JPH01129778A - Protecting circuit for inverter - Google Patents

Abstract

PURPOSE:To prevent a short-circuit damage from increasing by not operating an inverter controlling circuit by operation inhibiting means for storing when the short-circuit damage of switching means is detected, it. CONSTITUTION:An inverter device has a converter 1 for rectifying 3-phase AC voltages into a DC voltage, a smoothing capacitor 2, a DC current detector 3 and an inverter circuit 4 for converting the DC voltage to 3-phase AC voltages of predetermined frequency, and supplies it to a load motor 5. Further, it has an inverter control circuit 6, a short-circuit damage detector 7 and a temporary damage memory circuit 8. A protecting circuit stores, when it detects the short- circuit damage of a power transistor at the time of reenergizing a power source after the detector 7 generates the malfunction of the inverter circuit 4, it in the memory circuit 8, and inhibits to operate the inverter control circuit.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a protection circuit for an inverter, and more specifically, to prevent damage to an inverter circuit from expanding when switching means constituting the inverter circuit is damaged by a short circuit. This invention relates to a protection circuit for an inverter.

[Conventional technology] FIG. 3 is a schematic diagram of a conventional inverter device.

In Figure 3, (1) is a converter circuit that rectifies three-phase AC voltage to DC voltage, and (2) is converter circuit (1).
(3) is a DC current detector that detects the current output by the converter circuit (1); (4) is a plurality of power transistors U 1 and U 2 .

An inverter circuit (5) that converts a DC voltage into a three-phase AC voltage of a predetermined frequency by controlling Nv and VSw on and off at a predetermined timing is a control target of the inverter device, Inverter circuit (4)
This is a load motor that is driven by the three-phase AC voltage output by the motor.

Next, the operation of the conventional inverter device will be explained.

When the power is turned on, the converter circuit (1) rectifies the three-phase AC voltage into a DC voltage, and the electrolytic capacitor (2) absorbs the ripple voltage of the DC voltage and outputs it to the inverter circuit (4). Furthermore, the power transistor U p ””
By controlling WN on and off at a predetermined timing, the inverter circuit (4) converts the DC voltage with ripple voltage absorbed into a three-phase AC voltage of a predetermined frequency and outputs it to the load motor (5). and rotates the load motor (5).

In this inverter device, when the load on the load motor (5) suddenly increases or the power transistor U p "" W N is damaged, the DC current detector (3) detects an overcurrent and the inverter control circuit (not shown) is activated. (4) stops the operation of the inverter circuit (4) upon detection of overcurrent. In this way, in the inverter device, when the DC current detector (3) detects an overcurrent, the inverter circuit (4)
By stopping the operation of the inverter circuit (4)
It has a protective function that protects the

[Problems to be solved by the invention] However, depending on the load conditions, the power transistor UP-
WN may be partially damaged. FIG. 4 shows a part of the inverter circuit (4) shown in FIG. 3. In addition, in FIG. 4, (11) is the converter circuit (1)
from the inverter circuit (4) via the electrolytic capacitor (2).
) indicates the voltage input to the circuit.

Now, assume that the power transistor UP is damaged and the inverter control circuit stops the operation of the inverter circuit (4). When the operation of the inverter circuit (4) stops,
- You will have to turn off the power to the inverter device and then turn it on again.

When the power is turned on again, the inverter circuit (4) operates and a pulsed base current IB of a predetermined frequency flows through the power transistor U as shown in Fig. 5, causing damage to the power transistor U. Therefore, a current as shown in FIG. 4 flows through the power transistors U and UN.

Therefore, the DC current detector (3) detects the overcurrent again, but at this time, the power transistor UN is loaded with voltage and current as shown by the solid line in Figure 6, and the power transistor UN is loaded with the voltage and current shown by the dotted line in Figure 6. There is a problem in that the power transistor UN is damaged beyond the safe operating range of the power transistor UN as shown in (a), resulting in a power supply short-circuit damage state.

Furthermore, if the power transistor UN is damaged following the power transistor UP, there is a problem that a fire may occur in the worst case scenario.

The present invention has been made to solve the above problems,
Power transistor U forming inverter circuit (4)
It is an object of the present invention to provide an inverter protection circuit that does not operate the inverter circuit (4) even if the power is turned on again when the p-WN is damaged.

[Means for solving the problem] The inverter protection circuit according to the present invention is a short-circuit damage protection circuit that detects short-circuit damage of a plurality of switching means constituting the inverter circuit when the power is turned on again after an abnormality occurs in the inverter circuit. a detection means, a storage means for storing detection of short-circuit damage of the switching means, and an inverter control circuit for controlling the plurality of switching means on and off at a predetermined timing when the storage means stores the short-circuit damage of the switching means. and an operation prohibition means that prevents the operation.

[Function] In the inverter protection circuit configured as described above, when the short-circuit damage detection means detects short-circuit damage in the switching means when the power is turned on again after an abnormality has occurred in the inverter circuit, the storage means memorizes this and prohibits operation. The means prevents the inverter control circuit from operating according to the stored contents of the storage means.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an inverter device using an inverter protection circuit according to the present invention. In Figure 1, (
1) is a converter circuit that rectifies three-phase AC voltage to DC voltage, (2) is a smoothing electrolytic capacitor that absorbs the ripple voltage of the DC voltage output by converter circuit (1), (
3) is a DC current detector that detects the current output by the converter circuit (1), and (4) is a plurality of power transistors U.
U.

The inverter circuit (5) converts DC voltage into three-phase AC voltage with a predetermined frequency by turning on and off P' N V SV 1W 1WN at a predetermined timing. a load motor (6) driven by the three-phase AC voltage output by the circuit (4);
is an inverter control circuit that turns on and off the power transistors UP to WN constituting the inverter circuit (4) at a predetermined timing, and (7) is the power transistor U - W
(8) is a memory circuit such as a flip-flop that temporarily stores information that the power transistors U, -WN are damaged.

Note that the inverter control circuit (6) is the inverter circuit (4).
) is in operation, it has a function of resetting the memory circuit (8) to prevent malfunction.

Next, Figure 2 shows the short circuit damage detection circuit (7) shown in Figure 1.
2 is a circuit diagram showing a part of the power transistor U and UN, and is used to detect damage to the power transistors U and UN.

In Fig. 2, (11) is the DC voltage input from the converter circuit (1) to the inverter circuit (4) via the electrolytic capacitor (2), (12), (13a), (13
b) is a resistor that divides the DC voltage input to the inverter circuit (4), (14a) and (14b) are the voltage divided by the resistors (12), (13a), and (13b) and the reference, respectively. The voltage V 1v is compared, and when the divided voltage is larger than the reference voltage V 1v ref
a voltage comparator that outputs a low level rLJ detection voltage to a refb;
(15) is a DC power supply that outputs a voltage of a predetermined magnitude, (
16a) and (17a) divide the output voltage of the DC power supply (15) and convert the reference voltage V to r of the voltage comparator (14a).
efa Voltage dividing resistor input to non-inverting terminal, (16b), (17
b) is a voltage dividing resistor that divides the output voltage of the DC power supply (15) and inputs the reference voltage V to the non-inverting terminal of the voltage comparator (14b); (18a) and (18b) are photocouplers; (19a), (19b), (20a),
(20b), (21a), and (21b) are resistors.

Next, the operation of the circuit shown in FIG. 2 will be explained. First, when power transistors U and UN are normal,
The voltage at point b divided by the resistors (12), (13a) and (13b) is approximately 1/2 of the output voltage of the DC power supply (15).
It has become. In this case, the voltage input to the inverting terminal of the voltage comparator (14a) is smaller than the reference voltage V input to the non-inverting terminal, so the voltage comparator (14a) detects the high level rHJ detection voltage. Output. Therefore, in the photocoupler (18a), the light emitting diode is not lit and the phototransistor is off, so the output terminal (7a) is at high level rH.
It's a J. Similarly, since the voltage input to the inverting terminal of the voltage comparator (14b) is higher than the reference voltage V refb input to the non-inverting terminal, the output terminal (7a) is at a high level rHJ.

Now, if the power transistor U is damaged in conduction, the voltage input to the inverting terminal of the voltage comparator (14a) is equal to the reference voltage V input to the non-inverting terminal.
The voltage comparator era (14a) outputs a detection voltage of low level rLJ.

Therefore, the photocoupler (18a) lights up the light emitting diode, turns on the phototransistor, and outputs the output terminal (7).
a) becomes low level rLJ. Conversely, if the power transistor UN is damaged in conduction, the voltage comparator (1
The voltage input to the inverting terminal 4b) becomes smaller efb than the reference voltage V input to the non-inverting terminal, and the voltage comparator (14b) outputs a detection voltage of high level rHJ. Therefore, the photocoupler (18b)
The light emitting diode lights up, the phototransistor turns on, and the output terminal (7a) becomes low level rLJ.

In this way, when the power transistor UP or UN is damaged due to conduction, the output terminal (7a) becomes low level rLJ, so that the above-mentioned power supply short circuit can be prevented from occurring.

In addition, in this example, photocouplers (18a) and (18
Although the outputs of b) are connected and treated as one signal, they may be output separately and used to indicate the location of a damaged power transistor, etc.

Further, although a DC amplifier is used as the voltage comparator in this embodiment, a comparator, a shunt regulator, etc. may also be used.

[Effects of the Invention] As explained above, according to the present invention, when the short-circuit damage detection means detects short-circuit damage of the switching means when the power is turned on again after an abnormality occurs in the inverter circuit, the storage means detects the short-circuit damage of the switching means. The operation prohibiting means prevents the inverter control circuit from operating according to the memory contents of the storage means, so even if an abnormality occurs in the inverter circuit and the power is turned off and then turned on again, This has the effect of providing an inverter protection circuit that can prevent short-circuit damage to the switching means from expanding.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an inverter device using an inverter protection circuit according to the present invention, FIG. 2 is a circuit diagram showing a part of the detection circuit shown in FIG. 1, and FIG. 3 is a block diagram of a conventional inverter device. A schematic diagram, FIG. 4 is an explanatory diagram of conduction damage of the power transistor, and FIGS. 5 and 6 are explanatory diagrams of the operation of the power transistor. In each figure, 1 is a converter circuit, 2 is an electrolytic capacitor, and 3 is a converter circuit.
is a current detector, 4 is an inverter circuit, 5 is a load motor,
6 is an inverter control circuit, 7 is a short-circuit damage detection circuit, and 8 is a memory circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (4)

[Claims] (1) It has an inverter circuit composed of a plurality of switching means, and an inverter control circuit that converts a DC voltage into an AC voltage of a predetermined frequency by controlling the plurality of switching means on and off at a predetermined timing. In an inverter protection circuit, a short-circuit damage detection means detects short-circuit damage of the plurality of switching means when the power is turned on again after an abnormality occurs in the inverter circuit, and a storage means stores the detection of short-circuit damage of the switching means. An inverter protection circuit comprising: an operation inhibiting means for disabling the inverter control circuit when the storage means stores short-circuit damage of the switching means. (2) The short-circuit damage detection means is provided for each of the plurality of switching means, and detects short-circuit damage of the corresponding switching means by comparing a preset reference voltage and the output voltage of the inverter circuit. The inverter protection circuit according to claim 1, which is a plurality of comparison means for detecting. (3) The inverter protection circuit according to claim 2, wherein each of the plurality of comparison means receives the output voltage of the inverter circuit through a voltage dividing resistor. (4) The inverter protection circuit according to claim 2, wherein the plurality of comparison means outputs short-circuit damage of the switching means to the storage circuit via a photocoupler.