JP2009278704A - Gate drive of voltage-driven semiconductor device - Google Patents

Abstract

There is a method of increasing the gate-on resistance of the IGBT of the opposite arm in order to suppress the surge voltage and the oscillation voltage when the freewheeling diode reversely recovers with a small current. There is.
A gate threshold voltage at turn-off is detected, it is determined whether this voltage value is higher or lower than a predetermined value, and gate drive conditions such as gate-on resistance and gate power supply voltage for turn-on at the next turn-on are determined. Switch. Therefore, since the gate condition is switched only when the forward current of the freewheeling diode is small, the loss during steady state does not increase.
[Selection] Figure 1

Description

  The present invention relates to a gate drive device for a voltage-driven semiconductor element applied to a power converter, and more particularly to a technique for suppressing reverse recovery surge of a freewheeling diode at a small current without detecting a current.

FIG. 5 shows a circuit configuration diagram of a known voltage source inverter using an IGBT as a voltage-driven semiconductor element. In FIG. 5, 15 is a three-phase AC power supply, 16 is a rectifier circuit, 17 is a smoothing capacitor, 18 to 23 are IGBT modules with diodes connected in antiparallel, and 24 is a motor load.
6 is an equivalent circuit diagram for one phase of the voltage source inverter shown in FIG. In FIG. 6, 29 is a smoothing capacitor, 30 is a wiring inductance of the circuit, 31 is an L load, 3 and 27 are IGBTs, 4 and 28 are free-wheeling diodes (hereinafter referred to as FWD), 26 is an IGBT module of the upper arm, and 2 is The lower arm IGBT module 25 is a gate driving device 1 (GDU1) connected to the upper arm IGBT module, and 1 is a gate driving device 2 (GDU2) connected to the lower arm IGBT module.
FIG. 7 shows a circuit diagram of the main part of the gate driving device 2. In FIG. 7, 5 and 6 are switch elements for turning on and off the IGBT, 7 is a gate-on resistance, 8 is a gate-off resistance, and 9 is an interface circuit that outputs an on signal and an off signal. This type of gate driving device is as disclosed in Patent Document 1.
In FIG. 6, when the IGBT 3 is in the ON state, a current flows through the path of the smoothing capacitor 29 → the circuit wiring inductance 30 → the L load 31 → the IGBT 3 → the smoothing capacitor 29 (ON mode). When the IGBT 3 is turned off, the collector-emitter voltage VCE of the IGBT 3 increases. When the VCE reaches the DC voltage Ed, the FWD 28 is turned on, whereby the load current IL is commutated to the FWD 28, and a current flows through the path of L load 31 → FWD 28 → L load 31 (reflux mode).

From this state, when the IGBT 3 is turned on, the FWD 28 reversely recovers, a current flows through the path of the smoothing capacitor 29 → the circuit wiring inductance 30 → FWD 28 → IGBT 3 → the smoothing capacitor 29, and the reverse recovery operation of the FWD 28 ends. The IGBT 3 is again turned on (on mode). Here, a surge voltage is generated during reverse recovery of the FWD 28.
8 and 9 show the operation waveforms of the collector-emitter voltage VCE and the collector current Ic of the IGBT 3 and the operation waveforms of the anode-cathode voltage VAK and the diode current IF of the FWD 28 when the IGBT 3 of FIG. 6 is switched. Here, FIG. 8 shows an operation waveform at a normal current with a large current, and FIG. 9 shows an operation waveform at a small current with a small current (generally about 1/10 or less of the element rated current).
The voltage VAK applied to the FWD has a higher peak value at a small current (Vp2) than a normal current (Vp1), and has a vibration waveform. This is due to the fact that the reverse recovery characteristic of the diode is increased when the current is small. A high surge voltage Vp2 and a high-frequency vibration phenomenon may lead to element destruction with an increase in generated noise in the worst case. As a method for suppressing the vibration waveform having a large peak value, there is a method of increasing the gate-on resistance value of the IGBT of the opposing arm as shown in Patent Document 2.
JP 2002-165435 A Japanese Patent Laid-Open No. 10-32976

  As described above, in order to prevent the element breakdown due to the surge voltage and the vibration phenomenon at the time of reverse recovery of a small current of FWD, in the conventional gate driving device shown in FIG. 7, by increasing the resistance value of the gate-on resistance 7 of the IGBT 3, Although the surge voltage and the vibration phenomenon can be suppressed, a method of increasing the gate resistance value and relaxing the rise of the collector current of the IGBT is disclosed in Patent Document 2, but if the gate on resistance value is increased, There is a problem that the turn-on loss at a normal current with a large current increases.

In order to solve the above-mentioned problem, in the first invention, in a gate driving device for driving a voltage-driven semiconductor element used in a power conversion device, a gate threshold voltage detecting means for detecting a gate threshold voltage at turn-off; Gate threshold voltage comparison means for comparing the gate threshold voltage value detected by the gate threshold voltage detection means with a predetermined set voltage value, and gate drive for turn-on according to the comparison result in the gate threshold voltage comparison means Switching means for switching conditions is provided.
In the second invention, the gate driving condition in the first invention is a gate resistance value for turn-on.
In the third invention, in the first invention, when the gate threshold voltage detected by the gate threshold voltage detecting means is higher than a predetermined set voltage value, the switching means has a normal resistance value for the turn-on gate resistance value. It is characterized by operating so as to have a lower resistance value.
In the fourth invention, in the first invention, when the gate threshold voltage detected by the gate threshold voltage detecting means is lower than a predetermined set voltage value, the switching means has a normal resistance value for the turn-on gate resistance value. It is characterized by operating so as to have a higher resistance value.
The fifth invention is characterized in that the gate drive condition in the first invention is a turn-on gate drive power supply voltage.

In the sixth invention, the switching means in the first invention is such that when the gate threshold voltage detected by the gate threshold voltage detecting means is higher than a predetermined set voltage value, the turn-on gate drive power supply voltage value is normal. It operates so that it may become a voltage value higher than a power supply voltage value.
In the seventh invention, the switching means in the first invention is such that when the gate threshold voltage detected by the gate threshold voltage detecting means is lower than a predetermined set voltage value, the turn-on gate drive power supply voltage value is normal. It operates so that it may become a voltage value lower than a power supply voltage value.

  In the present invention, the gate threshold voltage at the turn-off time of the self-arm element is detected, it is determined whether the voltage value is higher or lower than a predetermined value, and the gate drive condition at the next turn-on is switched. As a result, without increasing the turn-on loss when the current is large, the surge voltage and vibration phenomenon at the time of reverse recovery of the small current of the FWD can be suppressed, and the generated noise can be reduced and the element breakdown can be prevented.

  The gist of the present invention is to detect the gate threshold voltage when the self-arm element is turned off, determine whether the voltage value is higher or lower than a predetermined value, and switch the gate driving condition at the next turn-on. . As shown in FIG. 10, the gate threshold voltage VGE is low when the collector current Ic is small, and is high when the collector current is large. The present application focuses on this characteristic, and switches the gate drive condition by detecting the gate threshold voltage at turn-off without detecting the current.

FIG. 1 shows a first embodiment of the present invention. Components having functions similar to those of the conventional example of FIG. The gate driving device according to the present invention is different from the conventional gate driving device (FIG. 7) in that a gate threshold voltage detecting circuit 12 for detecting a gate threshold voltage at the time of turn-off operation, a detected gate threshold voltage value and a predetermined set voltage. A gate threshold voltage comparison circuit 13 that compares values, a resistance value selection circuit 14 that selects a gate-on resistance value according to the result of the gate threshold voltage comparison circuit 13, and a switching element 10 that drives the IGBT 3 with a high resistance 11 during small current reverse recovery Is a connected configuration.
Next, the operation of the gate driving apparatus according to the present invention will be described with reference to FIGS. 2 shows an operation waveform at a normal current with a large current, and FIG. 3 shows an operation waveform at a small current with a small current. In FIG. 1, when an off signal is output from the interface circuit 9, the switch element 6 is turned on, the gate voltage VGE decreases, and the collector-emitter voltage VCE starts increasing. At this time, since the collector current Ic cannot be commutated to the FWD of the opposing arm until the VCE reaches the power supply voltage Ed, the gate voltage VGE is a gate threshold voltage VGE (th) corresponding to the collector current value Ic. Clamped. When the gate threshold voltage detection circuit 12 detects the gate threshold voltage VGE (th), the gate threshold voltage comparison circuit 13 compares the detection voltage VGE (th) with a predetermined set voltage VGE (0).

Here, if the comparison result of the gate threshold voltage comparison circuit 13 is VGE (th)> VGE (0) (see FIG. 2), the resistance value selection circuit 14 has a normal FWD of the opposing arm at the next turn-on. A normal gate-on resistance 7 is selected on the assumption that reverse recovery is caused by the current. If the comparison result is VGE (th) <VGE (0) (see FIG. 3), the resistance value selection circuit 14 estimates that the FWD of the opposing arm at the next turn-on reversely recovers with a small current. The resistance gate-on resistance 11 is selected.
Next, when an ON signal is output from the interface circuit 9, if the normal gate-on resistance 7 is selected from the above, the switch element 5 is turned ON, and the IGBT 3 is turned on by the normal gate-on resistance 7. When the high resistance gate-on resistance 11 is selected, the switch element 10 is turned on, and the IGBT 3 is turned on by the high resistance gate-on resistance 11.
As a result, when the FWD of the opposing arm reversely recovers with a normal current having a large current, the IGBT can be turned on with a normal resistance, and when reversely recovered with a small current, the IGBT can be turned on with a high resistance. It is possible to suppress the surge voltage and vibration phenomenon when the FWD reversely recovers with a small current without increasing the turn-on loss.

It can be realized in the same way even if the resistance value is selected so that the switch elements 5 and 10 are turned on when reverse recovery is performed with a normal current, and one of the switch elements 5 or 10 is turned on when reverse recovery is performed with a small current. Needless to say.
In addition, in a device that outputs a pulse with a small steady current, the switch element is controlled so that the resistance value increases in a steady state, and the resistance value decreases when a pulse with a large current is output. Therefore, the same effect can be exhibited. In such an apparatus, the set voltage VGE (0) is set to a steady state so that VGE (th) <VGE (0) in a steady state and VGE (th)> VGE (0) at the time of pulse output. A value higher than the threshold voltage VGE (th) may be set.

FIG. 4 shows a second embodiment of the present invention. Components having functions similar to those of the conventional example of FIG. 4, the gate driving device according to the present invention is different from the conventional gate driving device (FIG. 7) in that a gate threshold voltage detecting circuit 12 for detecting a gate threshold voltage at the time of turn-off operation and a detected gate threshold voltage value are predetermined. A gate threshold voltage comparison circuit 13 that compares the set voltage values, a power supply voltage value selection circuit 32 that selects a power supply voltage value according to the result of the gate threshold voltage comparison circuit 13, a normal power supply voltage value ( The switch element 33 that drives the IGBT 3 with a voltage value (15V−α) lower than 15V) is connected.
Next, the operation of the gate driving apparatus according to the present invention will be described. 4, the gate threshold voltage comparison circuit 13 compares the detected gate threshold voltage VGE (th) with a predetermined set voltage VGE (0) as in the above-described embodiment of FIG. If the comparison result of the gate threshold voltage comparison circuit 13 is VGE (th)> VGE (0), the power supply voltage value selection circuit 32 reversely recovers the FWD of the opposing arm at the next turn-on with a normal current having a large current. The normal power supply voltage value (15 V) is selected. If the comparison result is VGE (th) <VGE (0), the power supply voltage value selection circuit 32 estimates that the FWD of the opposing arm at the next turn-on will reversely recover with a small current, and the normal power supply voltage value A lower voltage value (15V-α) is selected. Here, α is selected to an arbitrary value corresponding to the element characteristics.

Next, when an on signal is output from the interface circuit 9, if the normal power supply voltage value is selected from the above, the switch element 5 is turned on, and the IGBT 3 is turned on at the normal power supply voltage value (15V). do. When a voltage value lower than the normal power supply voltage value is selected, the switch element 33 is turned on, and the IGBT 3 is turned on at a voltage value (15V−α) lower than the normal power supply voltage value.
As a result, when the FWD of the opposing arm reversely recovers with a normal current having a large current, the IGBT is turned on with a normal power supply voltage, and when reversely recovered with a small current, the IGBT is turned on with a power supply voltage lower than normal. It is possible to suppress the surge voltage and vibration phenomenon when the FWD is reversely recovered with a small current without increasing the turn-on loss during normal current operation.
The power supply voltage is configured as a series circuit of two power supply voltages, and is configured to output the power supply voltage for the series when outputting a high voltage, and one of the power supply voltages when outputting a low voltage. However, the same function can be exhibited.
In addition, in a device with a pulse output with a small steady current, each switch element is controlled so that the power supply voltage is low in a steady state and the power supply voltage is high when a pulse with a large current is output. Therefore, the same effect can be exhibited. In such a device, the set voltage VGE (0) is set so that VGE (th) <VGE (0) in a steady state where the current is small and VGE (th)> VGE (0) when a pulse with a large current is output. ) May be set to a value higher than the threshold voltage VGE (th) in the steady state.

  Furthermore, it goes without saying that the present invention has the same effect when applied to a power converter in which a plurality of IGBTs are connected in series to each arm.

  The present invention is particularly effective when applied to a device having a large load power fluctuation or a device having a large change in output current waveform. It can be applied to variable speed inverters, pulse power supplies, reactive power compensators, uninterruptible power supplies (UPS), and the like.

1 shows a first embodiment of the present invention. FIG. 2 is a first operation waveform diagram for explaining the operation of FIG. FIG. 6 is a second operation waveform diagram for explaining the operation of FIG. 1. 2 shows a second embodiment of the present invention. The circuit block diagram of a voltage type inverter is shown. FIG. 6 is an equivalent circuit diagram for one phase of FIG. 5. A conventional gate drive circuit diagram is shown. FIG. 8 is an operation waveform diagram at normal current in FIG. 7. The operation waveform figure at the time of the small electric current in FIG. 7 is shown. The Vce-Ic characteristic with respect to the gate voltage VGE is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 25 ... Gate drive circuit 2, 18-23, 26 ... IGBT module 3, 27 ... IGBT 4, 28 ... Freewheeling diode 5, 6, 10, 33 ... Semiconductor switch 7, 8, 11 ... Resistance 9 ... Interface circuit 12 ... Gate threshold voltage detection circuit 13 ... Gate threshold voltage comparison circuit 14 ... Resistance value selection circuit 32 ... Power supply voltage value selection circuit 15 ..AC power supply 16 ... rectifier circuit 17, 29 ... smoothing capacitor 24 ... motor load 30 ... wiring inductance 31 ... L load

Claims (7)

  In a gate driving device for driving a voltage-driven semiconductor element used in a power converter, a threshold voltage detecting means for detecting a gate threshold voltage at turn-off, and a gate threshold voltage value detected by the threshold voltage detecting means are predetermined. A voltage drive type semiconductor device comprising: gate threshold voltage comparison means for comparing a set voltage value; and switching means for switching a gate drive condition for turn-on according to a comparison result in the gate threshold voltage comparison means Gate drive device. 2. The voltage-driven semiconductor device gate driving apparatus according to claim 1, wherein the gate driving condition is a turn-on gate resistance value.   The switching means operates such that when the gate threshold voltage detected by the gate threshold voltage detection means is higher than a predetermined set voltage value, the turn-on gate resistance value is lower than the normal resistance value. 3. The gate drive device for a voltage driven semiconductor device according to claim 1, wherein the gate drive device is a voltage driven semiconductor device.   The switching means operates so that the gate resistance value for turn-on is higher than the normal resistance value when the gate threshold voltage detected by the gate threshold voltage detection means is lower than a predetermined set voltage value. 3. The gate drive device for a voltage driven semiconductor device according to claim 1, wherein the gate drive device is a voltage driven semiconductor device.   2. The voltage-driven semiconductor device gate driving apparatus according to claim 1, wherein the gate driving condition is a turn-on gate driving power supply voltage.   The switching means is configured such that when the gate threshold voltage detected by the gate threshold voltage detecting means is higher than a predetermined set voltage value, the turn-on gate drive power supply voltage value is higher than the normal power supply voltage value. 6. The gate drive device for a voltage driven semiconductor device according to claim 1, wherein the gate drive device operates as described above. The switching means is configured such that when the gate threshold voltage detected by the gate threshold voltage detecting means is lower than a predetermined set voltage value, the turn-on gate drive power supply voltage value is lower than the normal power supply voltage value. 6. The gate drive device for a voltage driven semiconductor device according to claim 1, wherein the gate drive device operates as described above.

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