A compact bi-directional power-conversion system scheme with extended soft-switching range

This paper outlines a soft-switching modulation scheme based on zero-current-switching (ZCS) principle with extended range for the front-end isolated dc/dc converter of an isolated three-phase rectifier-type high-frequency-link (RHFL) power converter. General modulation methodology and optimization conditions are presented, and with the help of linear programming, the optimum solution for a particular objective function can be achieved to implement the proposed ZCS scheme. In conjunction with a back-end ac/ac converter operating with a novel patent-filed hybrid modulation scheme which reduces the number of hard-switched commutation per switching cycle, the proposed ZCS scheme can also realize zero-voltage-switching (ZVS) on secondary side rectifier to improve the overall efficiency further. With the nonzero pulsating dc output, the proposed ZCS scheme is effective even without an active clamp circuit, and it is suitable for applications where low-voltage dc to high-voltage three-phase ac power conversion is required.