A High-Power Input-Parallel Output-Series Buck and Half-Bridge Converter and Control Methods

The two-switch cascade converter is the most appropriate solution for efficient high-power applications among the existing converter topologies. However, the cascade structure and the nonlinear dc gain of boost circuit are more likely to cause severe oscillations if the criterion for the selection of the operation mode is chosen improperly during step-up/step-down transition. A novel high-power input-parallel output-series buck-half-bridge (IPOSBHB) converter is proposed in this paper. The circuit structure, operating principles, and basic relations are analyzed. Comparisons between IPOSBHB and two-switch cascade converter are also elaborated on with respect to voltage and current stress, total volume of magnetic components, and efficiency. In addition, the inconformity of the transfer functions, the discontinuity caused by the switching time delay, and the disturbance of input voltage are analyzed. Methods for compensation are also proposed. The proposed converter can achieve satisfactory comprehensive performance when the step-up ratio is low. The combinational control strategy and the compensation methods proposed in this paper are easy to carry out in order to achieve effective control at steady state, smooth transition at mode change, and reduction of the adverse effect caused by the disturbance of input voltage. A 15-kW prototype is used to validate the proposed theory.