Abstract
Today, bidirectional DC converters (BDC) are playing a much more important role of key component to interface between a high-voltage bus and a low-voltage bus in power systems such as electric vehicles, renewable energy sources, uninterrupted power supplies, telecom and computer systems. The bidirectional power flow capability enables one to operate the corresponding power system such as photovoltaic systems and hybrid electric vehicles more reliably and flexibly. In fact, a BDC with galvanic isolation and high step up/down ratio as well as with soft switching characteristic for renewable energy systems is focused in this thesis. Basically, the major contributions of this thesis can be summarized as follows. First, a BDC topology consisting of a half bridge, a coupling inductor, a full bridge together with a resonant capacitor and an output capacitor is proposed to achieve high step up/down ratio, galvanic isolation and soft switching capability. The choice of the coefficient of coupling of the coupled inductors can provide one with one more degree of design flexibility for different applications. Second, some design guidelines are also provided for easy design of the BDC. Finally, a 250W prototype with 200V dc bus voltage and 24V battery voltage is implemented with a digital controller using DSP TMS320F28335 to verify the validity of the proposed converter. It is seen that a maximum efficiency of 93.3% can be achieved for forward step-down operation mode, and a maximum efficiency of 92.5% can be obtained for reverse step-up operation.