Active-Forced-Commutated Bridge Using Hybrid Devices for High Efficiency Voltage Source Converters

In high-power converters, the on-state characteristics of semiconductor devices dictate its efficiency performance even if the optimized topologies are adopted. This letter proposes an active-forced-commutated (AFC) bridge that employs the hybrid power devices of thyristor and insulated-gate bipolar transistor (IGBT) to operate as a voltage source converter or the building blocks of complex multistage high-voltage high-power converters. In this scheme, the thyristors are placed in the main power path that conducts for most of the fundamental period to lower the on-state losses; while the IGBT-based full-bridge (FB) chain-link is used for controlled (soft) transition and forced commutation of the main thyristor bridge, operating in short period. This stepped transition voltage also leads to minimized dv/dt exerted on the interfacing transformer. To coordinate the operation of these two parts, the FB stack is designed to operate in a concave polygon stepped transition mode for the ordered turn-on and turn-off of thyristors according to different categories of commutation events. Detailed commutation analysis for the AFC-bridge is provided in this letter; also, high-level discussions and simulation results are presented to demonstrate its potential technical merits.