Design Of Isolated Bidirectional DC-DC Converter Based On Model Predictive Control

The application of bidirectional DC-DC converter in renewable energy power generation,energy management of electric vehicles,space power supply and other systems has received extensive attention.The bi-directional isolated bi-directional DC-DC converter studied in this paper has a symmetrical topology.Through the corresponding control,the zero-voltage switching of the switch can be realized.At the same time,energy can flow bidirectionally,thus building energy exchange bridge between energy storage unit and DC bus.In this paper,a new control strategy for isolated bidirectional DC-DC converter is proposed to improve the dynamic characteristics of voltage and current in boost mode and buck mode,and to improve the stability of the system.In order to realize the energy flow on both sides of the bidirectional converter,a new modulation mode is proposed,which adopts Bipolar-Phase-shifted modulation mode,bipolar modulation in boost mode and phase shift modulation in step-down mode.Then,a predictive model is established to predict the corresponding objective function value of the possible state of the next stage switch,and the objective function is established according to the control performance.The switch state of the next stage of the converter is determined according to the objective function value,so as to optimize the control effect.Finally,a hardware experimental platform of 5 kW isolated bidirectional DC-DC converter is built for experimental verification.Firstly,the principle of isolated bidirectional DC-DC converter with the new modulation is studied.Bipolar modulation is used in boost mode and phase shift modulation is used in stepdown mode.Then,the working state and theoretical waveform of the converter under two modes are analyzed,and a simulation model is built in Simulink to verify it.In order to design the closed-loop control system for the converter,a small signal model of DC-DC converter is established in this paper.Two factors affecting output voltage ripple are summarized:closed-loop control and input voltage ripple.Then the model predictive control strategy is introduced and a control strategy with fast dynamic response and good stability is proposed.It is applied to isolated bidirectional DC-DC converter,and then a simulation model is built in Simulink to verify it.In this paper,a 5kW experimental platform is made,and corresponding software programs and hardware circuits are developed.Software programs include:main program,model predictive control algorithm,ADC sampling program,communication program,etc.Hardware circuits include:converter main circuit,IGBT driving circuit,double closed-loop single-ended flyback power supply circuit,MC9S12XF128 control system circuit and sampling signal conditioning circuit.Based on the experimental results,the DC bus voltage of the model predictive control system has good dynamic performance and stability.