Solid-State Circuit Breaker for Alternating Current Applications

Abstract

This thesis investigates Solid-State Circuit Breakers (SSCBs) for alternating current (AC) power systems. The increasing use of power electronics, electrification and distributed renewable generation creates a need for fast, controllable fault protection. SSCBs address this need through semiconductor switching, while introducing challenges related to conduction losses, voltage clamping and energy management. The work reviews AC fault behavior and compares electromechanical, hybrid and solid-state interruption technologies. Silicon and wide-bandgap power devices are assessed in terms of their static and dynamic characteristics, voltage and current ratings, and suitability for SSCB applications. The analysis also examines bidirectional AC topologies, gate driving, fault detection and auxiliary protection circuits. Single-phase and three-phase Simulink models are used to study fault interruption, current limiting and the energy absorbed by metal-oxide varistors (MOVs). The results demonstrate fast interruption before the natural current zero and show that repeated switching during current limiting can substantially increase cumulative MOV energy. A controlled freewheeling path is investigated in simulation to divert energy to a resistive branch and reduce MOV stress. The three-phase analysis also considers common tripping, unequal loading of the phase clamping elements and protection of local synchronous generation. Laboratory experiments on commercial onsemi SSCB evaluation boards complement the simulations. The tests include manual and processor-based control, automatic over- current interruption, parallel operation, response-time measurement and comparison with an electromechanical contactor. An external controller acquires board measurements through SPI and implements the protection logic. The experiments confirm rapid interruption independently of the natural current zero and quantify the latency of the digital control chain. Parallel operation gives close steady-state current sharing but unequal external branch currents during turn-off despite a common command; the dominant cause is not isolated. Overall, the work identifies energy management and transient coordination as essential design considerations alongside interruption speed, with experimental validation of the freewheeling path and further investigation of parallel switching remaining as future work.