The Study Of V2G On-board Charger For Electric Vehicle

V2G(Vehicle to Grid)is an interactive technology that uses electric vehicle as energy storage unit to realize energy exchange between grid and electric vehicle.Bidirectional charger is the device that charge electric vehicles and repay grid electric power.Compared with traditional charger,V2 G vehicle charger can realize two-way flow of electric energy so as to exchange energy between electric vehicle and grid,in order to repay energy to grid.Its performance is very important for the interaction and coordination between peak cutting and valley filling,spinning standby,voltage support and other services.Therefore,the vehicle charger with V2 G function has become a research hotpot of smart grid and electric vehicle.V2G mode charge and discharge reasonably between EV and grid,according to the charging and discharging characteristics of battery,on the premise of sinusoidal current on the grid side.At the same time,With the increase of charging power,better dynamic performance is needed to cope with in steady state.In this paper,the topological circuits of the front-stage bi-directional AC/DC converter and the back-stage bi-directional DC/DC converter are selected,and their working principles are analyzed and mathematically modeled.Moreover,the charging and discharging characteristics of lithium batteries and the equivalent circuit model are introduced.Secondly,solutions aiming at improving dynamic response of charger is studied.In terms of the disadvantages of slow dynamic response and complicated control parameters of the traditional direct power control algorithm of single-phase AC/DC converter,a kind of dead-beat predictive direct power control(P-DPC)algorithm based on the outer loop of capacitor energy storage is adopted to simplify the design of controller parameters and enhance anti-jamming ability through space vector PWM.The comparison of the simulation results shows that: the overshoot is reduced by 14.8%,and the adjustment time is reduced by100 ms,during the load disturbance,the overshoot is reduced by 100ms;during the load disturbance,the overshoot is reduced by 2.8% and the adjustment time is reduced by20ms;what is more,the total harmonic distortion rate(THD)of the line current is maintained at 1.65%,which indicates that the adopted algorithm has faster dynamic response and better anti-interference ability.Furthermore,in order to realize the three-stage charge and discharge control of the battery,this thesis theoretically analyzes the current single-closed loop,voltage and current double loop and voltage single closed-loop control applied in the lag DC/DC converter under different working conditions.Moreover,simulation results demonstrate the feasibility of the proposed algorithm.Finally,in this thesis,the simulations under various charging and discharging conditions of V2 G charger are carried out.The simulation results verify the feasibility of the algorithm in V2 G charger system.The experimental platform of a low-power back-stage bidirectional DC-DC converter of V2 G on-board charger is built in this paper.It is known that bidirectional DC/DC converter operates in Buck state,when a battery is charged.20 V DC voltage source is used to simulate the constant DC bus voltage,and electronic load is used to replace the battery load,which can obtain output voltage of 13 V with ripple coefficient of 0.7%;Because the bidirectional DC/DC converter works in Boost state when the battery is discharged,the output voltage of24 V ripple coefficient of 0.1% is obtained by replacing the slowly changing battery voltage on the input side with 10 V DC power supply.The experimental results proves the feasibility of the design.