Design Of Soft-Switching Bidirectional DC-DC Converter For Hybrid Electric Vehicles

With increasingly serious for the energy shortage and the environmental pollution, hybrid electric vehicles have become a common topic because of their great potential in energy conservation and environmental friendness. The hybrid electric vehicle has these features over the conventional electric vehicles, such as long battery lifetime, high power density and high energy utilization. It has become an inevitable trend of the traffic industry. Hybrid electric vehicles are mainly composed of multi-energy sources, energy management systems and a motor. In order to achieve the cooperative operation for mutiple energy storage components, bidirectional DC-DC converters become one of the key parts for the total eletrical system, which will directly effect on the total conversion efficiency, performance and cost of hybrid electric vehicles.The single-phase bidirectional DC-DC converter is usually employed for the traditional hybrid electric vehicle. However, low efficiency, low power capability and large output current ripple are its main shortcoming. In order to solve these propblems, an interleaved bidirectional DC-DC converter is proposed and developed in the thesis.Firstly, different operation modes in corresponding with running conditions of the hybrid electric vehicles are discussed. Operation priciple, parameters design and loss analyses of the interleaved bidirectional DC-DC converter with continuous conduction mode are introduced. Unfornately, this operation mode results in the large inductor volume, low efficiency and low reliability. Therefore, the synchronous conduction mode is studied. The proposed operation mode realizes the zero-voltage-switching of main switches. Thus the overall efficiency is increased greatly. Furthermore, the small signal model for bidirectional DC-DC converters operating in charging mode and discharging mode are derived, respectively. The digital controllers for two modes are designed and optimized for improving the steaty-state and transist performance of the converter.A 1.5kW experimental prototype has been designed, fabricated and tested in the lab. The steaty-state experiment results operating in CCM and SCM are presented, respectively. The feasibility and validity of the studied method are demonstrated well by the experimental results. Finally, the advantages and disadvantages of two control schemes are summarized and compared. An improved proposal is put forward for solving the lager circuiting current at light load.