Design considerations of power semiconductor devices employed in VSCs under short-circuit fault conditions in MVDC distribution grids

Electric energy distribution using medium voltage DC (MVDC) enables an advantageous performance compared to the state-of-the-art MVAC counterparts. Among others, a crucial challenge currently is related to the need for developing high-performance protection schemes against DC short-circuits and, thus, to prevent severe conditions of electric and thermal stress in the involved power electronics equipment. This paper presents an evaluation of design requirements and performance of four types of active rectifiers employed in MVDC grids under a DC short-circuit condition when using either an AC circuit breaker (AC CB) or a solid-state DC CB. The focus is on freewheeling diodes and the evaluation is performed in terms of power semiconductors stress, fault handling capability and chip area requirements by using simulations and calculations. The superior performance of DC CB over AC counterparts for all rectifier types is highlighted.