of the transformer T2 are made to have opposite phases to each other.
Since the voltage of the sum of T1 and T2 can be made zero and not only the fundamental wave but also the harmonic current flowing through the load can be made zero, short-circuit protection on the output side can be easily performed.

Furthermore, regarding the commutation of the thyristor, the commutation capacitor can be charged to a voltage twice that of the DC power source E, as shown in FIG. 3, so commutation errors are unlikely to occur even with a small capacity capacitor.

As explained above, in the inverter circuit according to the present invention, only a positive rectangular wave voltage is generated during the positive half-wave period, and a negative rectangular wave voltage is generated during the negative half-wave period.
Since the WM method can be adopted, filtering becomes extremely easy.

Even when the DC input voltage is low, reliable commutation is possible with a small-capacity commutation capacitor, and even in the event of a load short-circuit, the output voltage phases of the two inverters can be reversed to make the load voltage zero, so there is no short-circuit. Easy to protect.

[Brief explanation of drawings]

Figure 1 is a conventional inverter circuit diagram, and Figure 2 is a circuit diagram of a conventional inverter.
Figure 3 is an inverter circuit diagram using two thyristors. Figure 4 is an illustration of the output voltage waveform when PWM control is performed using the inverter in Figure 3. Figure 5 is an illustration of the output voltage waveform when PWM control is performed using the inverter in Figure 3. Embodiment circuit diagrams of the inverter circuit according to the present invention, FIG. 6 and FIG. 1 are explanatory diagrams of the operation in FIG. 5. In the figure, E is a DC power supply, Thl to Th4 are thyristors, and T
, TI, T2 are transformers, F is a filter circuit, and CI, C2 are commutating capacitors.

Claims (1)

[Claims] 1. An inverter that generates an alternating current voltage on the output side of the transformer by alternately applying a direct current power supply voltage to two windings that are divided into two at the neutral point of the primary winding of the transformer using a thyristor having a commutation circuit. By combining two or more inverters, synchronizing the basic waveform of each inverter with the basic waveform of the output of the transformer, making the firing of each inverter different, and connecting the output sides of the inverters in series, positive half-wave An inverter circuit characterized in that it generates only a plurality of positive rectangular waves during a period and only a plurality of negative rectangular waves during a negative half-wave period.