Research On Naturally Clamped CF-DAB Composite Converter

With the concept of sustainable development gaining popularity,renewable energy power generation technology has become a hot research topic in the industry.Fuel cells have the advantages of wide fuel,less harmful gas emissions,and high energy conversion rate,and therefore it becomes an important part of renewable energy power generation.As a power electronic module connecting the fuel cell and the high-voltage DC bus,it is necessary to not only match the corresponding voltage specifications,but also consider the battery life.The current-fed DC/DC converter has inherent advantages such as low input current ripple,short-circuit protection,and high step-up ratio,so it is suitable for such low-voltage and high-current applications.In order to solve the problems of the high current stress,voltage spikes during the off period of the low-voltage side switch devices,and limited soft switching range of the traditional current-fed DC/DC converter,a natural clamped CF-DAB(Current-fed Dual Active Bridge)composite converter has been proposed.The problems of traditional current-fed DC/DC converters are solved by changing the topology.According to the proposed topology,a corresponding phase-shift modulation is proposed.And on the basis of the proposed topology,four working modes are proposed,i.e.,full mode,composite mode,full-bridge mode and half-bridge mode.According to the voltage gain and the transmission power range,the working intervals of the four working modes of the proposed composite converter are divided.The multi-mode working mode brings more flexibility and stability to the proposed composite converter.The voltage spike phenomenon of the low-voltage switch device is solved by the modulation of the high-voltage side.The change of voltage gain and transmission power of the proposed composite converter and the reduction of internal circulating current are achieved by adjusting the duty ratio of the low voltage side and phase shift angle.Under the premise that the proposed composite converter has the advantages of wide input,wide output and low circulating current,the soft switching in the full load range is still guaranteed.Based on the steady-state operating waveform,the proposed natural clamped CF-DAB composite converter is theoretically analyzed,and expressions such as leakage current,low-side switch device current,voltage gain,and transmission power are derived.Compared with the traditional current-fed DC/DC converter,the advantages of the composite converter are fully illustrated by the comparison of the number of components,transformer turns ratio,voltage and current stress and soft switching characteristics.The circuit parameters of the proposed composite converter are designed under rated conditions,the correctness of theoretical analysis is verified by PSIM 9.1.4 simulation software,and an experimental prototype is built to further verify the feasibility of the proposed topology.