Design and Testing of a SiC-Based Solid-State Bypass Switch for 1 kV Power Electronics Building Blocks

A fault-protective bypass switch for submodules (SMs) is crucial in maintaining the power flow continuity of modular multilevel converters (MMCs). Traditionally, thyristor-based switches are employed as bypass switches in medium-voltage converters. However, an advanced modulation scheme such as switching cycle control (SCC) requires the bypass switch to conduct pulsating arm currents at switching frequencies. Therefore, a quick turn-on time for the switch is critical to regulating SM damage from the fault transients. This study investigates the bypass switch requirements for SCC-based MMCs with 1 kV full-bridge SMs compared to traditional phase-shifted carrier wave modulation. A 100 A bypass switch is designed using SiC MOSFETs to overcome the potential drawbacks of thyristor-based switches. Experimental validation of the designed bypass switch shows a short turn-on time of 142 ns, conduction at 350 A/µs di/dt-rate, and endurance to transient currents with peaks of up to 900 A.