Research On Current-fed Bidirectional DC-DC Converter

Transportation electrification has received significant interest by researchers and industries for next generation vehicles as it offers merits of low emission,reduced noise,smooth drive,better efficiency and high performance.Bidirectional DC-DC converter plays an important role interfacing fuel cell bus and traction inverter and energy storage.Generally,lower input current ripple,high step-up ratio,dc input current controllability and efficient operation over a wide input range are required by the energy storage.Current-fed converter is a good alternative compared to voltage-fed converter for applications such as fuel cells.However,the current-fed dual active bridge bidirectional DC-DC converter with the conventional phase shift modulation is not perfect due to the following reasons: high peak current and high circuiting current at light load,and high voltage stress of switching devices in the high voltage side.Hence,the topology and control strategy are studied in the paper,which is significant for improving the reliability and efficiency of converters.To improve the performance of the converter at light loads,the dual phase shift modulation is applied to actively control the peak current.The control variables are chosen such that the excess current is just enough to achieve zero current soft-switching(ZCS)turn-off of the LV devices.At the same time,a bidirectional three level DC-DC converter for high voltage applications is chosen to reduce the voltage stress of switching devices.Current-fed half bridge topology is adopted in the LVS and three-level half bridge topology is used in the HVS.Then the article analyzes the working principle of the high frequency isolated dual active full-bridge converter and full-bridge plus three-level converter in detail,which are controlled by phase shift modulation and dual phase shift modulation respectively.Besides,the characteristics of the converter under two modulations are compared,including the current,voltage and soft switching range.PSIM simulations and experiments are made to verify the working principle.A 1k W lab prototype is built.Experimental results show that,bidirectional threelevel DC-DC converter can achieve voltage sharing of switching devices in the HVS and reduce the voltage stress to half.Dual phase shift modulation can control the peak current and increase working efficiency of the converter.Furthermore,all the switching devices can achieve soft switching.