Power conversion device

1. A power conversion device, comprising:

a resonant inverter circuit including two or more switch elements;

a detector to detect output currents of the switch elements;

a resonance determiner to determine that a resonance frequency of the resonant inverter circuit is abnormal when a number of times, in which an absolute value of a current detected by the detector at turn-off of the switch elements is equal to or greater than a threshold, is equal to or greater than a predetermined number of times that is two or more during a predetermined period that is equal to or longer than two switching periods of the switch elements; and

a controller to cause the resonant inverter circuit to stop a switching operation when the resonance determiner determines that the resonance frequency of the resonant inverter circuit is abnormal.

2. The power conversion device according to claim 1 , wherein the resonance determiner further determines that the resonance frequency of the resonant inverter circuit is abnormal when the absolute value of the current detected by the detector for each turn-off of the switch elements continues to be equal to or greater than the threshold a predetermined number of times.

3. The power conversion device according to claim 1 , wherein the switch elements are made of a wide band gap semiconductor.

4. The power conversion device according to claim 3 , wherein the wide band gap semiconductor is made of silicon carbide, gallium nitride-based material, or diamond.

5. The power conversion device according to claim 1 , wherein the resonance determiner further comprises:

shift registers, wherein a quantity of the shift registers is determined by subtracting 1 from a value obtained by dividing the predetermined period by a switching period, the shift registers being connected in series;

a first comparator to compare an absolute value of a current value outputted by the detector with the threshold and to input a result of the comparison between the absolute value of the current value outputted by the detector and the threshold into a first shift register of the shift registers;

a subtractor into which an output value of a last shift register of the shift registers is inputted;

an adder to add, to an output of the subtractor, the result of the comparison by the first comparator; and

a second comparator to compare the output of the subtractor with the predetermined number of times,

wherein the subtractor subtracts the output value of the last shift register from an output value of the adder, and the resonance determiner outputs a result of comparison by the second comparator to the controller.