JP2002095151A - Overcurrent protecting circuit of igbt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent breakdown due to overcurrent or overvoltage, and enable safe transition to the off-state, when an overcurrent flows in an IGBT. SOLUTION: When a state of overcurent is generated, a gate voltage of the IGBT is decreased quickly as far as a set value by a gate current increasing means, and switching operation is started quickly. After that, the gate voltage holds the set value, and gentle switching is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an IGBT overcurrent protection circuit.

[0002]

2. Description of the Related Art Insulated gate bipolar transistors (Ins)
A ulated gate bipolar transistor (IGBT) is widely used in inverter circuits and the like because it has a high withstand voltage and can switch a large current at high speed. An abnormal situation in these inverter circuits is as follows.
There is a so-called short-circuit accident that is short-circuited by the GBT and an excessive current flows through the IGBT. It is desired that the IGBT interrupts the short-circuit current without breaking even during the short circuit. Therefore, an overcurrent protection circuit that detects an overcurrent of the IGBT and turns off the IGBT at the time of the overcurrent is widely used. The current reduction rate di / dt at this time is IGBT
Has a very large value because it has high-speed switching characteristics. Therefore, the jump voltage Ldi / dt due to the wiring inductance L becomes very large, and the IGBT
However, there is a problem that overvoltage is destroyed.

[0003] As a conventional technique for solving this problem, there is Japanese Patent No. 2889215 and the like. This prior art is to reduce the gate voltage of the IGBT step by step when the overcurrent is cut off. This realizes gradual switching,
Di / dt at the time of overcurrent interruption is reduced to prevent overvoltage destruction.

[0004]

In the conventional inverter circuit, a snubber circuit is usually provided in parallel with the IGBT to perform functions such as overvoltage protection. In recent years, however, snubberless inverters without a snubber circuit have been increasing for miniaturization and cost reduction. Snubberless inverters are designed to minimize wiring inductance to minimize overvoltage. However, since the inductance of the wiring has a function of suppressing the current rise rate di / dt when an overcurrent occurs, the snubberless inverter has a very large di / dt. Therefore, the current of the IGBT rises in a short time, and a gradual switching as in the above-described conventional technique causes a new problem that an overcurrent is destroyed before the transition to the cutoff operation.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to prevent an IGBT from being damaged by overvoltage by suppressing the overcurrent when an overcurrent occurs and suppressing the current reduction rate di / dt at the time of interruption.

[0006]

In the overcurrent protection circuit according to the present invention for solving the above-mentioned problems, when the IGBT enters an overcurrent state, first, the gate voltage of the IGBT is reduced to a set value by a gate current increasing means to perform a switching operation. To start immediately. Thereafter, the gate voltage is maintained at the set value, and relatively gradual switching is realized, and di / dt at the time of cutoff is suppressed to prevent overvoltage breakdown.

[0007]

FIG. 1 is a block diagram showing an overcurrent protection circuit of an IGBT according to a first embodiment of the present invention. The drive circuit 13 uses the signal input from the input terminal T1 to
Turn on / off the BT. The overcurrent detection circuit 11 is an IGBT
Outputs an overcurrent detection signal when is in an overcurrent state. The gate voltage holding means 14 holds the gate voltage of the IGBT at a set value when an overcurrent is detected. Further, the gate current increasing means 15 temporarily increases the gate current of the IGBT so that the gate voltage quickly reaches the set value after the output of the overcurrent detection signal.

Here, the set value of the gate voltage is substantially equal to the gate threshold voltage of the IGBT. Therefore, immediately after the occurrence of the overcurrent, the gate voltage of the IGBT becomes about the threshold value, and the switching is started immediately. Therefore, the IGBT is prevented from being destroyed due to the overcurrent. Then IG
Since the gate voltage of the BT keeps the threshold value, the IGBT shifts to the off state at a gentle current decrease rate di / dt. As a result, overvoltage due to wiring inductance is suppressed, and overvoltage breakdown of the IGBT is prevented. Delay circuit 1
2 operates the gate drive circuit after a predetermined time has elapsed after the occurrence of the overcurrent to shift the IGBT to the stable off state. At this time, the delay time of the delay circuit is set by the gate voltage control means 20 to a time at which the current of the IGBT becomes equal to or less than the normal conduction current, thereby preventing the IGBT from being destroyed.

FIG. 2 shows a specific circuit example of the embodiment of FIG. 1 of the present invention. FIG. 3 shows a protection operation waveform at the time of overcurrent in the embodiment of FIG. The solid line in the figure shows the operation waveform of the overcurrent protection circuit of the embodiment, and the dotted line shows the operation waveform of the conventional protection circuit. The IGBT is driven by an on / off signal input to the input terminal T1. When the on / off signal goes high, the transistor Q3 turns on and the transistor Q3
2 turns on. Then, a current flows through the gate of the IGBT through the resistor R3, and the gate voltage drops to 0 V, and the IGBT is turned off. Conversely, when the on / off signal goes low, the transistor Q3 turns off and the transistor Q1 turns on. Then, a current flows through the gate of the IGBT via the resistor R2, and the gate voltage rises to the power supply voltage E1 to be turned on.

Here, it is assumed that the IGBT is turned on at time t1, and the overcurrent state is left as it is. The overcurrent detection circuit 11 determines that the IGBT is in an overcurrent state, and
2 outputs an overcurrent detection signal. The transistor Q4 is turned on by the overcurrent signal. At this time, since the capacitor C1 is not charged, the transistors Q1, Q
The gate voltage of No. 2 drops sharply from the power supply voltage E1. As a result, the transistor Q2 is turned on, and a large gate current flows through the IGBT. Thereafter, the capacitor C1 is connected to the resistor R4.
Is gradually charged by the current passing through. Accordingly, the gate voltages of Q1 and Q2 rise again, and the gate current of the IGBT decreases. The gate voltages of Q1 and Q2 are constant at a voltage determined by the ratio of the resistance values of R4 and R5, and the gate voltage of the IGBT is also constant at this value Vset.

Here, the ratio of the resistors R4 and R5 is Vset
Are set to substantially match the threshold voltage of the IGBT. The capacity of C1 and the time constant of charging are set so that the gate voltage of the IGBT decreases to near the threshold value when C1 is charged.

For this reason, the gate voltage of the IGBT immediately drops to near Vset after the occurrence of the overcurrent. Therefore, IGB
Switching starts immediately before a large overcurrent of T flows and breaks. Thereafter, the gate voltage of the IGBT becomes Vse
In order to maintain the time t, the IGBT has a gentle current decrease rate di.
The transition to the off state occurs at / dt. As a result, overvoltage due to wiring inductance is suppressed, and overvoltage breakdown of the IGBT is prevented.

Thereafter, at time t3, the delay circuit 12 outputs an overcurrent signal to the OR circuit 16. As a result, the gate voltage of the IGBT is reduced to 0 V by the same operation as in the normal off state, and the IGBT shifts to a stable off state. At this time, the delay time of the delay circuit is adjusted by the gate voltage control means 20 to IG.
The time when the current of the BT becomes equal to or less than the normal conduction current is set to prevent the IGBT from being broken.

FIG. 4 shows an IGB according to a second embodiment of the present invention.
FIG. 2 shows a block diagram of a T overcurrent protection circuit. Drive circuit 13
Turns on / off the IGBT by a signal input from the input terminal T1. The overcurrent detection circuit 11 outputs an overcurrent detection signal when the IGBT enters an overcurrent state. The gate voltage holding means 14 holds the gate voltage of the IGBT at a set value when an overcurrent is detected. After the overcurrent detection signal, the gate current increasing means 15 temporarily increases the gate current of the IGBT so as to quickly approach the set value. Further, the gate current suppressing means 17 suppresses the gate current after the gate current increasing means 15 operates, and suppresses the gate current so that the gate voltage gradually decreases to the set value.

Here, the set value of the gate voltage is set to be substantially equal to the lower limit value in consideration of the fact that the threshold voltage of the IGBT varies depending on the element. Further, the gate voltage immediately after the gate current increasing means operates is set to be the upper limit value of the variation of the threshold voltage.

Therefore, immediately after the occurrence of the overcurrent, the IGB
The gate voltage of T becomes about the upper limit of the threshold value, and then the IGBT starts switching immediately. Therefore, the IGBT is prevented from being destroyed due to the overcurrent. Then IG
The gate voltage of the BT is increased by the action of the gate current suppressing means.
It gradually decreases to the lower limit value of the threshold voltage. Therefore, even in the case of an IGBT having a different threshold, the gate voltage always drops to the threshold voltage or less during this period, and the IGBT shifts to the off state at a gentle current decrease rate di / dt. As a result, overvoltage due to wiring inductance is suppressed, and overvoltage breakdown of the IGBT is prevented. As a result, it is possible to safely protect an IGBT having a variation in characteristics with the same protection circuit. The delay circuit 12 operates the gate drive circuit after a lapse of a predetermined time after the occurrence of the overcurrent to shift the IGBT to a stable off state. At this time, the delay time of the delay circuit is set by the gate voltage control means 20 to a time at which the current of the IGBT becomes equal to or less than the normal conduction current, thereby preventing the IGBT from being destroyed.

FIG. 5 shows a specific circuit example of the embodiment of FIG. 4 of the present invention. FIG. 6 shows a protection operation waveform at the time of overcurrent in the embodiment of FIG. The solid line in the figure shows the operation waveform of the overcurrent protection circuit of the present invention, and the dotted line shows the operation waveform of the conventional protection circuit. The IGBT is driven by an on / off signal input to the input terminal T1. When the on / off signal goes high, the transistor Q3 turns on and the transistor Q3
2 turns on. Then, a current flows through the gate of the IGBT through the resistor R3, and the gate voltage drops to 0 V, and the IGBT is turned off. Conversely, when the on / off signal goes low, the transistor Q3 turns off and the transistor Q1 turns on. Then, a current flows through the gate of the IGBT via the resistor R2, and the gate voltage rises to the power supply voltage E1 to be turned on.

Here, it is assumed that the IGBT is turned on at time t1 and the overcurrent state is left as it is. The overcurrent detection circuit 11 determines that the IGBT is in an overcurrent state, and
2 outputs an overcurrent detection signal. The transistor Q4 is turned on by the overcurrent signal. At this time, since the capacitor C1 is not charged, the transistors Q1, Q
The gate voltage of No. 2 drops sharply from the power supply voltage E1. As a result, the transistor Q2 is turned on, and a large gate current flows through the IGBT. Thereafter, the capacitor C1 is connected to the resistor R4.
Is gradually charged by the current passing through. Accordingly, the gate voltages of transistors Q1 and Q2 rise again, and IG
The gate current of the BT decreases.

The capacitor C2 is charged up to the power supply voltage E1 when an overcurrent occurs. When the transistor Q4 turns on, the capacitor C2 discharges through the resistor R6 and the transistor Q2. At this time, the time constant of the discharge is determined by the capacitor C1.
Set it slower than the charging speed of. As a result, after a large gate current flows through the capacitor C1, the gate voltages of the transistors Q1 and Q2 gradually decrease with the discharge of the capacitor C2. Thereafter, when the capacitor C2 is discharged, the gate voltages of the transistors Q1 and Q2 become
It becomes constant at a voltage determined by the ratio of the resistance values of the resistors R4, R5, R6 and R7, and the gate voltage of the IGBT also becomes equal to this value Vse
It becomes constant at t.

Here, the ratio of the resistors R4, R5, R6 and R7 is set to the lower limit value of Vset in consideration of the fact that the threshold value of the IGBT varies depending on the element. The gate voltage after a large current flows through the gate by the capacitor C1 is set to be the upper limit value of the variation in the threshold value of the IGBT.

Therefore, immediately after the occurrence of the overcurrent, the IGB
The gate voltage of T becomes about the upper limit of the threshold value, and then the IGBT starts switching immediately. Therefore, the IGBT is prevented from being destroyed due to the overcurrent. Then IG
The gate voltage of the BT gradually decreases to the lower limit of the threshold voltage as the capacitor C2 discharges. Therefore, even in the case of an IGBT having a different threshold, the gate voltage always drops to the threshold voltage or less during this period, and the IGBT shifts to the off state at a gentle current decrease rate di / dt. As a result, overvoltage due to wiring inductance is suppressed, and overvoltage breakdown of the IGBT is prevented. As a result, it is possible to safely protect an IGBT having a variation in characteristics with the same protection circuit.

Thereafter, at time t3, the delay circuit 12 outputs an overcurrent signal to the OR circuit 13. As a result, the gate voltage of the IGBT is reduced to 0 V by the same operation as in the normal off state, and the IGBT shifts to a stable off state. At this time, the delay time of the delay circuit is adjusted by the gate voltage control means 20 to IG.
The time when the current of the BT becomes equal to or less than the normal conduction current is set to prevent the IGBT from being broken.

FIG. 7 shows an IGB according to a third embodiment of the present invention.
FIG. 4 shows a block diagram of a T gate drive circuit. The overcurrent detection circuit 11 outputs a detection signal when the IGBT current becomes an overcurrent. The signal generator 32 receives the overcurrent detection signal or the on / off signal from the input terminal T1, and outputs a gate current command signal. The constant current source 31 supplies a gate current according to the gate current command signal to the gate of the IGBT. Here, if an overcurrent is detected, the signal generating means 32 outputs a large gate current command until the gate voltage decreases to about the threshold voltage. After that, a small current command is output.

For this reason, the gate voltage of the IGBT immediately drops to the threshold voltage after the occurrence of the overcurrent. This gives I
Switching can be started promptly before a large overcurrent flows through the GBT and destroys it. After that, IGBT
Is small, and the gate voltage becomes substantially constant, so that the IGBT shifts to the off state at a gentle current decrease rate di / dt. As a result, overvoltage due to wiring inductance is suppressed, and IGBT overvoltage destruction is prevented.

FIG. 8 shows an IGB according to a third embodiment of the present invention.
FIG. 2 shows a circuit diagram of a T gate drive circuit. Resistance R12, R1
3, switching elements Q12, Q13, operational amplifier O
A constant current circuit is constituted by 1 and O2. The resistance R
10, R11 and switching elements Q10, Q11 form a constant voltage circuit. The signal creating means 32 gives commands to these constant current sources and constant voltage circuits. The overcurrent detection circuit 11 outputs a detection signal when the IGBT current becomes an overcurrent. When the overcurrent detection signal is output, the signal generating means 32 outputs a gate current command signal to the operational amplifier O2. The operational amplifier O2 drives the switching element Q13 so that a current corresponding to the command signal flows to the gate of the IGBT via R13. Here, the gate current command is set to a large value during a period until the gate voltage decreases to about the threshold voltage, and thereafter, a small current command is output. Thereafter, the signal generating means drives Q11 to keep the IGBT in a stable off state.

For this reason, the gate voltage of the IGBT immediately drops to the threshold voltage after the occurrence of the overcurrent. This allows IG
Switching can be started immediately before a large overcurrent flows through the BT and the BT is destroyed. After that, since the gate current of the IGBT becomes small and the gate voltage becomes almost constant,
The IGBT shifts to the off state at a gentle current decrease rate di / dt. As a result, overvoltage due to wiring inductance is suppressed, and IGBT overvoltage destruction is prevented.

At this time, the gate current is switched by detecting the gate voltage of the IGBT, but may be switched after a predetermined time has elapsed. In the embodiment, the gate current can be arbitrarily controlled not only at the time of overcurrent but also at the time of normal on / off control. Therefore, it is possible to arbitrarily control the current change rate di / dt, the voltage change rate dV / dt, and the jump voltage during normal switching. Normal di /
Suppressing dt, dV / dt, or a jump voltage causes an increase in loss. In the embodiment, however, the increase in loss is minimized because the gate current is suppressed only during a period in which the current or voltage changes.

FIG. 9 is a circuit diagram of a snubberless inverter according to a fourth embodiment of the present invention. Although partially omitted,
The IGBTs U to Z all have the first or second aspect of the present invention.
Of the IGBT overcurrent protection circuit or the third
Is connected. When a short-circuit accident occurs in which IGBTs connected in series, for example, U and X are simultaneously turned on after passing, a current rise rate di / d expressed by a value obtained by dividing the power supply voltage E2 by the wiring inductance L1.
An overcurrent with t = E2 / L1 flows through the IBGT. In a snubberless inverter, usually, the wiring inductance L1
Is much smaller than an inverter with a conventional snubber circuit. Therefore, the current rise rate di / dt becomes very large. However, in this embodiment, switching can be started immediately after the occurrence of the overcurrent, so that destruction due to the overcurrent can be prevented. At the same time, the jump voltage at the time of interruption can be kept low,
Destruction due to overvoltage is also prevented.

[0029]

As described above, according to the present invention, the IGBT can be prevented from being destroyed due to the overcurrent. Further, it is possible to prevent the IGBT from being destroyed due to the jump voltage caused by the wiring inductance. Further, according to the present invention, it is possible to safely protect the IGBT even when the characteristics of the IGBT vary.

[Brief description of the drawings]

FIG. 1 is a block diagram of an IGBT overcurrent protection circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit example of an IGBT overcurrent protection circuit according to the first embodiment of the present invention.

FIG. 3 is an operation waveform of the overcurrent protection circuit of the IGBT according to the first embodiment of the present invention.

FIG. 4 is a block diagram of an IGBT overcurrent protection circuit according to a second embodiment of the present invention.

FIG. 5 is a circuit example of an IGBT overcurrent protection circuit according to a second embodiment of the present invention.

FIG. 6 is an operation waveform of the overcurrent protection circuit of the IGBT according to the second embodiment of the present invention.

FIG. 7 is a block diagram of an IGBT overcurrent protection circuit according to a third embodiment of the present invention.

FIG. 8 is a circuit example of an IGBT overcurrent protection circuit according to a third embodiment of the present invention.

FIG. 9 shows a snubberless inverter according to a fourth embodiment of the present invention.

[Explanation of symbols]

11: overcurrent detection circuit, 12: delay circuit, 13: IGB
T drive circuit, 14 gate voltage holding means, 15 gate current increasing means, 16 OR circuit, 17 gate current suppressing means, 20 gate control circuit at overcurrent, 31 constant current source, 32 signal generation Means, C1, C2 ... capacitor, D
1: Diode, E1, E2: DC power supply, IGBT: I
GBT elements, Q1 to 4, Q10 to 13 switching elements, R1 to 7, R10 to 13 resistance input terminals, TU, T
V, TW: Inverter output terminal, U, V, W, X, Y,
Z: IGBT, Vset: Set voltage, inverter output terminal.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Nagasu 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture F-term in Hitachi Research Laboratory, Hitachi Ltd. 5G004 AA04 AB02 BA03 BA04 BA07 DC03 EA01 5G053 AA01 AA02 AA09 BA01 CA02 EB01 EB02 EC03 5H007 CA01 CB05 CC23 DC02 FA03 5H740 BA11 BB05 BB09 BC01 BC02 JA01 JB01 MM12

Claims (7)

[Claims] A gate drive circuit for driving an IGBT and an IG
An overcurrent protection circuit for an IGBT, comprising: an overcurrent detection circuit for detecting an overcurrent state of the BT; and an overcurrent gate control circuit for controlling a gate voltage of the IGBT when an overcurrent occurs. An IGBT having a gate voltage holding means for holding a gate voltage at a set value and a gate current increasing means for temporarily increasing a gate current in order to quickly shift the gate voltage to the set value.
Overcurrent protection circuit. 2. An overcurrent detecting circuit for driving an IGBT, an overcurrent detecting circuit for detecting an overcurrent state of the IGBT, and an overcurrent gate control circuit for controlling a gate voltage of the IGBT when an overcurrent occurs. In the overcurrent protection circuit of the IGBT, the overcurrent gate control circuit drives the driving switching element, and a resistor connected in series with a switching element that operates by a signal from the overcurrent detection circuit; and An IGBT overcurrent protection circuit having a capacitor connected in parallel with a resistor. 3. A gate drive circuit for driving an IGBT;
An overcurrent protection circuit for an IGBT, comprising: an overcurrent detection circuit that detects an overcurrent state of the GBT; and an overcurrent gate control circuit that controls a gate voltage of the IGBT when an overcurrent occurs. A gate voltage holding means for holding the gate voltage at a set value, a gate current increasing means for temporarily increasing the gate current to quickly reduce the gate voltage, and a gate voltage after the gate voltage increasing means operates. Is an overcurrent protection circuit of an IGBT having a gate current suppressing means for gradually shifting to the set value. 4. A gate drive circuit for driving an IGBT;
An overcurrent protection circuit for an IGBT, comprising: an overcurrent detection circuit that detects an overcurrent state of the GBT; and an overcurrent gate control circuit that controls a gate voltage of the IGBT when an overcurrent occurs. Means for increasing the gate current during the period from the occurrence of an overcurrent to the gate voltage of the IGBT to a predetermined value over the subsequent periods, and after the gate voltage reaches the predetermined value. An overcurrent protection circuit for an IGBT having a gate current suppressing means for suppressing a gate current during a period until the collector voltage of the IGBT does not change any more than in other periods. 5. An overcurrent detection circuit for detecting an overcurrent state of the IGBT, a signal generation means for generating a gate current control signal from an overvoltage detection signal and an external control signal, and a signal generated by the signal generation means. An overcurrent protection circuit for the IGBT, the constant current source supplying current to the gate of the IGBT. 6. The signal generating means according to claim 5, wherein
IGBT that changes the signal according to the gate voltage of GBT
Overcurrent protection circuit. 7. The I according to claim 1, wherein
A snubberless inverter using a GBT overcurrent protection circuit.