JPH0817575B2 - Inverter protection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention comprises an inverter protection system, in particular a bridge-connected switching element, to which a load including a capacitor is connected. In an inverter circuit, the present invention relates to an inverter protection method in which the polarity of the output of the oscillation circuit controlling the switching element is compared with the polarity of the voltage generated in the load, and a rest period is provided at the on / off switching period of the switching element. .

[Prior Art] Conventionally, an inverter circuit having a configuration as shown in FIG. 3 has been known.

In FIG. 3, reference numerals 1-1 to 1-4 are transistors, 2-1 to 2-4 are free-wheeling transistors, respectively.
Diode, 3 is a load and 3-R is a resistive load 3-C
Is a capacitor load and 4 is a DC power supply.

Conventionally, an inverter circuit having the above-mentioned configuration is known, but when the capacitor load 3-C is connected as a load, the following problems are inherent.

[Problems to be solved by the invention]

In the case where the capacitor load 3-C is connected as shown in FIG. 3, the transistors 1-2 and 1-3 are now turned off, and accordingly, the transistors 1-1 and 1- when 4 and is turned on, a large discharge current, such as Figure 3 illustrated i _c occurs. This is because the transistors 1-1 and 1-4 are turned on when the capacitor load 3-C is charged as shown in (+) and (-) in FIG. This is because the capacitor load 3-C is about to be charged in the opposite direction. FIG. 4 is a time chart showing the situation during this period.

[Means for solving problems]

The present invention solves the above problems, and solves the problems in the above cases by arranging the voltage detection resistor and detecting the polarity of the voltage generated in the load.

FIG. 1 is a principle block diagram of the present invention and constitutes an embodiment of the present invention. Reference numerals 1-1 to 1- in the figure
Reference numeral 4 is a transistor, 2-1 to 2-4 are freewheeling diodes, 3 is a load, and 5-1 to 5-4 are voltage detection resistors. Further, 6 is a polarity detection unit for detecting the polarity of the load voltage, 7 is a rectangular wave oscillation circuit unit, and 8 is a polarity comparison circuit unit.

Operation in the circuit shown in FIG. 1, especially transistor 1
-1 and 1-4 of the first group of switching elements and transistors 1-2 and 1-3 of the second group of switching elements are alternately turned on, which is substantially the same as the conventional configuration. . However, the resistors 5-1 to 5-4 are provided to detect the polarity of the voltage generated on the load 3.

That is, the voltage (RV) on the right side of the load 3 and the voltage (LV) on the left side of the load 3 are extracted, the period of RV−LV ≧ + ΔV is regarded as the first polarity, and the period of LV−RV ≧ + ΔV is determined. Considering the second polarity, the polarity detection unit 6 notifies the polarity comparison circuit unit 8 of this fact.

The rectangular wave oscillation circuit unit 7 emits a rectangular wave output, and the polarity comparison circuit unit 8 compares the polarity of the output of the rectangular wave oscillation circuit unit 7 with the polarity from the polarity detection unit 6. And
The period in which the polarities of both are different corresponds to the period in which the capacitor existing in the load is being discharged. Therefore, only during that period, a rest period is set in which the entire switching element is turned off. I am trying.

[Action]

The above operation status is clarified by the time chart shown in FIG. In FIG. 2, the period of “pause” corresponds to the pause period. Then, the pause period corresponds to a period in which the voltage of the capacitor existing in the load 3 is attenuated by the discharge as shown by the hatching in the figure.

For this reason, after a period in which the capacitor existing in the load 3 is discharged, for example, the set of transistors 1-2 and 1-3 is changed to the set of transistors 1-1 and 1-4. That is, the period in which the capacitor is discharged and the period in which the switching element is turned on and charged are separated, and an excessive current is prevented from flowing.

〔The invention's effect〕

As described above, according to the present invention, in controlling so as to place the above-described pause period, the pause period can be generated by the process of only comparing the polarity of the output of the oscillation circuit unit with the polarity of the load. it can. For this reason, the circuit configuration is much simpler than that of the conventionally known configuration, for example, in which the output waveform itself of the oscillation circuit section is provided with a predetermined voltage zero period when the pause period is set. Become. That is, it is possible to achieve the intended purpose even by digital processing.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention, which constitutes an embodiment of the present invention, FIG. 2 is a time chart explaining its operation, FIG. 3 is a conventional configuration, and FIG. 4 is its operation. The time chart to demonstrate is shown. In the figure, 1 is a switching element (transistor), 2 is a freewheeling diode, 3 is a load, 3-C is a capacitor load, 4 is a DC power supply, 5 is a voltage detection resistor, 6 is a polarity detection unit, and 7 is a rectangle. The wave oscillating circuit section, 8 represents a polarity comparing circuit section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-148591 (JP, A) JP-A-60-249874 (JP, A) JP-A-60-229676 (JP, A)

Claims (1)

[Claims] 1. An inverter circuit comprising a switching element having a freewheeling diode externally attached or built therein, the switching element being bridge-connected, and a load including a capacitor being connected between neutral points of the bridge connection. , Voltage detection resistors are connected in parallel to at least the switching elements existing at non-opposing positions in the bridge connection, and the detection voltage generated on each of the voltage detection resistors is extracted to detect the voltage generated in the load. The polarity is detected, and the polarity is compared with the polarity of the oscillation circuit output that controls the switching element. Based on the comparison result, the polarity of the oscillation circuit output is generated in the load. The period in which the polarity of the applied voltage is different is determined as the rest period, and the rest period In response to the above, an inverter protection method is characterized in that a period during which the switching elements of the second group are not turned on after the switching elements of the first group connected by the bridge are turned off.