An Integrated Four Switch Buck-Boost Plus DAB Cascaded Converter And Control Strategy

In new energy electric vehicles,fuel vehicles and DC microgrids,Dual Active Bridge converters(DAB)are widely used due to the few components,galvanic isolation and bidirectional power flow.However,because the voltage of the battery or the super capacitor varies in a wide range,the ZVS range of the DAB converters are narrowed and the current stress are increased.Meanwhile,the voltage polarity reversal and voltage drop will occur during the dead time.To solve the issues of the traditional DAB converters in wide input voltage range,an integrated four-switch Buck-Boost plus DAB cascaded converters are proposed in this paper.The cascaded converters are composed of the FSBB converter and the DAB converter.The number of switches is reduced through the shared bridge.On this basis,a Dual-Edge PWM+Single-Phase-Shift control strategy is proposed.Since the FSBB converter converts a wide input voltage into a constant voltage as the input of the DAB converter,the DAB converter can eliminate the dead time effect.Firstly,the control strategy of the FSBB converter and the DAB converter is analyzed in this paper.The cascaded converters have four working modes in the forward and reverse stage,and the ten working modes under the boost working mode in the forward phase are described in detail.After that,the dead time effect of the DAB converter is analyzed.Secondly,the ZVS range of the shared bridge and the other bridges of DAB converters are analyzed.The intermediate voltage affects the ripple value of the inductor current of FSBB converters and the intermediate voltage is optimized.In order to improve the efficiency of the DAB converter under light load,a two-mode control strategy is proposed.When the output power exceeds the threshold,the voltage transfer ratio is maintained at unity,and when the output power is lower than the threshold,the voltage transfer ratio is setted slightly greater than unity.Finally,the normal work waveforms and control strategy of the cascaded converters are verified through the simulation of Saber and Matlab.A protype is built with input voltage 175-320 V,out voltage 24V/21 A.Experimental results prove that the proposed converters can deal with the issues of the traditional DAB converters in a wide input voltage range.Meanwhile,the cascaded converters converters have advantages of few components and high efficiency.