Research On Optimal Control For Dynamic Process Of Buck-IPT System Based On State-trajectory

In recent years,with enhancement of people's awareness of environmental protection,electric vehicle gradually replaced fuel vehicle as an irresistible trend of social development.Inductive power transfer technology make the charging process of electric vehicle more flexible,safe and tidy.It avoids manual operation of charging gun and improves the automation level of system.Therefore,wireless charging is an ideal charging way for electric vehicles.The research object of this paper is Buck-IPT system,which is the typical topology that electric vehicle charging system adopts.High order and nonlinearity make the whole system difficult to control.Dynamic process is especially critical for safe and stable operation of system.State-trajectory technique can visualize the trajectory motion of system state variables intuitively in state plane.It is helpful to analyze the characteristics of system dynamic response and to design the trajectory of system motion.The dynamic response of existing system is slow,starting process is time-consuming,and voltage and current are overshoot.Aiming at solving these problems,dynamic response is optimized by using control technology based on state-trajectory planning.The main contents of this paper are as follows:As the main circuit to regulate power of system,Buck converter plays an important role in the dynamic process.Therefore,this paper takes the typical second order Buck circuit as research object firstly,preliminarily analyzes its state-trajectory equation,discusses how to determine the optimal switch point,and combining with sliding mode control to make the system steady as soon as possible.Aiming at load switching problem,an intercept compensation algorithm is proposed to make the output voltage return to steady state quickly and remain unchanged.On this basis,IPT system is regarded as the load of Buck circuit.The secondary side circuit is reducted to primary side,and the equivalent circuit model of Buck-IPT system with a controlled current source is established.In order to get the trajectory equation of system,it is further simplified to third order equivalent average circuit model,and method of finding the optimal switch point is studied.On the state plane of capacitor voltage and inductor current,a sliding mode control method based on state-trajectory planning is used to optimize the dynamic process of system,and how to limit inductor current overshoot is studied.On the state plane of capacitor voltage and capacitor current,a method of going into the steady state by multiple switch acitons is used to optimize the dynamic process of system,which avoids detecting capacitor current,and the effect of dealing with load disturbance is better.After the output of Buck circuit is stable,the whole system has not yet entered the real steady state.In this paper,a concept of control switching process is put forward and the solution is given: PID control is applied to secondary side output to achieve constant voltage or constant current state,and current sharing control is applied to interleaved buck circuit.After that,the software module and flow chart are given,and some hardware circuits are analyzed.Finally,in order to verify feasibility and effectiveness of the control algorithm described in this paper,MATLAB software is used to simulate,an actual circuit is built for experiments.Finally,simulation and experiment results are analyzed.