JP2015202035A - Gate drive circuit of voltage-driven power semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem of a system for protecting a semiconductor switch device upon occurrence of arm short circuit, by detecting the absolute value of current and determining occurrence of arm short circuit when it exceeds a set value, that since a large current is cut off, there is a great risk of leading to device destruction.SOLUTION: A gate drive circuit for driving a voltage-driven power semiconductor device applied to a power converter is provided with short circuit current detection means for detecting a short circuit current flowing through the power semiconductor device, and short circuit current integration means for integrating the current detection value. When the integration value of the short circuit current integration means goes above a set value, the gate is cut off forcibly.

Description

  The present invention relates to an overcurrent protection system in a gate drive circuit that drives a voltage-driven power semiconductor element such as an IGBT.

  FIG. 5 shows an example of a main circuit diagram of an inverter system using an IGBT as a voltage-driven power semiconductor switching element. Reference numeral 1 denotes a DC power supply circuit (in the case of an AC power supply input, it is composed of a rectifier 1a and a large-capacitance capacitor 1b that receive the AC power supply 1c as input, and the voltage value thereof is taken as Ed). 2 is an inverter circuit composed of an IGBT that converts DC voltage into AC and a diode, 3 is an IGBT gate drive circuit (connected to each element), 4 is an IGBT, 5 is a diode connected in reverse parallel, and 6 is an electric motor. And so on. Here, in the case of a three-phase inverter, the inverter circuit is composed of six arms, but since the configuration is the same for each arm, only one arm is given a component symbol. Reference numeral 7 denotes a control signal (input to each gate drive circuit) for turning on / off the IGBT, which is output from the control circuit 8 to the gate drive circuit of each IGBT.

  FIG. 6 shows a detailed circuit diagram of the gate driving circuit 3 having a function of forcibly blocking when the IGBT becomes overcurrent. 9 is a gate drive power supply of this circuit, 10 and 11 are switch elements such as transistors for turning on and off the IGBT 4, and in this case, the turn-on side 10 is an NPN transistor and the turn-off side 11 is a complementary using a PNP transistor. It is composed of a connection circuit and operates complementarily by a signal 13 via an insulator 12 such as a photocoupler. In the case of this figure, when the signal 13 becomes H (high), the transistor 10 is turned on. As a result, a current flows into the gate of the IGBT 4 and the IGBT 4 is turned on. On the other hand, when the signal 13 is L, the PNP transistor 11 is turned on, so that a current flows in a direction in which the gate charge accumulated in the IGBT 4 is discharged, and the IGBT 4 is turned off. Reference numeral 14 denotes a gate resistor for limiting the on-side gate current, and reference numeral 15 denotes a gate resistor for limiting the off-side gate current. The switching speed is adjusted by the resistance value. Reference numerals 16 (16a and 16b) denote base resistances of the transistors 10 and 11, and reference numerals 17 and 18 denote current bypass diodes during normal operation.

FIG. 9 shows an example of the collector current (I _C ) and the gate-emitter voltage waveform (V _GE ) when the IGBT is turned on during normal operation. In the case of the upper and lower arms, when the gate voltage V _GE rises due to the ON signal command, the collector current Ic has a waveform in which the reverse recovery current 28 of the diode is superimposed on the load current.

  FIG. 7 shows an operation diagram when one of the upper and lower arms of the inverter circuit breaks down due to an arm short circuit failure. When an ON command is input to the IGBT Qu on the opposite arm side of the IGBT Qd that has undergone a short circuit failure, a DC power supply is short-circuited, and an excessive short circuit current (about 5 to 10 times the rated current of the normal IGBT) flows through a path indicated by a broken line. On the other hand, the IGBT has a short-circuit withstand time (generally about 10 μs) and an allowable short-circuit energy, and short-circuit protection is possible if it can be cut off so as to be within the rated current within this time.

  In FIG. 6, a circuit other than that described above is a circuit for implementing short circuit protection, and 21 is a sense IGBT for detecting a current flowing in the IGBT provided in the IGBT chip. In general, current flows in the sense IGBT at a ratio of about 1/1000 with respect to the main IGBT (the exact ratio is set at the time of designing the IGBT chip).

By connecting the resistor 22 in series with the sense IGBT 21 and detecting the voltage 23 generated in the resistor 22, it is possible to indirectly detect the current flowing through the main IGBT 4. Therefore, when the voltage 23 is input to the comparator circuit 25 and compared with the set value of the voltage setting unit 33, if it is equal to or higher than the set value, it is determined that the overcurrent state or the power supply short circuit (arm short circuit) state exists. The IGBT can be protected by forcibly shutting off by turning on the switch circuit 24 via the signal latch SR flip-flop circuit 35. However, since a large current is cut off at this time, it is necessary to perform a soft cut-off operation by a high gate resistance cut-off or a method of gradually reducing the gate-emitter voltage (circuit method of FIG. 6). FIG. 10 shows an example of a waveform diagram of each part when the arm is short-circuited when this circuit is applied. When the NPN transistor 10 is turned off and the PNP transistor 11 is turned on, the IGBT 4 is forcibly cut off. However, since the capacitor 26 is connected at this time, the potential at the point P does not decrease immediately but decreases with a certain time depending on the discharge time constant between the resistor 27 and the capacitor 26. For this reason, a substantially similar waveform is applied to the gate part (V _GE ) of the IGBT, the current change rate (−di / dt) of the collector current interruption is limited during that period, and a software that does not generate a large turn-off surge voltage (V _CEpeak ). Blocking can be achieved. FIG. 10 shows a series of schematic waveforms (collector current I _C , collector-emitter voltage V _CE , gate-emitter voltage V _GE ). When the short-circuit current Ic flows, the voltage V _CE applied to the IGBT is a voltage obtained by subtracting the voltage drop due to the wiring inductance from the DC power supply voltage Ed. Further, when the short circuit current reaches I _Cpeak and the gate signal is cut off, the gate voltage V _GE decreases with a predetermined time constant by the soft cut-off operation. As a result, the current reduction rate (−di / dt) becomes gradual, the voltage increase rate (dv / dt) also becomes gradual, and the surge voltage (V _CEpeak ) applied to the IGBT is suppressed to a low value.

These circuits enable protection from an overcurrent state such as a short circuit between the upper and lower arms of the IGBT.
FIG. 8 shows a method for detecting an overcurrent state other than that shown in FIG. FIG. 8A shows a system in which a shunt resistor SR is connected in series with the IGBT Q1, and FIG. 8B shows a system in which a current detector such as CT is connected in series with the IGBT Q1. Each gate drive circuit GD1, GD2 converts the detection amount from each detector into a voltage corresponding to the current value, and turns on the switch circuit 24 of the circuit in FIG. 6 when this voltage exceeds a predetermined value. It is. Basically, when the detected value is equal to or greater than a certain threshold value, it is determined that the current is in an overcurrent state, and forced shutdown is performed, so that the operation is the same as that in FIG.

  Examples of the gate drive circuit including the overcurrent detection and soft cutoff circuit shown in FIG. 6 are described in Patent Document 1, Patent Document 2, and the like.

JP 2002-27657 A JP 2007-104805 A

As described above, when an arm short-circuit occurs, the IGBT must be shut off within the allowable short-circuit tolerance time and energy tolerance. Therefore, the arm short-circuit state is detected quickly and the surge voltage is reduced when a large current is interrupted. It is necessary to turn off the software.
In order to detect the short-circuit current promptly, the detection value may be lowered. On the other hand, the reverse recovery current of the diode normally generated at the time of turn-on (28 in FIG. 9: characteristics of the IGBT and the diode, and the gate drive condition) (Although it may vary depending on the load current, it may flow about twice the load current instantaneously) is not a short-circuit current, so it must not be detected as an overcurrent, and the detection variation of the current detector must also be taken into account. The actual set value needs to be set at several times the maximum current value of the system.

Furthermore, since a certain amount of time is required for the delay time on the circuit and the extraction of the gate charge charges after the overcurrent is detected until the interruption operation is actually started, the current may continue to increase during that time ( Δt in FIG. Furthermore, since the surge voltage (V _CEpeak ) generated by di / dt at the time of interruption needs to be less than the specified value, it is necessary to cut off in a short time, and soft interruption over time in a trade-off manner. Necessary.
As described above, if the protective interruption at the time of short circuit is not properly performed with a certain margin, the short circuit withstand time, short circuit withstand energy will be exceeded, surge voltage will be excessive, and the element will be destroyed.
Further, the current detection method using the sense IGBT has a current ratio of about 1/1000 to the current of the main IGBT. Therefore, in a transient state such as turn-on or turn-off of the IGBT, the sense IGBT and the current detection resistor unit connected in series A noise having a high frequency component is applied (FIG. 11 shows an example of a current detection signal waveform in which noise is superimposed at the time of turn-on, and the current waveform when the arm is short-circuited is also similar), and the instantaneous current value is accurately measured. There is a problem that cannot be measured easily. Therefore, generally, the time until the turn-on transient is completed (several hundred ns to several μs) is set as the overcurrent non-detection period.

For this phenomenon, if a non-detection period in which no current is detected is extended or a filter circuit with a long time constant is connected, an overcurrent state can be detected accurately, but the IGBT is cut off accordingly. The time to do becomes longer. On the other hand, if the non-detection time is shortened, a trade-off characteristic that the possibility of malfunction detection due to noise is high.
Therefore, an object of the present invention is to provide a method capable of detecting an overcurrent state even during a rising period of a current in which a large noise signal is superimposed in a transient state at the time of switching. It is to provide a high short circuit protection scheme.

  In order to solve the above-described problem, in the first invention, in a gate drive circuit for driving a voltage-driven power semiconductor element applied to a power converter, a short circuit for detecting a short-circuit current flowing in the power semiconductor element. A current detection means and a short-circuit current integration means for integrating the current detection value are provided. When the integration value of the short-circuit current integration means is equal to or greater than a set value, the gate is forcibly cut off.

  In the second invention, in the gate drive circuit of the voltage-driven power semiconductor element in the first invention, the integration range of the short-circuit current integrating means is a set integration time from the time when the voltage-driven power semiconductor element is turned on. Up to.

  In a third aspect of the invention, in the gate drive circuit for a voltage-driven power semiconductor element according to the second aspect of the invention, a set integration time from the turn-on start time is within an allowable short-circuit time of the voltage-driven power semiconductor element. .

  In the fourth invention, the integration start time of the short-circuit current integrating means in the gate drive circuit of the voltage-driven power semiconductor element in the first invention is a set time after the turn-on start time.

  In the fifth invention, the integration end time of the short-circuit current integrating means in the fourth invention is a time when the time from the turn-on start time is within the short-circuit allowable time of the voltage-driven power semiconductor element.

  In a sixth aspect of the present invention, a power semiconductor element in which a wide band gap semiconductor material is applied to the power semiconductor element driven by the gate driving circuit of the voltage-driven power semiconductor element in the first to fifth aspects is used. And

  In a seventh aspect, the wide band gap semiconductor material according to the sixth aspect is characterized by being composed of one or a combination of any of silicon carbide, gallium nitride, gallium oxide and diamond.

In the present invention, a short-circuit current detecting means for detecting a short-circuit current flowing in the power semiconductor element and a short-circuit current integrating means for integrating the current detection value are provided, and the integrated value of the short-circuit current integrating means is equal to or greater than a set value. In this case, the gate is forcibly shut off. As a result, it is possible to detect an overcurrent state even during a current rising period in which a large noise signal is superimposed in a transient state at the time of switching, and the conventional non-detection time provided to prevent erroneous detection of an arm short circuit is shortened or eliminated. Therefore, it is possible to quickly detect an arm short circuit. As a result, highly reliable short circuit protection is possible.
Further, by applying a switching element such as a MOSFET or IGBT made of a wide band gap semiconductor material such as silicon carbide as a voltage-driven power semiconductor element, a drain current which is a main circuit current when the gate driving voltage is reduced. Alternatively, the collector current can be reduced at a high speed, and the short-circuit current and the surge voltage can be further reduced.

1 is a circuit diagram showing a first embodiment of the present invention. FIG. 5 is an operation waveform diagram when the arm is short-circuited according to the first embodiment of the present invention. It is a circuit diagram which shows the 2nd Example of this invention. It is an operation | movement waveform diagram at the time of the arm short circuit by the 2nd Example of this invention. It is an example of a block diagram of a three-phase inverter system. It is a conventional gate drive circuit diagram with overcurrent protection. It is a figure for demonstrating short circuit current operation | movement. It is an example of an overcurrent detection circuit system diagram. It is an example of a current waveform at the time of IGBT ON. It is an example of an operation waveform figure at the time of arm short circuit protection in a conventional system. It is an example of a current waveform in which noise is superimposed at the time of turn-on.

  The gist of the present invention is that in a gate drive circuit for driving a voltage-driven power semiconductor element applied to a power converter, a short-circuit current detecting means for detecting a short-circuit current flowing in the power semiconductor element, and integrating the detected current value Short-circuit current integrating means is provided, and when the integrated value of the short-circuit current integrating means exceeds a set value, the gate is forcibly cut off.

  FIG. 1 shows a first embodiment of the present invention. An integration circuit 30 for integrating a current detection signal 23 obtained by converting a current detected by the sense IGBT 21 into a voltage by a resistor 22 and an integration time setting circuit 31 for determining an operation period of the integration circuit 30 are added to the conventional circuit example of FIG. This is the configuration. The description of the same parts as those of the conventional circuit is omitted.

Integration time one-shot circuit 31 for setting forms a t _i component of the pulse to be in the trigger integration time a rise of the gate drive command signal 13 is input to the integrating circuit 30 (signal 32). The integration circuit 30 receives the input of the signal 32 and integrates the voltage 23 corresponding to the current detected by the sense IGBT 21. When the comparator circuit 25 determines that the integrated value has become equal to or greater than the set value (Q _det ) of the voltage setting unit 33 within the period t _i , it is determined that the arm short circuit current is flowing, and the signal latch is performed. The switch circuit 24 is operated through the intended SR flip circuit 35 to perform forced cutoff. Here, the integration time t _i needs to be shorter than the short-circuit tolerance time of the IGBT to be protected.

FIG. 2 shows an example of operation waveforms when the arm is short-circuited by this circuit. It can be seen that the gate signal is cut off when the integrated waveform of the IGBT current Ic reaches the set value (Q _det ) of the setter 33, and the gate voltage V _GE is gradually lowered. Since the integration circuit 30 is used for current detection, stable detection is possible even in the case of a waveform with superimposed noise as shown in FIG. In this example, an example of soft shut-off is shown, but even if it is not soft cut-off, it can be applied even in the case of hard cut-off by reducing wiring inductance, strengthening a snubber circuit, and the like.

FIG. 3 shows a second embodiment of the present invention. The on-delay timer circuit 34 for determining the time until the integration operation is started is added to the first embodiment. On-delay timer circuit 34 is a circuit for delaying (t _d min) the rise time of the gate drive command signal 13. Circuit 31 forms a t _i component of pulse output signal becomes integration time to the trigger from the delay circuit 34, and inputs (signal 32) to the integrating circuit 30. The integrating circuit 30 receives the input of the signal 32 and integrates the voltage 23 corresponding to the current of the sense IGBT. When this integrated voltage becomes equal to or higher than the voltage (Q _det ) of the voltage setting unit 33 within the period t _i, it is determined that an arm short circuit current is flowing, and the switch circuit 24 is operated via the SR flip circuit 35. Forcibly shut off. Here, the sum (t _d + t _i ) of the delay time t _d until the integration is started and the integration time t _i needs to be shorter than the short-circuit withstand time of the IGBT to be protected.

FIG. 4 shows an example of operation waveforms when the arm is short-circuited by this circuit. During the period of the delay time td of the on-delay timer circuit 34, the integration circuit 30 does not perform the integration operation, and the integration value becomes the voltage (Q _det ) of the voltage setting device 33 within the period of the integration time t _i from the integration start time. In this embodiment, the gate voltage V _GE is gradually lowered at the time to cut off. When turning on, the reverse recovery current of the diode is superimposed on the load current as shown in FIG. 11, and when the waveform (FIG. 11) in which noise is superimposed on this waveform is integrated, a current waveform that is not a short-circuit overcurrent is integrated. The integrated value is different from the value indicating the short circuit overcurrent. In order to avoid this, the integration operation is not performed in the period of the delay time td of the on-delay timer circuit 34 at the time of the on signal. In this example, an example of soft shut-off is shown, but even if it is not soft cut-off, it can be applied even in the case of hard cut-off by reducing wiring inductance, strengthening a snubber circuit, and the like.

  In the above embodiment, an IGBT is used as the switching element. However, the switching element can be realized by a voltage driven element such as a MOSFET. In particular, when a gate drive voltage is lowered by applying a switching element such as a MOSFET or IGBT made of a wide band gap semiconductor material such as silicon carbide as a voltage-driven power semiconductor element, a drain current which is a main circuit current Or the effect which can reduce a collector current at high speed is acquired.

  The present invention is a proposal related to a gate drive circuit having an overcurrent protection function in a conversion device to which a semiconductor switching element is applied, and can be applied to an inverter for driving a motor, an uninterruptible power supply, a DC power supply, and the like.

DESCRIPTION OF SYMBOLS 1 ... DC power supply 1b ... Large capacity capacitor 2 ... Inverter 3, GD1, GD2 ... Gate drive circuit 6 ... Electric motor (load)
4, Qu, Qd, Q1 ... IGBT 21 ... sense IGBT
5, 17, 18 ... Diode 7 ... Drive signal 8 ... Control circuit 34 ... On-delay timer circuit 9 ... Gate drive power supply 10 ... NPN transistor 11 ... PNP transistor 12. ..Photocouplers 14, 15, 16a, 16b, 27, 22 ... resistors 26 ... capacitors 24 ... switch circuits 25 ... comparator circuits 33 ... voltage setting devices 35 ... SR flip-flops SR ... Shunt resistor CT ... Current detector 30 ... Integrator 31 ... One-shot circuit

Claims (7)

  In a gate driving circuit for driving a voltage-driven power semiconductor element applied to a power converter, a short-circuit current detecting means for detecting a short-circuit current flowing in the power semiconductor element, and a short-circuit current integrating means for integrating the current detection value A gate drive circuit for a voltage-driven power semiconductor element, wherein the gate is forcibly cut off when the integral value of the short-circuit current integrating means is equal to or greater than a set value.   2. The gate drive circuit for a voltage-driven power semiconductor device according to claim 1, wherein the integration range of the short-circuit current integrating means is from a turn-on start time of the voltage-driven power semiconductor device to a set integration time. A gate drive circuit for a voltage-driven power semiconductor element, which is characterized.   3. The gate drive circuit for a voltage-driven power semiconductor device according to claim 2, wherein a set integration time from the turn-on start time is within an allowable short-circuit time of the voltage-driven power semiconductor device. A gate drive circuit for a drive power semiconductor element.   2. The voltage-driven power semiconductor device according to claim 1, wherein the integration start time of the short-circuit current integrating means is a set time after the turn-on start time. Device gate drive circuit.   5. The voltage-driven power semiconductor device according to claim 4, wherein the integration end time of the short-circuit current integrating means is a time when the time from the turn-on start time is within the short-circuit allowable time of the voltage-driven power semiconductor device. Gate drive circuit.   6. A voltage-driven power semiconductor element gate drive circuit according to claim 1, wherein a power semiconductor element using a wide band gap semiconductor material is used for the power semiconductor element. Gate drive circuit for power semiconductor devices. 7. The gate drive circuit for a voltage-driven power semiconductor device according to claim 6, wherein the wide band gap semiconductor material is composed of one or a combination of any of silicon carbide, gallium nitride, gallium oxide and diamond. A gate drive circuit of a voltage drive type power semiconductor element characterized by the above.

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