Analysis of light and no‐load operation of a 300 kW resonant single active bridge based on 3.3 kV SiC‐devices

Abstract The resonant single active bridge topology (R‐SAB) operated in the half‐cycle discontinuous current mode (HC‐DCM) is a very attractive solution due to its high efficiency, low complexity and fixed voltage transfer ratio (DCX). However, as expected for a series‐resonant converter (SRC), its DCX operation depends on the resonant tank circuit‐parameters, parasitic capacitive elements and output load. Specially, at light and no‐load operation, when the system is extremely underdamped, it may present a large output overvoltage due to resonance interactions. This is of prime importance for converters using medium voltage (MV) SiC‐MOSFETs, which feature significant output capacitances that can lead to voltage breakdown of the rectifier semiconductors. Therefore, the supposed fixed‐voltage transfer ratio is not entirely valid and deserves a proper understanding due its criticality. This paper reviews the subject, clarifying its root cause and its multifactorial dependencies. Moreover, it provides a simple solution based on a variable dead‐time with fixed magnetizing current experimentally verified with a 300kW/1.8kV R‐SAB prototype implemented with MV SiC‐devices.