Drive circuit for power semiconductor element

1. A drive circuit for a power semiconductor element having a first terminal, a second terminal, and a gate terminal, the drive circuit comprising:

a control command unit that outputs a turn-on command for the power semiconductor element;

a gate voltage detection unit that detects a gate voltage applied to the gate terminal after the control command unit outputs the turn-on command;

a differentiator that subjects the gate voltage detected by the gate voltage detection unit to time differentiation; and

a determination unit that determines, based on a relation between the gate voltage detected by the gate voltage detection unit and a differential value by the differentiator, whether the power semiconductor element is in a short-circuit state or not.

2. The drive circuit for a power semiconductor element according to claim 1 , wherein

the determination unit outputs a signal showing a determination result to the control command unit,

the control command unit outputs a turn-off command to the power semiconductor element when the determination unit determines that the power semiconductor element is in a short-circuit state, and

the determination unit holds an output signal when the determination unit determines that the power semiconductor element is in a short-circuit state.

3. The drive circuit for a power semiconductor element according to claim 1 , further comprising:

a first comparator that compares the gate voltage detected by the gate voltage detection unit with each of a first reference value and a second reference value; and

a second comparator that compares the differential value by the differentiator with a third reference value, wherein

the determination unit determines, based on a comparison result of the first comparator and a comparison result of the second comparator, whether the power semiconductor element is in a short-circuit state or not.

4. The drive circuit for a power semiconductor element according to claim 3 , wherein

in a graph showing the relation between the gate voltage of the power semiconductor element and a time differential value of the gate voltage, the first reference value, the second reference value, and the third reference value are included in a region surrounded by: a gate voltage-differential value curve of the power semiconductor element in a turn-on operation in a normal state; and a gate voltage-differential value curve of the power semiconductor element in the turn-on operation in an arm short-circuit state, and

the determination unit determines that the power semiconductor element is in a short-circuit state when the gate voltage detected by the gate voltage detection unit is greater than the first reference value and smaller than the second reference value, and when the differential value of the differentiator is greater than the third reference value.

5. The drive circuit for a power semiconductor element according to claim 1 , wherein

a voltage applied to the first terminal is higher than a voltage applied to the second terminal,

the gate voltage detection unit includes

a current detector that detects a gate current that flows into the gate terminal of the power semiconductor element, and

an integrator that integrates the gate current detected by the current detector, and

the gate voltage detection unit detects the gate voltage of the power semiconductor element based on a value obtained by dividing an integral value of the integrator by a capacitance between the gate terminal and the second terminal.

6. The drive circuit for a power semiconductor element according to claim 1 , wherein

the gate voltage detection unit includes

a voltage detector that detects the gate voltage of the power semiconductor element,

a current detector that detects a gate current that flows into the gate terminal of the power semiconductor element,

an integrator that integrates the gate current detected by the current detector, and

a computing unit that computes an average value of the gate voltage detected by the voltage detector and an integral value by the integrator, and

the gate voltage detection unit detects the gate voltage of the power semiconductor element based on a computed value by the computing unit.

7. The drive circuit for a power semiconductor element according to claim 1 , wherein

a voltage applied to the first terminal is higher than a voltage applied to the second terminal,

the gate voltage detection unit includes

a voltage detector that detects the gate voltage of the power semiconductor element,

a current detector that detects a gate current that flows into the gate terminal of the power semiconductor element,

a first computing unit that computes an amount of voltage drop in a gate resistance based on a value obtained by multiplying the gate current, which is detected by the current detector, by the gate resistance,

a second computing unit that subtracts the amount of voltage drop in the gate resistance from the gate voltage detected by the voltage detector, the amount of voltage drop being computed by the first computing unit,

an integrator that integrates the gate current detected by the current detector, and

a third computing unit that computes an average value of:

a value obtained by dividing an integral value of the integrator by a capacitance between the gate terminal and the second terminal; and

a computed value by the second computing unit, and

the gate voltage detection unit detects the gate voltage of the power semiconductor element based on a computed value by the third computing unit.

8. The drive circuit for a power semiconductor element according to claim 1 , wherein the power semiconductor element is an IGBT.

9. The drive circuit for a power semiconductor element according to claim 1 , wherein the power semiconductor element is a MOSFET.

10. The drive circuit for a power semiconductor element according to claim 9 , wherein the power semiconductor element is a SiC element.