Research On High-Power Phase-Shifting Full Bridge DC/DC Converters

This thesis studies the key technologies in the full-bridge DC/DC converters, including solutions to soft-switching, differences between zero-voltage switching and zero-voltage zero-current switching topologies, methods for zero-current switching for lagging legs in ZVZCS topologies, common control stratigies and their differences, structure design considering thermal and EMI problems, step-by-step design of a 15kW prototype and novel optimized methods in magnetic components and feed-back control design.Zero-voltage zero-current switching full-bridge DC/DC converter, also known as ZVZCS FB DC/DC converter, is one of the most popular topologies in high-power DC/DC converters, due to its reliability, its applicability for IGBTs in high-voltage applications, and its efficiency when powering whether light load or full load. ZVZCS FB circuit has been studied sinces 90's in last century while being the focus in the industry. A large variety of topologies, in which there are no less than 10 solutions to the realization of zero-current switching in the lagging leg with advantages and disadvantages in each one of them, and controlling strategies which include phase-shifted control and limited dual-polarity control, are presented. This thesis compares these topologies and control methods by studying their principles, deriving their characteristics, and summarizing their pros and cons in different conditions.On the contrary, another soft-switching full-bridge DC/DC converter—the ZVS full-bridge DC/DC circuit, is also studied for the discussion integrality. The low efficiency when powering light loads, the difficulty in implementing ZVS in the lagging leg, the high loop current in switching device and diodes, as well as the relatively severe duty-ratio loss in ZVS FB circuits are analysed in this thesis.The thesis provides the design of a 15kW prototype introducing the ZVZCS PS FB circuit for electric system operation, with analysis of the realization of every modules. The key techniques such as the choice of scheme, the design of feed-back control loop, the snubbing of voltage spike in thesecondary side of the transformer, and thermal and EMI problems are also presented.New thoughts on the optimizing design of magnetic components and modeling of power supply systems, which are extremely important for switching-mode power supply, are inspired during the design procedure. The novel methods' principle and approach are given in the appendixes. Also practicability is discussed.Experimental results and related analysis are provided in the thesis.