A 3kW Bidirectional DC-DC Converter for Electric Vehicles

Abstract

With the global energy crisis and deteriorating environmental problems, clean and renewable energy systems have been paid more and more attention. Since then, the conventional vehicles face the increasingly serious problems of energy. In contrast, the electric vehicle (EV) technologies, which make human life greener, more eco-friendly, have continued to develop and attracted growing interest. The battery charger, which is connected from the grid to EVs, plays a critical role in the development of EVs. Generally, the storage or charging process of the battery is achieved by a bidirectional DC-DC converter (BDC), which is the key block in the EV energy system to link high voltage (HV) DC bus and low voltage (LV) DC bus. Mostly, EV is usually parked at home or a storage site overnight, then the battery charger in the vehicle can be plugged in the household utility outlets for charging. While in the day when the car is driven on the way, the battery should provide power to the motor through the BDC and another DC-AC inverter. A BDC should have high power density and high efficiency to meet the desired goals for EV’s battery charging and energy management. Therefore, this paper developed a 3kW bidirectional DC-DC converter for electric vehicles. Firstly, the advantages and disadvantages of the different kinds of BDCs are analyzed based on the characteristics of the charger. For the energy management requirements of EVs, a isolated BDC is proposed which consists of a half-bridge topology on primary side, an isolation transformer and a synchronous rectifier structure on the secondary side. It allows transfer of power between two DC buses (HV-LV) in a wide voltage-conversion range while the voltage polarity of the two buses is not changed. Meanwhile, it has the advantages of easy implementation, high efficiency, light weight and high power density. Secondly, the topology configuration and operational principles are analyzed. The BDC has a half bridge-synchronous rectifier structure and then the details of the two modes (step-down and step up) are illustrated. In addition, the circuit is designed with standard of 3kW, including the design of main circuit parameters, transformer, inductor and control scheme. Then an experimental prototype is proposed to verify the theoretical analysis. Finally, the experiments are performed in both operational modes with the prototype. The experimental waveforms are obtained which can verify the research on the 3kW bidirectional DC-DC converter for electric vehicles.