Thyristor current interrupter

A method of operating a solid-state switching apparatus, the method comprising:

• sensing a thyristor current conducted by at least one of a pair of anti-parallel thyristors, the pair of anti-parallel thyristors being coupled in parallel with a quasi-resonant turn-off circuit, wherein the quasi-resonant turn-off circuit includes a first selectively conductive path and a second selectively conductive path;
• determining a magnitude of the sensed thyristor current and a polarity of the sensed thyristor current;
• waiting, in response to determining that the magnitude is less than a threshold value, for a time period;
• reevaluating the magnitude of the sensed thyristor current and the polarity of the sensed thyristor current after the time period has elapsed;
• and
• activating, in response to determining after the time period has elapsed that the magnitude is greater than the threshold value, one of the first selectively conductive path and the second selectively conductive path based on the polarity to commutate and interrupt the thyristor current.

A solid-state switching apparatus, comprising:

• a first thyristor that selectively couples a source with a load to conduct a load current;
• a second thyristor anti-parallel to the first thyristor, wherein the second thyristor selectively couples the source with the load to conduct the load current;
• a quasi-resonant turn-off circuit coupled in parallel with the first thyristor and the second thyristor, wherein the quasi-resonant turn-off circuit comprises a first selectively conductive path configured to commutate and interrupt the load current when the load current is conducted by the first thyristor, and wherein the quasi-resonant turn-off circuit further comprises a second selectively conductive path configured to commutate and interrupt the load current when the load current is conducted by the second thyristor;
• a sensor configured to sense the load current;
• and
• a control circuit configured to:
• determine, using the sensor, a magnitude of the load current and a polarity of the load current;
• wait, in response to determining that the magnitude is less than a threshold value, for a time period;
• reevaluate the magnitude of the load current and the polarity of the load current after the time period has elapsed;
• and
• in response to determining after the time period has elapsed that the magnitude of the load current is greater than the threshold value:
• activate the first selectively conductive path to commutate and interrupt the load current conducted by the first thyristor in response to the polarity of the load current being positive;
• and
• activate the second selectively conductive path to commutate and interrupt the load current conducted by the second thyristor in response to the polarity of the load current being negative.