Research On Bi-directional Flyback Converters

This paper studies on bi-directional flyback converters which are applied to low power applications. It analyses operational principle and characteristics of bi-directional flyback converter, concludes snubbers of its leakage inductor energy and soft-switch techniques, and applied it to low capacity lead acid batteries for Electric-Vehicles. Two prototypes are designed. An active clamp bi-directional flyback controlled by single closed loop is proposed.In chapter one, the principle and application of Bi-directional DC-DC Converters (BDC) are introduced. The present status of BDC, including topologies, soft-switching techniques, and control methods is reviewed.In chapter two, overall researches have been done on focus on bi-directional flyback converter, including its operation principle and topology characteristic. According to its features, the snubbers of leakage inductor energy and soft-switch techniques are explained. At last, small signal model are established when the converter works at continuous current mode, and conditional control method is explained.In chapter three, a bi-directional flyback converter used RCD snubber and Quasi-resonant soft-switch technique is applied to positive-negative charging technology. At first, positive-negative charging technology is explained. The charging object and charging parameters are list. Then a no-dissipation positive-negative charger is designed according to the parameters. Experimental results are shown at last.In chapter four, active clamp bi-directional flyback converter is applied to positive-negative charging technology. At first, principle of active clamp bi-directional flyback converter is analyzed. The circuit modeling is deduced with average switching network method. Based on simulation, the transfer functions from control to output are single pole during low frequency range in both positive and negative operation mode. The close loop control can be realized with same compensator. The parameters of the compensator are designed. Simulative operation waveforms and experimental prototype results are shown at last.Conclusion is given in the last chapter. In the application of no-dissipation positive-negative charging technology, active clamp bi-directional flyback converter realizes close coop control for both energy transfer direction. It is the optimal BDC in low power applications with simple control and high efficiency.