Research On Bi-directional DC/DC Converter Of Hydroelectric Hybrid Vehicles

Hydroelectric hybrid vehicles have good economic value and social benefits in terms of reducing energy shortage,improving environmental pollution,promoting the development of environmentally friendly industries and technological innovation.Bi-directional DC / DC converter(BDC)is an important part of the research process of electric vehicles and hydrogen-electric hybrid vehicles.It serves as the carrier of voltage conversion and energy transmission which is between the low-voltage power battery and the high-voltage DC bus.It plays an important role of solving the problem that is voltage mismatch of the hybrid power system and it can save space and improve the stability of the power system.This paper selects the non-isolated Buck / Boost topology for the requirements of the hydrogen hybrid electric vehicle power system and BDC related technical indicators.In order to increase the response time of the BDC and reduce the system loss of the BDC and avoid the wrong conduction of the upper and lower arms of the BDC,the complementary control method of the switch tube is used for unified control.In view of the problems of large power tube stress and loss and reverse recovery of power tube parasitic diodes in BDC for hydrogen-electric hybrid vehicles,soft switching technology is used.In order to simplify the complexity of BDC modeling,an improved modified state averaging method is used to establish the analytical model of BDC.This method includes the forward power flow mode and the reverse power flow mode and can establish a small signal analytical model for both modes.In the forward power flow mode,the sudden change of the operating state of the load will cause the fluctuation of the high-voltage side bus voltage.In order to ensure the stable supply of the instantaneous power required by the load,it is necessary to control the stability of the value of the BDC high-voltage side.Therefore,double closed-loop control is adopted.The voltage control can enhance its stability and the current control can increase its response time.It can further improve the system’s regulation ability through the voltage and current feedback compensation network.In reverse power flow mode,the power battery needs to quickly absorb excess energy.In order to increase the operating efficiency under the reverse power flow mode and reduce the heating problem of the drive system,the closed-loop constant current control is adopted.The control algorithm uses dynamic PID and it selects different control coefficients according to the changes of system parameters to achieve the effect of dynamic optimal control.In order to ensure the stable driving of the BDC power tube,the driving chip and the driving resistor were selected and designed.In order to ensure the safe operation of BDC,the dual protection design of software and hardware is adopted in the circuit to ensure the safe operation of the system.The system control model is built by MATLAB / Simulink.The rationality of the scheme and the feasibility of the control strategy is verified through simulation waveforms and data.At the same time,a BDC prototype is developed,and the correctness of the scheme was verified by experimental waveforms and data under different conditions.Through the calculation and analysis of the experimental data of the forward and reverse power flow modes,it is concluded that the prototype efficiency has reached more than 94%.