A Four Switch SiC Solid State Relay with Inrush Current Protection for High Voltage and High Power Converters

This paper proposes a new four-switch configuration for a solid-state relay (SSR) with an inrush current limiting feature for high-voltage and high-power converters. A solid-state relay is a non-mechanical circuit breaker with no moving parts. It is used to disconnect a power electronic converter from its source in case of any faults or during normal shutdown. Conventionally, a solid state relay is made up of two back-to-back connected semiconductor switches like MOSFETs for bidirectional control of power. The new proposed arrangement of four N-channel MOSFETs, along with a resistor for a solid state relay, provides a 25% reduction in conduction losses compared to the conventional two MOSFET arrangement. It also charges the capacitor bank of the converter during startup with a limited peak inrush current value without any additional pre-charge circuit. Thus a converter using the proposed arrangement for a solid-state relay would be more reliable, compact, cost-effective, and efficient when compared with a conventional setup using a two MOSFET solid-state relay and a separate pre-charging circuit. A thermal model of a 1200V SiC MOSFET from Infineon was created in PLECS software, and compared with the conventional arrangement of the MOSFETs for the solid-state relay. An 800V 35KVA three-phase voltage source inverter was used to compare their performance and losses.