Thermal stress and high temperature effects on power devices in a fault-resilient NPC IGCT-based converter

The integrated gate commutated thyristor (IGCT) and the press-pack power diodes are successfully applied in medium-voltage Neutral Point Clamped (NPC) converters in the power range from hundreds of kW to tenth of MW. Responsible for driving key processes in various industries, the requirements of reliability and high availability of these converters are absolutely relevant, since its repair or replacement may take too much time. Given the vital importance of such equipment for the electric drive systems, they are equipped with protection schemes which are usually reliable but not infallible. If the protection scheme of the converter does not work properly in a fault situation, serious damages may be expected in the power semiconductor devices. These catastrophic effects can be alleviated by a fault-resilient design of the converter´s bus bars, limiting the damage pattern in the converter to their least complex parts. In this work the thermal behavior of the power semiconductors is investigated using finite element models in the COMSOL Multiphysics software. Simulations and experimental measurements are made to attest the effectiveness of the fault-resilient design.