JP2017130985A - Semiconductor element driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that a semiconductor module is subjected to overvoltage breakdown by a free-wheeling diode on the turn-off side even though currents of insulated gate semiconductor elements connected in parallel with each other are equalized.SOLUTION: A semiconductor element driving device comprises: a detection circuit for detecting a voltage slope dv/dt of a free-wheeling diode depending on collector-emitter voltage of insulated gate semiconductor elements of one arm out of upper and lower arms in each of which semiconductor modules are series connected; and a reference voltage suppression circuit for calculating a suppression amount of a reference voltage based on a difference between a voltage signal from the detection circuit and a preset reference signal of the free-wheeling diode voltage dv/dt and calculating an output voltage Vout based on a difference between the reference voltage suppression amount and a collector reference voltage of the insulated gate semiconductor element, in which the output voltage Vout of the reference voltage suppression circuit is output as a collector reference voltage Vref of a constant current circuit of the other arm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a drive device for a semiconductor element, and more particularly to a gate drive device when insulated gate semiconductor elements are connected in parallel.

  A large-capacity power conversion device has a configuration in which insulated gate semiconductor elements (hereinafter simply referred to as IGBTs) such as IGBTs are connected in parallel. FIG. 2 shows an example of a three-phase configuration of the power converter. Each phase of the upper arm consists of an IGBT module with IGBT-U1 and IGBT-U2 connected in parallel, and each phase of the lower arm consists of an IGBT module with IGBT-D1 and IGBT-D2 connected in parallel, each connected to a DC power supply The connection points of the upper and lower arms are u, v. AC output terminal for w. It is desirable that the IGBT-U1 and IGBT-U2, and the IGBT-D1 and IGBT-D2 that constitute the IGBT module connected in parallel have good current balance.

Japanese Patent Application Laid-Open No. H10-228707 is known as one that drives a plurality of IGBTs connected in parallel equally with a predetermined current in parallel. FIG. 3 shows a gate drive circuit described in Patent Document 1. In FIG. The collector current of the IGBT is monitored by the sensor circuit 11, the signal Vsens output from the sensor circuit 11 is fed back to the constant current circuit 7, and compared with the reference voltage Vref of the collector of the IGBT so that the collector current becomes equal. The turn-on ability of the IGBT is adjusted. The constant current circuit 7 includes a p-FET current mirror circuit p-FET 6a, b for supplying a gate current to the IGBT, and operational amplifier circuits 5a-5c for supplying a current command to the p-FET 6a, b. Generates a current command for the current mirror circuit p-FETs 6a and 6b. At this time, if the output voltage of the operational amplifier circuits 5a to 5c is V ₀ , and the resistance value of the resistor 5b is Rref, a constant current I ₀ that satisfies I ₀ = V ₀ / Rref is output.

When the operational amplifier circuit 5a~5c is operated, the current I ₀ flowing through the n-FETs 5a. At the same time the current mirror circuit p-FET 6a, b is operated, even with same current flows I ₀ to p-FET6a, p-FET6b also same current flows I ₀ in. By operating the current mirror circuits p-FETs 6a and 6b, the IGBT is operated while adjusting the gate current of the IGBT (ie, adjusting the charge rate of the gate charge of the IGBT).

In Patent Document 1, the collector current of each IGBT module connected in parallel is feedback-detected, the output voltage V ₀ of the operational amplifier circuits 5a to 5c is adjusted according to the detected value, and the gate current value of the IGBT is further adjusted. The current equalization of each IGBT connected in parallel is realized.

JP 2014-93836 A

  As shown in FIG. 2, in the bridge circuit constituting a general power converter, the IGBT is connected in series between the DC voltage and the upper arm side and the lower arm side. In addition, a free wheel diode is connected in reverse to each IGBT, and the parallel connected IGBT and free wheel diode are generally housed and configured as an IGBT module (semiconductor module) in one package. Also, a 2-in-1 type module configuration in which the upper and lower arm IGBT modules are housed in one package is often used.

  For example, when the IGBT of the upper arm side module shown in FIG. 2 is turned on, the free wheel diode of the lower arm side module connected in series cuts off the current. At this time, if the IGBT turn-on speed of the upper arm side module is fast, the surge voltage generated in the lower arm side module becomes steep due to the current cutoff characteristic of the freewheeling diode. This surge voltage depends on the voltage gradient dv / dt of the freewheeling diode. The higher the dv / dt, the higher the surge voltage. In Patent Document 1, since there is no means for monitoring and controlling this voltage gradient, the surge voltage cannot be suppressed, and the surge voltage may exceed the allowable value, and the IGBT or the free wheel diode in the IGBT module may be overvoltage destroyed. .

  An object of the present invention is to provide a driving device for a semiconductor element that prevents overvoltage breakdown while equalizing the currents of IGBTs connected in parallel.

The present invention relates to a power conversion device in which an insulated gate type semiconductor element and a semiconductor module each having a reflux diode connected in parallel are connected in parallel, and the parallel connected semiconductor modules are connected in series as an upper arm and a lower arm. In a driving apparatus having current equalizing means for detecting a current flowing when a semiconductor device is turned on and feeding back to a constant current circuit to generate a constant current and supplying the generated current to the gate of the insulated gate semiconductor device,
A detection circuit for detecting a voltage gradient dv / dt of the freewheeling diode from a collector-emitter voltage of the insulated gate semiconductor element of one of the upper and lower arms connected in series;
A reference voltage suppression is calculated based on the difference between the voltage signal from the detection circuit and the reference signal of the set freewheeling diode voltage dv / dt, and the output voltage is calculated based on the difference between the reference voltage suppression and the reference voltage Vref- _1. A reference voltage suppression circuit for calculating Vout is provided.
The output voltage Vout of the reference voltage suppression circuit is configured to be output as the collector reference voltage Vref of the constant current circuit of the other arm.

The detection circuit of the present invention includes a resistor for detecting a voltage gradient dv / dt from a terminal voltage of a freewheeling diode generated when the insulated gate semiconductor element is turned off, and an operational amplifier for calculating the voltage gradient from the divided voltage. ,
The output of the detection circuit is sent to the reference voltage suppression circuit through an insulating means in which the input voltage and the output voltage are substantially the same value,
The reference voltage suppression circuit calculates the reference voltage suppression based on the difference between the input voltage and the reference signal of the preset freewheeling diode voltage dv / dt, and calculates the calculated reference voltage suppression and the set reference The output voltage Vout is calculated based on the difference from the voltage Vref- ₁ .

  The insulated gate semiconductor element of the present invention is an IGBT.

  As described above, according to the present invention, it is possible to suppress the surge voltage of the semiconductor module by suppressing the voltage rise of the return diode on the turn-off side while equalizing the collector current of each insulated gate semiconductor element. .

The schematic block diagram of the principal part which shows embodiment of this invention. The block diagram of IGBT parallel inverter. FIG. 10 is a partial view of a conventional drive circuit for an insulated gate semiconductor device.

  FIG. 1 shows a block diagram of the present invention. U, v. This corresponds to the upper arm and the lower arm of any phase of w. Here, an example of IGBT-U1 and IGBT-D1 of the IGBT module in the u phase is shown. Moreover, the current equalization means of IGBT comprised by the elements 1-5 is the same as that of patent document 1. That is, a constant current is supplied to the gate of the IGBT by a constant current circuit including the current mirror circuit 3 and the current control circuit 2. The current that flows when the IGBT is turned on is detected by the current detection circuit 1, and the detected current is fed back to the constant current circuit to flow a constant current. The switching circuit 5 switches the signal level according to the drive signal and operates one of the constant current circuit, the discharge circuit 4 or the current mirror circuit 3 to turn on or off the IGBT.

  In the present invention, the current equalization means of Patent Document 1 is provided with an overvoltage suppressing function. Reference numeral 6 denotes a detection circuit, which is composed of voltage dividing resistors R6a and R6b for the voltage Vf (collector-emitter voltage of the IGBT module) of the freewheeling diode Fw of the lower arm, an operational amplifier U1, a capacitor C, and a resistor R6c for detecting the voltage gradient. The The resistor R6a has a resistance value Ra, the resistor R6b has a resistance value Rb, and the resistor R6c has a resistance value Rc. The capacitor C has a capacitance value C.

7 is an insulating means, and 8 is a reference voltage suppression circuit, which has an operational amplifier U2 for an arithmetic circuit for suppressing the reference voltage and an operational amplifier U3 for suppression. Resistors R81 and R82 having the same resistance value Rd are connected to the negative terminal (inverting terminal) of the operational amplifier U2. A voltage gradient detection signal is input through the resistor R81, and a preset voltage gradient reference voltage Vref- ₂ is input through the resistor R82. D is a diode for an operational amplifier output limiter, and R83 is a resistor having a resistance value Re.

The output of the operational amplifier U2 is input to the negative terminal of the operational amplifier U3 through the resistor R84, and the reference voltage Vref- ₁ is input to the positive terminal through the resistor R85. The reference voltage Vref- ₁ corresponds to the reference voltage Vref- ₁ of FIG. Resistors R84 and R85 have the same resistance value, and resistors R86 and R87 have the same resistance value.

In the configuration configured as described above, the detection circuit 6 divides the voltage Vf of the freewheeling diode Fw generated when the IGBT is turned off by the resistors R6a and R6b. The divided output voltage Vf1 is
Vf1 ＝ Vf × Rb / (Ra + Rb)
It is represented by The output Vf2 of the operational amplifier U1 for voltage slope detection is
Vf2 = −Rc · C · dVf1 / dt = −Rc · C × Rb / (Ra + Rb) · dVf / dt
Thus, the slope of the voltage Vf of the free wheeling diode Fw is detected. Here, Rc and C are adjusted so that a constant output in the negative direction is output at a predetermined dVf / dt during the rise of the voltage Vf of the free wheeling diode Fw.

  Since the reference potentials of the gate driver of the IGBT and the detection circuit 6 are different, the detection voltage Vf2 is insulated by the insulation means 7 and sent to the reference voltage suppression circuit 8. In the insulating means 7, an input voltage and an output voltage having the same value are applied.

The reference voltage suppression Vs that is the output of the operational amplifier U2 is output when the absolute value of the voltage slope detection Vf2 becomes larger than the voltage slope dV / dt reference voltage Vref- _{2 of} the freewheeling diode. The reference voltage suppression component Vs is
Vs = (Vf2−Vref- ₂ ) ・ Re / Rd
Calculated by However, since it is necessary to detect only the rising edge of the freewheeling diode voltage, the limiter diode D prevents the reference voltage suppression Vs from going in the negative direction so that the output at the rising edge is not output. Note that the value of the reference voltage Vref- ₂ may be set by an actual measurement value of dV / dt measured from actual machine confirmation, or a reference value of dV / dt described in an IGBT data sheet may be used. The value of Re / Rd is set by searching for a value that can sufficiently suppress the surge voltage of the freewheeling diode Fw by checking the actual machine.

Reference voltage suppression component Vs is input to the operational amplifier U3, the reference voltage Vref- ₁ only from Vs subtracted value is output Vout of the reference voltage suppressing circuit 8 (= Vref- ₁ -Vs), and the finally are turned on The reference voltage Vref of the collector of the IGBT-U1 is input to the current control circuit 2.

As described above, according to the present invention, when the voltage gradient dV / dt of the freewheeling diode at the turn-off time of the IGBT module on the lower arm side in the power conversion device is equal to or higher than the reference value, a surge voltage is likely to be generated. The output Vout of the reference voltage suppression circuit is corrected to a value lower than the reference voltage Vref- ₁ . By this correction, the gate current of the IGBT on the upper arm side is reduced, and the rise of the gate voltage becomes gentle. Since the rise of the gate voltage becomes gradual, the turn-on speed of the upper arm side IGBT becomes slow, and the surge voltage of the freewheeling diode on the lower arm side is suppressed.

  In the above description, the upper arm side IGBT is turned on, but the same operation is performed when the lower arm side IGBT is turned on. Further, the power conversion device is not limited to an inverter circuit that converts a DC voltage into an AC voltage as shown in FIG. 2, but can also be applied to an inverter circuit that converts an AC voltage into a DC voltage. Further, the IGBT as the switching element may be replaced with another insulated gate semiconductor element such as a MOS-FET.

  According to the present invention, in a circuit in which IGBT modules connected in parallel are connected in series with upper and lower arms, the voltage rise of the return diode on the turn-off side is suppressed while equalizing the collector current of each IGBT, and the IGBT module Surge voltage can be suppressed.

DESCRIPTION OF SYMBOLS 1 ... Current detection circuit 2 ... Current control circuit 3 ... Current mirror circuit 4 ... Discharge circuit 5 ... Switching circuit 6 ... Detection circuit 7 ... Insulation means 8 ... Reference voltage suppression circuit

Claims (3)

A power conversion device in which an insulated gate semiconductor element and a semiconductor module each having a reflux diode connected in parallel are connected in parallel, and the parallel connected semiconductor modules are connected in series as an upper arm and a lower arm, In a driving apparatus having current equalizing means for detecting a current flowing at turn-on and feeding back to a constant current circuit to generate a constant current and supplying the generated current to the gate of the insulated gate semiconductor element,
A detection circuit for detecting a voltage gradient dv / dt of the freewheeling diode from a collector-emitter voltage of the insulated gate semiconductor element of one of the upper and lower arms connected in series;
The reference voltage suppression is calculated based on the difference between the voltage signal from the detection circuit and the reference signal of the set freewheeling diode voltage dv / dt, and the output voltage is calculated based on the difference between the reference voltage suppression and the reference voltage Vref- _1. A reference voltage suppression circuit for calculating Vout is provided.
A drive device for a power conversion device configured to output an output voltage Vout of a reference voltage suppression circuit as a collector reference voltage Vref of the constant current circuit of the other arm. The detection circuit includes a resistor that detects a voltage gradient dv / dt from a terminal voltage of a freewheeling diode that is generated when the insulated gate semiconductor element is turned off, and an operational amplifier that calculates the voltage gradient from the divided voltage.
The output of the detection circuit is sent to the reference voltage suppression circuit through an insulating means in which the input voltage and the output voltage are substantially the same value,
The reference voltage suppression circuit calculates a reference voltage suppression based on a difference between the input voltage and a reference signal of the preset freewheeling diode voltage dv / dt, and the calculated reference voltage suppression is set as the above-described reference voltage suppression circuit. 2. The drive device for a power converter according to claim 1, wherein the output voltage Vout is calculated based on a difference from the reference voltage Vref- ₁ . The drive device for a power converter according to claim 1, wherein the insulated gate semiconductor element is an IGBT.

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