Research On Two-Switch Forward Bi-Directional DC-DC Converter

Bi-directional DC-DC converter (hereinafter, BDC) can make the power flow in either direction according to external requirements, and can perform two or more functions. With the development of modern science and production, the needs of BDCs grow rapidly. The BDCs are widely used in aerospace power systems, DC uninterruptible power supplies, multi-port hybrid power supply systems and electric vehicle power systems. As the BDCs are used extensively, it is useful to reduce the size and weight of the power systems with great value of research.The one-switch forward BDC has problems of high switch voltage stress and complicated designing of the magnetic reset circuit of the transformer. Further more, in boost mode it has to use pulse overlapping method to make the inductor current commutate smoothly and to make the power flow in opposite way. However, the pulse overlapping method makes the designing of the driving circuit more complicated, the cost rise and the reliability of the system down. According to these problems existing in one-switch forward BDC, a kind of two-switch forward BDC is researched, which makes the swich voltage stress much lower and reduces the difficulties of the transformer designing. By using no pulse overlapping method can make the power-flow reverse as well through the parasitic capacitance charging-discharging by inductor current. This method improves the reliability of the system and makes the desining of the driving circuit much easier. This converter has good application prospect in occasions such as high voltage of power supply and large voltage transfer ratio. The constructure and the two operation modes in CCM (continual conduction mode of the inductor current) of the converter are analysed in details. Then the principle that the switches at the low voltage side achieved zero voltage conduction is explained, the problems of switchs current spikes caused by parasitic parameters and the suppression measures are explained as well. The feasibility of the converter that can make the power flow in opposite direction by using no pulse overlapping method is verified in theory and simulation confirmation followed. Finally, a prototype of the two-switch forward bi-directional DC-DC conveter is designed to verify the theoretical analysis and simulation results.