JPH0685620B2 - Inverter overcurrent protection device - Google Patents

Description

The present invention relates to an overcurrent protection device for protecting an inverter device from overcurrent.

[Conventional technology]

FIG. 3 is a circuit diagram showing, for example, a conventional overcurrent protection device for an inverter device. In the figure, (1) is a converter unit corresponding to a DC power source for converting AC to DC, and (2) is a converter unit (1 ) Is a smoothing capacitor for smoothing the output, (3) is an anode side busbar connected to the anode of the converter section (1), (4) is an anode side busbar connected to the cathode of the converter section (1), (5 ) Is a voltage-driven upper main transistor, one end of which is connected to the anode-side bus (3), for converting a DC voltage into an AC voltage by a switching operation,
(6) is connected in parallel to the upper main transistor (5),
A voltage-driven upper auxiliary transistor that divides the main current flowing into the upper main transistor (5) at a ratio of 1: N,
(7) is an upper resistor which is connected in series to the upper auxiliary transistor (6) and causes a voltage drop due to the shunted current to indirectly detect the main current. A voltage-driven lower main transistor that is connected to the other end of the upper main transistor (5) and the other end of the upper main transistor (5) is connected to the cathode-side bus (4), and that converts a DC voltage into an AC voltage by a switching operation, 9) is a lower auxiliary transistor connected in parallel with the lower main transistor (8) and has the same function as the upper auxiliary transistor (6), and (10) is connected in series with the lower auxiliary transistor (9), A lower resistor having the same function as the resistor (7), (11) is connected in parallel with the upper main transistor (5), and is a freewheeling diode for protecting the upper transistor (5) from a back electromotive current. , (12) is a three-phase induction motor that is a load, (13) is an output terminal drawn from the connection point of the upper main transistor (5) and the lower main transistor (8), and (14) is the upper main transistor. The gate inputs of the transistor (5), the lower main transistor (8), the upper auxiliary transistor (6) and the lower auxiliary transistor (9) are controlled to perform switching operation, and the upper main transistor (5) and the lower main transistor (8) are also operated. A control circuit that performs control operation such as stopping each switching operation to put into a cut-off state when an overcurrent flows to the (15)
Is a comparing means for detecting an overcurrent state of the upper main transistor (5) and the lower main transistor (8), (16) is a reference voltage generating means for outputting a reference voltage to be compared with the overcurrent, and (17) is The first detecting means composed of the upper auxiliary transistor (6) and the upper resistor (7), and (18) is the second detecting means composed of the lower auxiliary transistor (9) and the lower resistor (10). FIG. 4 is a diagram showing in detail one phase portion of the inverter section shown in FIG. 3, and the same reference numerals as those in FIG. 3 denote the same parts, and therefore the description thereof will be omitted. In the figure, (20a) is a first comparator that compares the voltage drop across the upper resistor (7) with a reference voltage, and (20b) is the voltage drop across the lower resistor (10) as a reference. A second comparator (21) for comparing with the voltage is a cut-off signal output when the voltage drop exceeds the reference voltage in the first and second comparators (20a) (20b). The comparing means (15) is composed of the first and second comparators (20a),
(20b) It consists of three phases.

Next, the operation will be described. In FIG. 3 or 4, when the upper main transistor (5) is in a conducting state and a main current is flowing through the upper main transistor (5), a small capacitance connected in parallel to the upper main transistor (5). The upper auxiliary transistor (6) of the
A minute current shunted at the rate of N flows. When this minute current flows into the upper resistor (7) connected to the upper auxiliary transistor (6), a voltage drop occurs across the upper resistor (7). The current flowing through the upper auxiliary transistor (6) of the first detecting means (17) is proportional to the main current flowing through the upper main transistor (5), and the voltage drop generated in the upper resistor (7) is also proportional to the main current. Have a relationship. Therefore, by comparing the voltage drop generated in the upper resistor (7) with the reference voltage output from the reference voltage generating means (16) by the first comparator (20a), it indirectly flows to the upper main transistor (5). It can be detected that the main current exceeds the reference value.

Then, the first comparator (20a) detects that the main current exceeds the reference value, and the control circuit (1
4), and as a result, the control circuit (14) cuts off the gate signals of the upper and lower main transistors (5) and (8), so that the upper and lower main transistors (5) and (8) are removed from the overcurrent. Protect.

[Problems to be Solved by the Invention]

Since the conventional overcurrent protection device for the inverter device is configured as described above, in order to protect the upper main transistor (5) and the lower main transistor (8) from overcurrent,
It is necessary to detect all the currents flowing in the upper main transistor (5) and the lower main transistor (8) respectively, and there is a problem to be solved such that the circuit is complicated and expensive.

The present invention has been made to solve the above problems, and an object thereof is to obtain an overcurrent protection device for an inverter device, which has a simple circuit configuration and is inexpensive.

[Means for Solving the Problems]

An overcurrent protection device for an inverter device according to the present invention comprises a pair of switching elements connected in series, a plurality of pairs being connected in parallel between an anode and a cathode of a DC power supply, and the respective connection points between the switching elements being output terminals. In the inverter unit for converting direct current into alternating current, detecting means for individually detecting a current flowing in the switching element connected to the cathode side, reference signal generating means for outputting a reference signal of a predetermined level, and Comparing means for individually comparing the respective output signals of the detecting means based on the reference signal and two adjacent signals of the output signals of the detecting means are respectively added, and
The second comparison means for individually comparing the added signals on the basis of the reference signal and the comparison result of the first comparison means or the second comparison means when the comparison result exceeds the reference signal. And a control means for stopping the operation of each switching element.

[Work]

In the present invention, the comparing means determines the overcurrent state of the switching element connected to the cathode side of the DC power source, and the adding means determines the overcurrent state of the switching element connected to the anode side of the DC power source. , And outputs a cutoff signal of the switching element to the control means.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. In the following drawings, the same reference numerals as those in FIGS. 3 and 4 showing the conventional example indicate the same or corresponding portions, and therefore the explanation thereof will be omitted. In FIG. 1, (30) is a comparator corresponding to the first comparing means for comparing the voltage drop occurring in the lower resistor (10) with the reference voltage, and (31) is 2 of the adjacent detecting means (18). It is a second comparing means for adding signals and comparing with a reference voltage. Figure 2 shows the second
FIG. 4 is a diagram showing the comparison means (31) in more detail, in which (40) is a first adder for adding the voltage drops of the U and V phases, and (41) is the voltage drop of the V and W phases. Is added to the second adder, (42) is added to the voltage drop of the W and U phases and added to the third adder, and (43) is compared with the output of the first adder (40) and the reference voltage. A first comparator (44), a second comparator (44) for comparing the output of the second adder (41) with a reference voltage, and (45) an output of the third adder (42) for reference It is a 3rd comparator which compares with a voltage.

Next, the operation will be described. First, the protection of one of the lower main transistors (8) when an overcurrent flows will be described. For example, the lower main transistor (8) of the U phase of the lower main transistor (8)
It is assumed that an overcurrent state has occurred in the. Here, when one lower main transistor (8) is conductive and one or two upper main transistors (5) are conductive, the lower main transistor (8) has the upper main transistor (5). Since a current that flows in one or two flows in, it suffices to detect this current value. Therefore, when an overcurrent state occurs in the U-phase lower main transistor (8) of the lower main transistors (8), the current flowing into the U-phase lower main transistor (8) is provided in parallel with it. The lower auxiliary transistor (9) shunts the current to 1: N, and the voltage drop caused in the lower resistor (10) by this shunt current is compared with the reference voltage by the U-phase comparator (30). When the comparison result exceeds the reference voltage, the U-phase comparator (30) outputs a cutoff signal to the control circuit (14). In response to this signal, the control circuit (14) cuts off the switching operation of the upper and lower main transistors (5) and (8) and protects the U-phase lower main transistor (8) from overcurrent. The same protection operation as above is performed for the other V-phase and W-phase lower main transistors (8).

Next, the protection operation of each of the upper main transistors (5) when an overcurrent flows in one of them will be described. For example, U of the upper main transistor (5)
It is assumed that an overcurrent condition has occurred in the upper main transistor (5) of the phase. Here, when two lower main transistors (8) are conducting and one upper main transistor (5) is conducting, the current flowing through the upper main transistor (5) is lower than the lower main transistor (8) 2. Since the current is divided into individual pieces, it is only necessary to detect the combined value of the divided currents. Therefore, when an overcurrent state occurs in the U-phase upper main transistor (5) of the upper main transistors (5), the current flows out from the U-phase upper main transistor (5) and the V-phase and W-phase lower main transistors (5). The current flowing into the transistor (8) is shunted to 1: N by the lower auxiliary transistor (9) provided in parallel with them, and the voltage drop generated in each lower resistor (10) by these shunt currents is Input to the second comparison means (31). These signals are used as v, w signals in the second adder (4
In 1), the adding operation is executed, and the added value is input to the second comparator (44) and compared with the reference voltage. When the comparison result exceeds the reference voltage, the second comparator (44) outputs a cutoff signal to the control circuit (14). After that,
The control circuit (14) executes the protection operation by the same operation as described above. The same protection operation as above is performed for the other V-phase and W-phase upper main transistors (5).

〔The invention's effect〕

As described above, according to the present invention, the overcurrent of the switching element connected to the cathode side of the DC power supply is detected, and not only the switching element but also the switching element connected to the anode side of the DC power supply is overloaded. Since it is configured so as to be protected from an electric current, there is an effect that a simple and inexpensive circuit configuration can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an overcurrent protection device for an inverter device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing details of adding means according to an embodiment of the present invention, and FIG. 3 is a conventional inverter. FIG. 4 is a circuit diagram showing an overcurrent protection device of the device, and FIG. 4 is a diagram showing in detail one phase of the conventional overcurrent protection device of the inverter device. In the figure, (1) is a converter section, (3) is an anode side bus, (4) is a cathode side bus, (5) is an upper main transistor, (8) is a lower main transistor, (14) is a control circuit,
(16) is a reference voltage generating means, (18) is a second detecting means,
(30) is a comparator, and (31) is a second comparing means. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A pair of switching elements connected in series are connected in parallel between a plurality of anodes and cathodes of a DC power source, and the respective connection points between the switching elements are used as output terminals to convert DC into AC. In the inverter section, a detecting means for individually detecting a current flowing through the switching element connected to the cathode side, a reference signal generating means for outputting a reference signal of a predetermined level, and the detecting means based on the reference signal. Of the output signals of the detection means and the adjacent two signals of the detection means are respectively added, and the added signals are individually output based on the reference signal. A second comparison means for comparing
Overcurrent of the inverter device, comprising: a control unit that stops the operation of each of the switching elements when the comparison result of the first comparison unit or the second comparison unit exceeds the reference signal. Protective device.