Research On On-board Charging System Based-on Isolated Three-port Converter

In recent years,the depletion of non-renewable energy and the environmental pollution caused by carbon emissions have become increasingly severe.Therefore,the market development and technology research of the new energy industry have become increasingly hot in various countries.Electric vehicles,with their advantages of high efficiency and low emission,have attracted wide attention from the international community.The on-board charging system is the core of electric vehicle,which plays the role of energy conversion.However,because the high and low voltage charging modules in most vehicle charging systems are two separate parts,the equipment occupies a large space and the energy conversion efficiency is low.The power integration of the two parts can effectively solve the problem.In this paper,the traditional charging structure of electric vehicles is studied first,and the internal high-voltage power battery charging module and low-voltage battery charging module are compared and analyzed.A three-winding transformer is proposed to magnetically coupling the power grid input terminal,the high-voltage power battery terminal and the low-voltage battery terminal.The high and low voltage charging modules are combined to form an isolated three-port converter.The operation principle,operation mode and control strategy of the three-port converter are studied,and the dual diode bridgeless PFC converter and CLLC resonant converter are selected as the main circuit topology of the vehicle charging system.According to the design index,the parameters of the power components in the converter are designed.The voltage gain characteristics are analyzed by the fundamental wave analysis method.The transformer ratio and resonant cavity parameters are determined by the selection of inductance coefficient and quality factor.The corresponding control strategies are designed for the two operating modes of the vehicle-mounted charging system respectively.The transfer function of the controlled object is obtained by establishing the small signal model of the double-diode bridgeless PFC converter,and the double closed-loop control structure is designed.For the two output ports,the CLLC resonant converter uses the control method combining frequency conversion control and fixed frequency phase shift control respectively to adjust the frequency of the driving signal and the size of the external phase shift Angle to realize the voltage regulation of the high voltage power battery and the low voltage battery.Finally,the simulation model and experimental prototype were built,and the vehicle charging system was tested to obtain the relevant experimental waveform and efficiency curve.The simulation and experimental results verify the correctness of the theoretical analysis.