The subject of this thesis is a high voltage (HV) to low voltage (LV) DC/DC converter in hybrid (HEVs) and electric vehicles (EVs). The focus is on use of an IGBT-based zero voltage transition (ZVT) phase shift (PS) full bridge (FB) topology for this application. Challenges when designing the IGBT-based ZVT PS FB converter are high switching frequency, wide input voltage range and wide range of load currents. In order to use the available energy of the HV battery of (H)EVs more efficiently, cost-effective loss reduction is one of the main objectives in the development of automotive HV to LV DC/DC converters.
To offer a solution for the problem of reduced efficiency due to the wide input voltage range, a new efficiency optimized single-stage reconfigurable topology is proposed. The proposed topology solves the problem of reduced converter efficiency in the upper range of HV battery voltages by adapting the transformer turns ratio depending on the input voltage. The topology is based on the ZVT PS FB converter that is during its operation, depending on the instantaneous value of battery voltage, reconfigured into a push-pull converter. The ZVT PS FB - the more efficient configuration covers upper range of input voltages whereas the hard-switching push-pull - the less efficient configuration covers the lower, less significant range. The ZVT PS configuration, due to tighter voltage range and more suitable transformer turns ratio, operates with reduced turn-off losses, significantly decreased circulating current in the freewheeling period as well as improved efficiency of the rectifier stage. The point of reconfiguration is chosen to maximize the average efficiency. Operation of the proposed converter and the efficiency improvement are validated experimentally.