JP3095289B2 - Protection circuit for static induction type self-extinguishing element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device using an electrostatic induction type self-extinguishing element as a switching element, and more particularly to a protection circuit for an electrostatic induction type self-extinguishing element which protects this switching element when an abnormal current flows. .

[0002]

2. Description of the Related Art Japanese Unexamined Patent Application Publication No. 61-185064 discloses a conventional method for protecting a switching device of an inverter device using a self-turn-off device of an electrostatic induction type as a switching device. According to the protection method described in the publication, when an abnormal current flows through a switching element, it detects that the collector voltage exceeds a set value and performs gate voltage control to reduce the gate voltage to a predetermined value. Things.

[0003] Apart from this, an overcurrent protection circuit for detecting an overcurrent of the output current and cutting off the output to protect the output current is generally provided.

[0004] The protection by the gate voltage control requires 2 to 4 μm as the time for detecting the collector voltage of the switching element.
It takes about sec. On the other hand, the time for the overcurrent protection circuit to detect the output overcurrent is 10 times due to the delay of the current detector.
About μsec is required.

The value determined as the abnormal current level in the protection method by the gate voltage control is higher than the value determined as the overcurrent level by the overcurrent protection circuit.

A conventional protection operation of an inverter device having such a protection circuit and its problems will be described.

[0007] It is assumed that an abnormal current flows through two switching elements due to a short circuit accident in the inverter device. Generally, when an excessive current flows as in a short circuit accident, the collector voltage of the switching element rises. This allows
First, the protection circuit based on gate voltage control provided for each switching element operates faster than the overcurrent protection circuit.

The protection circuit based on the gate voltage control has the
One of the gate voltage control circuits provided in the two switching elements starts decreasing the gate voltage first due to variations in the collector voltage value of the switching element and the detection time of the gate voltage control circuit. However, in some cases, the abnormal current converges on the other element before the gate voltage control circuit operates, and the collector voltage does not rise above the abnormal current level. In this case, the other element remains in a normal conducting state. Therefore, a large current continues to flow as a return current to the other switching element and the flywheel diode where the gate voltage control circuit is not operating due to the inductance of the wiring up to the short-circuit fault point.

FIG. 6 and FIG. 7 are circuits for explaining the return current. When the short-circuit switching elements TU and TZ are in the ON state, when the gate voltage control circuit of the TU operates for the first time, the abnormal current starts to converge so as to be small. When the abnormal current decreases and the collector voltage falls below the set value Vs, T
Z is particularly slow in collector voltage detection time compared to TU,
There is a case where the gate voltage control circuit enters a normal ON state without operating. In particular, when the short-circuit current is large, the energy stored in the inductance of the wiring keeps flowing the return current to the TZ and the flywheel diode DU which are in the normal ON state.

As shown in FIG. 7, the current of the switching element TU is suppressed by the gate voltage control so as to be small. However, the current of the switching element TZ is larger than the return current by the return current as shown by the diagonal line. Remains.

At this time, an overcurrent protection circuit in which the overcurrent detection level is lower than the abnormal current detection level and which is slower than the protection operation of the gate voltage control detects the return current, and abrupt output cutoff occurs (protection by gate voltage control). The operation suppresses the current to a predetermined value or less, whereas the protection operation by the overcurrent protection circuit operates at a high speed so as to completely shut off the output current, so that the current is rapidly cut off.) In particular, the return current is not more than the abnormal current level, but is not less than the value set as the overcurrent level by the overcurrent protection circuit, and is cut off at high speed. Therefore, there is a risk that a high jump voltage is applied to the switching element and the element is destroyed. is there.

As described above, since there are two overcurrent protection circuits, the protection circuit based on the gate voltage control operates first, and then the overcurrent protection circuit operates to cause the above problem.

[0013]

As described above, in the prior art, there are cases where the gate voltage control protection circuit operates and then the output overcurrent protection circuit operates. In this case, as described above, the electrostatic induction type self-extinguishing circuit is used. A high jump voltage is applied to the collector voltage of the arc element, and the element is destroyed or deteriorated. That is, there is a problem in terms of highly reliable protection at the time of abnormal current.

An object of the present invention is to provide a highly reliable protection circuit so that the above-mentioned problem does not occur when an abnormal current flows, such as when a short circuit occurs.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inverter device using an electrostatic induction type self-extinguishing element as a switching element, in which an overcurrent protection circuit does not shut off an output when a gate voltage control circuit is operating. This is achieved by configuring the protection circuit as described above.

[0016]

The output cutoff prohibition circuit of the inverter device prohibits the output cutoff by the overcurrent protection circuit when the gate voltage control circuit is operating.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.

Reference numeral 1 denotes a forward converter for converting three-phase alternating current to direct current, and RST denotes a power input terminal thereof. Reference numeral 3 denotes a capacitor for smoothing a ripple included in the converted DC, reference numeral 2 denotes an inverse converter for converting the smoothed DC to an AC having an arbitrary voltage and frequency, and UVW is an output terminal thereof. A load is connected to the output terminal UVW. The inverter 2 uses an insulated gate bipolar transistor (hereinafter, referred to as an IGBT), which is an electrostatic induction type self-extinguishing element, as a switching element. Reference numerals 6u and 6w denote U-phase and W-phase current detectors, and 6 is used to stop the operation of the inverter 2 when the detection signals of the current detectors 6u and 6w are input and the set value of the overcurrent level is exceeded. Overcurrent detection circuit that outputs the signal S3 of FIG. Reference numeral 5 denotes a drive signal S8 for driving the switching element by the drive signal S7 in a normal state, and a drive signal in an abnormal state where the drive signal S7 is in an ON signal state and the IGBT collector voltage signal S9 exceeds a set value. This is a gate voltage control circuit that lowers the ON signal voltage of S8 to a predetermined value. 7 is a gate voltage control circuit 5
Receives the signal S2 output during the operation of reducing the ON signal voltage of the drive signal S8 to a predetermined value in an abnormal state, and outputs the output cutoff signal S5 based on the signal S3 from the overcurrent protection circuit 6. This is an output cutoff signal prohibition circuit that prohibits output. Reference numeral 4 denotes a delay circuit for delaying a signal for a predetermined time. Reference numeral 9 denotes a microcomputer which is a central processing unit that executes processing of the inverter device. Reference numeral 8 denotes a drive signal transmission circuit, which normally transmits a drive signal S6 (on / off signal) from the microcomputer 9, and outputs an output cutoff signal S from the output cutoff signal prohibition circuit 7 during overcurrent protection operation.
5 transmits the OFF signal to all the switching elements of the inverter 2 (the ON signal is inhibited).

Next, the present invention will be described in detail. When an element with a high switching speed, such as an IGBT, suddenly cuts off an excessive current as in the case of a short circuit fault, the DC voltage section
A high jump voltage is generated due to the inductance of the wiring leading to the BT. When a high voltage accompanied by the jump is applied to the device, there is a problem in reliability. However, according to the present embodiment, the gate voltage control circuit gradually reduces the gate voltage at the time of short circuit, thereby reducing the current change rate di / dt of the short circuit current and suppressing the jump voltage.

FIG. 2 shows the gate voltage, collector current, and collector voltage characteristics of the IGBT. It can be seen that the collector current can be reduced when the gate voltage is reduced. It can also be seen that the collector voltage increases as the collector current increases when the gate voltage is constant.

FIG. 3 shows a time chart of the gate voltage and the collector current. The solid line is an operation waveform when the gate voltage control circuit according to the present invention operates and the output cutoff operation of the overcurrent protection circuit is prohibited for a predetermined time. The broken line shows the case where the conventional overcurrent protection circuit operates and the output is forcibly cut off. According to this embodiment, the output is not cut off until the collector current becomes sufficiently smaller than the maximum value of the abnormal current.

FIG. 4 shows one switching element (here, U
A block diagram of a gate voltage control circuit per phase) is shown.
The operation of the gate voltage control circuit will be described in more detail with reference to FIG. The gate voltage control circuit 12 operates according to the normal operation drive signal S7 input from the photocoupler PCU.
Pulse voltages VG1 and -VG5 are applied as gate voltages VGE between the gate G and the emitter E of No.5. However, when the drive signal S7 of the IGBT 15 is in the ON state in the event of a short circuit, a large current suddenly flows through the IGBT 15. IG
In the BT 15, the collector voltage also increases as the collector current increases. The collector voltage is input to the comparator 14 and compared with the reference value Vs. When the collector voltage exceeds the reference value Vs, a signal is output to the ON holding circuit 11 and the gate voltage control circuit 12.
The gate voltage control circuit 12 detects the abnormality by inputting the output signal of the comparator 14 only at the time of the ON signal. When the gate voltage control circuit 12 receives from the comparator 14 a signal in which the collector voltage exceeds the set value Vs, the gate voltage control circuit 12 detects the abnormality. Is gradually decreased from VG1.
At this time, in order to perform the gate voltage control for a predetermined time, when the ON holding circuit 11 receives a signal of which the collector voltage exceeds the set value Vs from the comparator 14, the ON state is maintained and the OFF signal is prohibited for a predetermined time. I do. That is, even if the overcurrent protection circuit operates and the drive signal input from the photocoupler PCU is turned off, the operation does not immediately shift to the operation of shutting off the gate. As a result, the circulating current is extended until it becomes sufficiently small. Therefore, even if the overcurrent protection circuit operates, the current change rate di / dt of the collector current is reduced, and the jump voltage is suppressed. At the same time, the abnormal signal is transmitted to the microcomputer 9 as a signal S1 through the photocoupler PCU2, and the microcomputer 9 performs an abnormal display process such as a trip display.

The operation of the gate voltage control circuit 5 to transmit an abnormal signal and inhibit the output cutoff signal will be described with reference to FIG. The drive signal S6 output from the microcomputer 9 is transmitted to the gate voltage control circuit 5 by the photocouplers PCU to PCZ, and the IGBT connected to the output of the gate voltage control circuit 5
Is switched.

When the current of the IGBT is normal and the collector voltage is smaller than the reference value Vs, the gate voltage control circuit 5 is not operating. Everything is off. In this case, the photocouplers PCU2 to PCU
The collector of the output transistor of Z2 is pulled up by the resistor R1, the signal S2 becomes high level H, and the transistor Q2 is turned on. Since the signal S2 is output after inverting the collector voltage of the transistor Q2, the signal S2 has a high level H. At this time, when the signal S3 is output from the overcurrent detection circuit (the signal S3 is at a low level L), the signal S4 is at a low level L, and the signal S5 is at a high level H. As a result, the transistor Q1 is turned off.
All of CU to PCZ are turned off. That is, the output is cut off.

On the other hand, when an abnormal current such that the voltage of the collector exceeds the reference value Vs flows to one of the IGBTs, the corresponding one of the photocouplers PCU2 to PCZ2 is detected by the detection signal of the gate control circuit of each switching element. Is turned on. Therefore, the signal S2 is at the low level L. As a result, the transistor Q2 is turned off after the dead time of the delay circuit 4 composed of the resistors R1, R2, R3 and the capacitors C1, C2, and the signal S1 becomes low level L. When the signal S2 goes low, the signal S4 goes high regardless of the signal S3 from the overcurrent detection circuit 6. Therefore, the signal S5 is initially at the high level H because the signal S1 is at the high level H,
After the delay time of the delay circuit 4, when the signal S1 becomes high level H, it becomes low level L. Correspondingly, transistor Q1 turns off after the dead time of delay circuit 4. The output is cut off by turning off the transistor Q1. As described above, the output cutoff is not related to the signal rising timing of the output signal S3 of the overcurrent detection circuit 6, and the signal S
This is performed when 1 becomes the low level L after the dead time of the delay circuit 4. Since the dead time of the delay circuit 4 is set long enough for the abnormal current to sufficiently attenuate, the output does not shut off when the current value is large. During the operation of the gate voltage control circuit, the output cutoff signal by the overcurrent protection circuit is prohibited, and the return current is not suddenly cut off. Therefore, when an abnormal current flows as in the case of an output short-circuit accident, highly reliable protection can be provided.

[0026]

According to the present invention, when an abnormal current such as a short-circuit fault flows in the inverter device, the output cutoff is prohibited when the gate voltage control circuit is operating, whereby the sudden change from a large current value occurs. No interruption is performed. Therefore, there is an effect that a voltage with a high jump voltage is not applied to the IGBT, and a highly reliable protection circuit can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of an embodiment according to the present invention.

FIG. 2 is a diagram illustrating gate voltage, collector current, and collector voltage characteristics of the IGBT of the present invention.

FIG. 3 is a diagram illustrating a gate voltage and a collector current of the IGBT of the present invention.

FIG. 4 is a block diagram of a gate voltage control circuit according to an embodiment of the present invention.

FIG. 5 is a diagram showing a specific example according to the present invention.

FIG. 6 is a diagram illustrating a return current at the time of a short circuit accident.

FIG. 7 is an explanatory diagram of a short-circuit current including a return current.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Forward converter, 2 ... Inverse converter, 3 ... Smoothing capacitor, 4 ... Delay circuit, 5 ... Gate voltage control circuit, 6 ...
Overcurrent detection circuit, 6u, 6w: current detector, 7: output cutoff signal prohibition circuit, 8: drive signal transmission circuit, 9: microcomputer, PCU-PCZ, PCU2-P
CZ2: photo coupler, Q1, Q2: transistor,
R1, R2, R3: resistor, C1, C2: capacitor.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Kamihara, Inventor 7-1-1 Higashi Narashino, Narashino-shi, Chiba Pref. Narashino Plant, Hitachi, Ltd. (72) Atsuhiko Nakamura 7-1-1, Higashi-Narashino, Narashino-shi, Chiba Hitachi, Ltd. Narashino Plant (72) Inventor Masayuki Hirota 7-1-1, Higashi Narashino, Narashino-shi, Chiba Hitachi Keiyo Engineering Co., Ltd. (56) References JP-A-62-58827 (JP, A) JP-A Sho 61-185064 (JP, A) JP-A-2-50518 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 7/48 H02H 7/122 H02M 1/00 H02M 3 / 00

Claims (1)

(57) [Claims] 1. An electrostatic induction-type self-extinguishing element, a drive circuit for driving the electrostatic induction-type self-extinguishing element, and a predetermined value that detects a current of the electrostatic induction-type self-extinguishing element An overcurrent protection circuit that shuts off the output of the drive circuit when the output voltage exceeds the threshold, and detects the collector voltage of the static induction type self-extinguishing element and detects the electrostatic induction when the detected value exceeds a predetermined value. And a gate voltage control circuit for lowering the gate voltage of the self-extinguishing element, wherein when the gate voltage control circuit controls to reduce the gate voltage, A protection circuit for an electrostatic induction-type self-extinguishing element, further comprising an output cutoff prohibition circuit for prohibiting output cutoff by the overcurrent protection circuit for a predetermined time.