Overvoltage Suppression Scheme for Minimized Snubber Requirements in MVDC Solid-State Breakers With Series-Connected IGBTs

Abstract

Solid-state dc breakers are the ultimate technology for protecting medium-voltage dc grids having equipment vulnerable to excessive fault-current stress, due to the very short fault-clearing times. A typical implementation of such breakers is based on insulated gate bipolar transistors (IGBTs). However, as the rated voltage of the grid increases, series connection of IGBTs is inevitable and impose challenges on transient and steady-state blocking voltage distribution. This article presents a novel voltage-balancing scheme that combines passive resistive-capacitive-diode (RCD) snubber circuits and a gate driver containing a gate-current balancing magnetic-core. The proposed concept aims at minimizing the required snubber capacitances, which may be high. The impact of the proposed configuration on the breaker design and its performance are studied under different fault scenarios. Using the proposed breaker configuration, the snubber capacitance has been reduced by up to 60%. Besides, both simulations and experimental results reveal the mitigation of high peak voltage stress across the early turned-off IGBTs under gate signal propagation delays.