JPH04351113A - Inverter - Google Patents

Abstract

PURPOSE:To realize the inverter whose reliability is improved by disconnecting a failed MOSFET from the circuit in the inverter in which plural field effect transistors(TRs) (MOSFETs) are connected in parallel. CONSTITUTION:The inverter is provided with a control means to which switching elements such as thyristors 10-13 blocking a reverse drain current of MOSFETs 2-5 and conducting a forward drain current are connected in place of reverse blocking diodes connected in series with drains of conventional MOSFETs so as to turn off the switching elements connecting in series with the faulty MOSFETs. The reliability of the inverter is improved by turning off the switching element so as to disconnect the faulty and short-circuited and destroyed MOSFET from the circuit and no current flows to the internal diode of the MOSFET to prevent the destruction due to the internal diode and the destruction due to a surge voltage.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device, and more particularly to an inverter device using field effect transistors.

0002

2. Description of the Related Art Conventionally, a large number of inverter devices have been proposed for inverting the polarity or logic of an output with respect to an input. FIG. 3 is a circuit configuration diagram showing a conventional inverter device. In the figure, 1 is a DC power supply, 2, 3
, 4, 5 are field effect transistors (referred to as MOSFETs), 6, 7, 8, 9 are gate drive circuits that supply gate voltage to MOSFETs 2 to 5, 24, 25, 26, 2
7 is a reverse blocking diode whose cathode is connected to the drain of each of MOSFETs 2 to 5; 18 and 19 are freewheeling diodes; and 20 is an output terminal.

Next, the operation of the above-mentioned conventional inverter device will be explained. Gate drive circuits 6 and 8 are MOSFETs
Supply gate voltage to 2 and 4 at the same timing,
Turn on and off MOSFETs 2 and 4 at the same time, and similarly,
Gate drive circuits 7 and 9 supply gate voltages to MOSFETs 3 and 5 at the same timing to turn on and off MOSFETs 3 and 5 simultaneously. In addition, the gate drive circuit 6
and 7 alternately supply gate voltages to MOSFETs 2 and 3, and similarly, gate drive circuits 8 and 9 supply MOSFETs
Supplying gate voltage alternately to 4 and 5, MOSFE
T2 and 4 are turned on and off as a pair, and MOSFETs 3 and 5 are turned on and off as a pair, so that an AC output voltage is output to the output terminal 20.

MOSFETs have a current balancing effect because their on-resistance exhibits positive temperature characteristics, and therefore a plurality of M
It is possible to operate OSFETs in parallel. In what is shown in FIG. 3, two MOs are used to simplify the explanation.
Although an example in which SFETs are operated in parallel is shown, large-capacity high-frequency inverter devices in which several dozen MOSFETs are operated in parallel have also been realized.

FIG. 4 is an explanatory diagram showing the internal structure of the MOSFET. In the figure, 28 is a gate, 29 is a drain, 30 is a source, and 31 is an internal diode. Due to its structure, the MOSFET shown in FIG. 4 has an internal diode 31 built in equivalently between a drain 29 and a source 30, and this is generally called an internal diode (or built-in diode, body drain diode, etc.). If a reverse voltage is rapidly applied after a freewheeling current flows through the internal diode 31, an excessive recovery current will flow through the internal diode 31, and this excessive recovery current may damage the MOSFET. In the high frequency inverter device that operates,
MOSFE to prevent current from flowing through the internal diode 31.
A reverse blocking diode is connected in series to the drain 29 of T.

[0006]

[Problems to be Solved by the Invention] The conventional inverter device described above is constructed as described above, and the MOSFET
When the MOSFET fails, the drain and source of the MOSFET are usually short-circuited and destroyed, so as shown in Figure 3, the MOSFET
In an inverter device in which multiple SFETs are connected in parallel, even if only one MOSFET fails, this MOSFET
Since a short circuit occurs in the SFET part, normal operation becomes impossible and the inverter device is stopped. Therefore, the failure rate of an inverter device is the number of MOSFETs used multiplied by the failure rate of one MOSFET, and as a result, the more MOSFETs are connected in parallel, the more the failure rate increases. become. As described above, although MOSFETs have characteristics suitable for parallel connection, they have the disadvantage that the failure rate is short-circuit destruction, so when they are connected in parallel, the failure rate of the entire device increases.

[0007] As a means to eliminate this drawback, it is possible to connect a fuse, switch, etc. in series to each MOSFET, and open the fuse or switch only for the MOSFET that has failed and shorted, thereby disconnecting the failed MOSFET from the circuit. It is being However, when fuses, switches, etc. are added to the circuit configuration of a conventional inverter device as shown in FIG. 3 in order to reduce the failure rate, the configuration of the device becomes complicated and costs increase. However, as the wiring becomes longer, the inductance component of the circuit increases, and especially when high frequency switching operation is performed, a surge voltage is generated and the MOSFET is destroyed due to overvoltage.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide an inverter device that can disconnect a failed MOSFET from a circuit without increasing surge voltage.

[0009]

[Means for Solving the Problems] An inverter device according to the present invention includes a switching element that blocks a reverse drain current of a MOSFET and conducts a forward drain current.
connected in series to the drains of each of the plurality of MOSFETs,
A control means is provided to turn off the switching element connected in series to the failed MOSFET.
This is to separate T from the circuit.

0010

[Operation] The inverter device according to the present invention connects a switching element in series to the drain of each of a plurality of MOSFETs, and controls to turn off the switching element connected in series to a failed MOSFET, thereby causing failure and short-circuit damage. The MOSFET that has been removed is disconnected from the circuit,
The inverter device continues to operate using the remaining normal MOSFETs. In addition, the switching element is MOSFE.
By connecting in series to the drain of T, MOSFET
The current flowing through the internal diode is blocked, and the reverse blocking diode in this type of conventional device can be omitted.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an inverter device according to an embodiment of the present invention. In the figure, 1 is a DC power supply, 2
, 3, 4, 5 are field effect transistors (MOSFET)
, 6, 7, 8, and 9 are gate drive circuits that supply gate voltage to MOSFETs 2 to 5, 10, 11, 12, and 13 are thyristors, 14, 15, 15, and 17 are thyristor gate circuits, and 18 and 19 are for free circulation. Diode 20 is an output terminal.

Next, the operation of the inverter device according to the embodiment of the present invention will be explained. The thyristor gate circuits 14 to 17 supply gate signals that always make the thyristors 10 to 13 conductive when the MOSFETs 2 to 5 are not in failure. Here, even when the gate signal is supplied to the thyristor, the reverse current of the thyristor is blocked like a diode, so no current flows to the internal diode of the MOSFET, and the destruction of the internal diode occurs as shown in Figure 3 above. Similar to the conventional device shown, this does not occur. In addition, since a thyristor with almost the same current and voltage capacity as the reverse blocking diode of the conventional device described above can be used, the external shape of the thyristor used is almost the same as that of the reverse blocking diode of the conventional device, so the wiring inductance is lower than that of the conventional device. The surge voltage will not increase as usual. Therefore, the inverter device of this embodiment is capable of high frequency switching operation similar to the conventional device shown in FIG.

Next, when one MOSFET 2 among the MOSFETs 2 to 5 fails, the output of the gate signal of the thyristor gate circuit 14 is stopped and the thyristor 10 is turned off. When the thyristor 10 turns off, MOSFET 2, which has failed due to a short circuit between the drain and source, is disconnected from the circuit, so the remaining normal MOSFET 3
~5, the inverter device continues to operate.

By the way, as a means for detecting a failure in the MOSFET 2 and stopping the thyristor gate circuit 14 of the corresponding thyristor 10, for example, after a failure occurs, the failure of the MOSFET 2 is checked using a measuring instrument such as a tester, and the thyristor gate circuit 14 is manually shut down. There are a method of outputting a signal to stop the circuit 14, a method of providing a failure detection circuit for the MOSFET 2 to automatically detect a failure, and stopping the thyristor gate circuit 14.

FIG. 2 shows the MO in the inverter device of FIG.
FIG. 3 is a circuit configuration diagram showing a failure detection means of SFET. In the figure, 2 is a MOSFET, 6 is a gate drive circuit that supplies gate voltage to MOSFET 2, 10 is a thyristor,
14 is a thyristor gate circuit, 21, 22 are photocouplers, and 23 is an OR gate.

Next, the operation of the MOSFET failure detection means will be explained. Gate drive circuit 6 is MOSFE
Since positive and negative voltages of about 10V are supplied between the gate and source of T2, when MOSFET2 is normal, the logic outputs of photocoupler 21 and photocoupler 22 are "1".
”, “0” are alternately output, and the OR gate 23
The logic output of always outputs "1" to operate the thyristor gate circuit 14. Next, when the MOSFET 2 fails, the insulating oxide film on the gate of the MOSFET 2 is destroyed, the gate and source become short-circuited, and the output voltage of the gate drive circuit 6 drops to about 0V. In this state, the logic outputs of photocouplers 21 and 22 become "0",
The logic output of the OR gate 23 becomes "0", the thyristor gate circuit 14 stops, and the thyristor 10 is automatically turned off.

In addition, when a MOSFET fails, the drain and gate are also short-circuited, so the drain voltage,
There is also a means of detecting the gate voltage using a photocoupler or the like. Additionally, there are mechanisms for detecting the case temperature and radiation fin temperature of a MOSFET, and mechanisms for detecting overcurrent provided with a MOSFET drain current detection means.

[0018] In the above embodiment, the case where a thyristor was used as the switching element was explained, but the GT
O (gate turn-off thyristor) may be used.

Furthermore, in the above embodiment, an inverter device in which two MOSFETs are connected in parallel has been described.
An inverter device in which two or more SFETs are connected in parallel may also be used.

Furthermore, in the above embodiment, an inverter device composed of one arm has been described, but an inverter device composed of a plurality of arms may be used.

[0021]

As described above, according to the inverter device of the present invention, the switching element that blocks the reverse drain current of the MOSFET and conducts the forward drain current is connected in series with the drain of each of the plurality of MOSFETs. Since the configuration is equipped with a control means to turn off the switching element connected in series to the failed MOSFET, the failed MOSFET can be disconnected from the circuit and
The remaining normal MOSFETs allow the inverter device to continue operating, extending the operating time of the device, and blocking the current flowing to the internal diodes of the MOSFETs, making them ideal for reverse blocking. Diode can be omitted, damage caused by internal diode,
This provides an excellent effect of providing an inverter device that has high reliability without being destroyed by surge voltage and is capable of high frequency switching operation.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an inverter device that is an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram showing a MOSFET failure detection means in the inverter device of FIG. 1;

FIG. 3 is a circuit configuration diagram showing a conventional inverter device.

FIG. 4 is an explanatory diagram showing the internal configuration of a MOSFET.

[Explanation of symbols]

1 DC power supply 2, 3, 4, 5 Field effect transistor (MOS
FET) 6, 7, 8, 9 Gate drive circuit 10, 11, 1
2, 13 Thyristor 14, 15, 16, 17
Thyristor gate circuit 18, 19 Freewheeling diode 20 Output terminal 21, 22 Photocoupler 23 OR gate 24, 25, 26, 27 Reverse blocking diode 2
8 Gate 29 Drain 30 Source 31 Internal diode

Claims (1)

[Claims] 1. An inverter device configured by connecting in parallel at least two field effect transistors connected in series and controlled to turn on and off alternately, wherein the field effect transistors are connected in series to the drains of each of the field effect transistors. and comprising a switching element that blocks a reverse drain current of the field effect transistor and conducts a forward drain current, and a control means that turns off the switching element connected in series to the failed field effect transistor. Features of the inverter device.