JPS5815472A - Overload protecting device for inverter - Google Patents

Abstract

PURPOSE:To effectively prevent a shortcircuit trouble without using expensive semiconductor breaker and current limiting resistor by detecting the defect, limiting the output current for the prescribed period of time and then softly starting an inverter. CONSTITUTION:When a shortcircuit defect occurs at the load side, an overcurrent detector 15 operates to input a set signal to a flip-flop 16, and the output of which is applied to a gate control circuit 14, a constant-voltage circuit 11, a constant-current control circuit 12, and a timer 17. As a result, the output current is abruptly reduced to zero, and the timer 17 starts operating. After the prescribed period of time is elapsed, a reset signal is inputted to the filp- flop 16, the output of which releases the OFF signal to the gate control circuit 14, an ON signal is applied to an inverter 2, thereby softly starting the inverter 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for an inverter device against overcurrents such as load short-circuit accidents.

In general, in static inverter devices, the overload quantity is relatively small, and if the load current exceeds the overload tolerance, the semiconductor elements that make up the device are often destroyed. Protective devices are used.

As such a protection device, for example, there is a semiconductor breaker that has a high-speed breaker function and is provided between the inverter device u and the load. However, in the case of semiconductor circuit breakers,
Problems include that they are expensive and that they cannot be applied to loads such as motors or transformers that draw excessive current at startup. There is a device using a current limiting resistor to solve the latter problem, but this requires a large load and, depending on the operating time, becomes an expensive and large device.

The purpose of the present invention is to reliably protect an inverter device without using an expensive protection device such as a semiconductor circuit breaker, and also to make it possible to apply a load such as a motor or transformer through which a starting inrush current flows. The purpose of the present invention is to provide a load protection device.

An embodiment of the present invention will be described below with reference to FIG. FIG. 2 is an operational waveform diagram for explaining the operation of each part of the embodiment shown in FIG. In FIG. 1, 1 is a DC power supply, 2 is an inverter, 4 is a load, 3 is an OT that detects the load current, 11 is a constant voltage control circuit that controls the output voltage of the inverter 2 to a constant @1, and 12 is the inverter 2 A constant current control circuit 13 limits the level of the output O8 of the constant voltage control circuit 11 in order to suppress the output current (load current) of the constant voltage control circuit 11 to a predetermined limit current value or less; A phase shifter that determines the firing phase of the inverter 2, 14 a gate control circuit that controls on and off of the inverter 2;
6 is an RS flip-flop, 17 is a timer that starts operation by the "1'' output of the T (S flip-flop 160), and 15 is a timer that detects an overcurrent on the output side caused by a short-circuit accident on the load side of the inverter 2, etc. , I:t This is an overcurrent detection circuit that provides a set signal O8 to the S flip-flop 16.

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to the operational waveform diagram shown in FIG. In FIG. 2, symbols AS to H8 indicate waveforms of respective parts corresponding to the same symbols in FIG. The limiting current value TH of the constant current control circuit 12 and the detection level IC of the overcurrent detection circuit 15 are both determined by the overload withstand capacity of the inverter 2, and usually To ) J
rel set to be n. RS flip flop 16
operates using the output O8 of the overcurrent detection circuit 15 as a set signal and the output 1/IS of the timer 17 as a reset signal, and its output 1)S (“1” output) is sent to the gate control circuit 14. is an off command, and the output G is sent to the constant voltage control circuit 11 and the constant voltage control circuit 12.
This command is given as a reset command to rapidly lower S and INS to the minimum level, and is given to the timer 17 as an operation start command.

Then, the load fits at time t1! If a short-circuit accident occurs at +, the output current of inverter 2 (Fig. 2 03))
As soon as the overcurrent detection circuit 5 exceeds the detection level Ia of the overcurrent detection circuit 15, the overcurrent detection circuit 5 operates, and its output O8 (second
Figure (C)) is given as the RSS flip-flop 16 set signal, and the output 1]s(
FIG. 2 ffJ) shows the gate control circuit 14 as described above.
, constant voltage control circuit 11, constant current control circuit 12, and timer 17. As a result, at time t2, inverter 2
is given an off command (prompted in Figure 2), and the output voltage (second
Figure (A)) suddenly drops to the floor and becomes zero voltage, and as a result, the output current also rapidly reaches zero, and on the other hand, the outputs O8 and H8 of the constant voltage control circuit 11 and the constant light control circuit 12 (the 2 (q and FIG. 2 (Fl)) rapidly decrease to the minimum level, and the timer 17 starts operating. Thereafter, the timer 17 starts operating at the time when the set time T has elapsed (
At time ts), the output ES (m2 diagram (average) is given as a reset signal to the RS flip-flop) 6, and its output DS
is reset and returns to 0'' from °1°'. When the output DS of the RS flip-flop 16 returns to 0'', the off command to the gate control circuit 14 is released and the inverter 2 is given an on command. At the same time, the reset command to the constant voltage control circuit 11 and constant current control circuit 12 is also canceled.

As a result, the output O8 of the constant voltage control circuit 11 gradually increases from the minimum value as an initial value, the inverter 2 performs a so-called soft start, and the output voltage As gradually increases. If the short-circuit accident continues, as the output voltage As increases, the output current BS also increases, but when this reaches the limit current value TH of the constant current control circuit 12, the control operation of the constant current control circuit 12 causes The output current BS is suppressed to the limit current value TH, and the output voltage As does not rise any further. (The time constant of the inverter's soft start is selected to be a sufficient time for constant current control to operate.) If the short-circuit fault has been removed, inverter 2 will perform constant voltage control after soft start. Constant voltage control is performed by the control operation of the circuit 11. Furthermore, even if the aforementioned short-circuit accident continues, if the short-circuit accident is subsequently canceled due to the tripping of the breaker on the load side (not shown), the constant voltage control operation is restored from the constant current control switch. The output width pressure As of the inverter 2 recovers to the constant voltage setting level. That is, in any case, the output 'i:li current of the inverter 2 is suppressed below the limit 'spiral current value of the constant current control circuit I2, and the output current (
The constant voltage control operation and the constant current control operation are automatically selected and switched depending on the level of the load (current).

According to the above-mentioned overload protection device installed to the left of the inverter, which operates in this manner, the inverter directly can be reliably protected from a short-circuit accident or overload of the load 111 without using an expensive semiconductor breaker.

On the other hand, even for a load such as a motor or a transformer in which a starting inrush current flows, it is possible to smoothly turn on the load through the current limiting operation and soft start operation as described above without using a current limiting resistor.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an overload protection device for an inverter device according to the present invention, and FIG. 2 is an operation waveform diagram illustrating the operation of the embodiment of FIG. 1. ■...DC box; source, 2...inverter 3...
・OT 4... Load 11... Constant voltage control circuit, 12... Constant current control circuit 13... Phase shifter, 14... Gate control circuit 15... Overcurrent detection circuit. 16, -0Rs Fritzbufu [Koppu 17... Timer. (7317) Agent: Patent Attorney Nori Konan Yu (Haka1)
name) 1st cause diagram 2

Claims (1)

[Scope of Claims] Impark that converts direct current to alternating current, a constant voltage control circuit that controls the output voltage of the inverter to a constant value, and a constant current control circuit that limits the output current of the inverter to a predetermined current limit value or less. The inverter device includes an overcurrent detection circuit that detects an overcurrent caused by a short circuit accident or overload on the load side of the inverter device, and when the overcurrent detection circuit is in operation, turns off the inverter to reduce the load current. suppressing the current to below the limit current value of the constant current control circuit, resetting the outputs of the constant voltage control circuit and the constant current control circuit to a minimum value, and then turning on the inverter after a predetermined period of time has elapsed; A control circuit having a function of canceling the reset of the constant voltage control circuit and the constant current control circuit is provided, and the output voltage of the inverter is gradually increased by the operation of the constant voltage control circuit or the constant current control circuit. 1. An overload protection device for an inverter device, characterized in that a current less than a current limit value of the constant current control circuit is supplied to the load until a short circuit accident or overload is canceled.