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.