Analysis And Control Method For Isolated Three Port DC-DC Converter

Isolated three port DC-DC converter is a new type of DC-DC converter.The full bridge converter with each port of isolated three port DC-DC converter studied in this paper is connected to a winding of three-phase high frequency transformer.It can easily adjust the turn ratio of transformer winding to realize voltage matching of each port.The isolated three port DC-DC converter is compact in structure,and has natural high power characteristics and flexibility in control.It can be connected with multiple power sources and loads at the same time.In recent years,it has been widely studied and concerned in the fields of renewable energy generation system,hybrid vehicle,fuel cell vehicle and so on.This paper analyzes the working principle and working mode of isolated three port DCDC converter.Based on the power calculation of dual active bridge DC-DC converter,the power transmission expression of three port converter is derived.The method of small signal modeling of three port converter is studied by means of average current method.Because of th e cross coupling between the ports,the feedforward decoupling control of the isolated three port converter is needed.In order to remove the resonant peak of current flow control port,a virtual resistance is introduced to increase the damping of current control system by equivalent transformation of control block diagram of isolated three port converter.Based on the application of the isolated three-port converter in the fuel cell system,the paper introduces the characteristics of the fuel cell.Based on the small signal transfer function model of the isolated three-port converter system,it studies the use of a proportional integral(PI)controller and cooperates with it.The feedforward decoupling control method realizes the balanced control of the fuel cell,the output of the power supply,the load voltage and the power flow,and suppresses the mutual influence between the ports.The control system of three port converter is designed with the help of MATLAB control system design tool.In the design process of the control system,it is necessary to make proper trade-offs among the system gain,cross frequency and peak overshoot,rise time and stability time.Based on the above modeling and control system design,the fuel cell power generation system has the characteristics of uninterrupted power supply and good control performance.The isolated three port converter and its control system are simulated by Matlab/Simulink.