Research On Control Strategy Of Converter System For Electric Vehicle

High efficiency output is essential for the safety and stability of electric vehicles,there is a wide range of fluctuations in the vehicle power battery when the vehicle is running,in addition,the voltage range of the vehicle power battery is limited,and the vehicle power battery cannot supply enough and stable voltage to make the motor running in the best working state to output the changing power demand quickly.The addition of a DC/DC converter system between the vehicle power battery and the motor system is a good solution to the problem,For DC/DC converter system,it is necessary to output high precision steady state voltage in the condition of large variation of input voltage and load change.It is very important to study the control strategy of DC/DC converter system to meet the above requirements.Considering the buck converter and boost converter is the typical nonlinear system.Commonly used in the car is a cascade of DC/DC converter system,which will greatly increase the degree of nonlinearity.Traditional linear control methods are not suitable for nonlinear system,directly applied to the buck converter and boost converter are cannot obtain ideal results,not to mention the cascaded DC/DC converter system.In recent years,many scholars have studied the global linearization of nonlinear systems by using the theory of differential geometry,combined with optimal control method;the control problem of nonlinear systems is studied.Firstly,the nonlinear mathematical model of buck converter and boost converter is established,then,combined with sliding mode algorithm,the control algorithm of cascaded DC/DC converter system is studied:(1)The realization of the control strategy of two basic DC/DC ConvertersFirstly,the state space method is used to represent the nonlinear mathematical model of two kinds of DC/DC converters,Linearization of affine nonlinear systems by using the method of differential geometry,A fully controllable linear system is obtained,Combined sliding mode algorithm with exponential reaching law,the control input of linear systems is designed,to reduce the chattering phenomenon.Per the relationship between linear input control and the input of the original system,get the control input of nonlinear system.The whole system and control algorithm are all set up in MATLAB/Simulink,three sets of test experiments are designed for the two basic DC/DC converters,namely,the periodic variation of the power supply voltage,the periodic disturbance of the load resistance,and the disturbance of the desired voltage.A detailed analysis of the simulation results,obtained in this control algorithm,the DC/DC converter with fast response speed,high precision,anti-load disturbance,power disturbance ability,strong ability to track the desired voltage,fully meet the system requirements.(2)The implementation of control strategies for two kinds of cascaded DC/DC ConvertersTwo cascaded DC/DC converters are designed,Buck-Buck cascaded DC/DC buck converter system,Boost-Boost cascade boost DC/DC converter system,based on the stability criterion of the forbidden zone,the parameters of the two systems are established,similarly,three sets of simulation experiments are designed for the two cascaded DC/DC converter systems.The simulation results show that the cascaded DC/DC converter system is stable,and the output voltage of the load converter fully meets the design requirements of the vehicle.