Research On V2G Converter For Electric Vehicles And Its Control Strategy

With the popularization of Electric Vehicles and the development of Smart Grid,V2G technology for EV has attracted continuously attention from both industrial and academic circles,consequently V2G has also become a hotspot for domestic and foreign scholars.Being regarded as removable energy storage units,the power battery packs of EV could be controlled to charge or discharge power to grid by using power electronic converter of V2G technology,and the bidirectional energy flow between grid and EV's battery is achieved.Thus V2G technology has a positive influence in terms of peak load shifting of grid,cost saving of EV's owner,and benign interconnection and interaction between EV and grid.The key foundation of realizing V2G lies in the V2G converter which is capable of controlling bidirectional power flow.In this thesis,a V2G bidirectional power converter is designed.Two stage topology is chosen,three phase full bridge voltage source PWM converter as preceding AC-DC and dual active bridge converter as succeeding DC-DC.The analysis of working principle and mathematical model indicates that this topology is able to fullfil four-quadrant operation of AC and charging or discharging of battery.In order to meet three operation mode required by V2G founction,the overall control schematic diagram of converter is proposed and following studies of detailed control strategies for two stage are narrated in this thesis.When power flows forward to charge battery,voltage and current double close-loop based on direct current feedback is adopted for AC-DC converter to control DC voltage and AC current,and single phase shift control combining voltage and current close-loop is adopted for DC-DC converter to realize constant current-constant voltage charging.When power flows backward to discharge battery,current close-loop controlling AC current is employed for AC-DC,and voltage close-loop acquiring phase shift angel is employed to stabilize output voltage.When operated at reactive power mode,the reference reactive current of current close-loop of AC-DC is obtained from Q control.The simulations of the V2G converter and the control strategy carried out with advanced generic battery model verify that it can control the transmission of bidiectioal active power for charging and discharging as well as bidirectional reactive power.The possibility of participating in frequency/voltage regulation service for V2G converter is discussed in this thesis in consideration of its four-quadrant operation ability.Frequency/voltage regulation droop curve suitable for EV and V2G converter is studied,and then frequency/voltage regulation droop controller is designed correspondingly,which could adjust the active/recative power transmission of the converter according to frequency/voltage deviation and should be added respectively before the reference value of PQ control.The results of simulation model show that the V2G converter with its relevant frequency/voltage regulation droop control could respond to the variation of source frequency/voltage quickly and sensitively.As a result,the tramssion of its active/reactive power is adjusted to satisfy frequency/voltage regulation demands.At last,a low power hardware platform for experiment is built up.The work includes schematic and PCB design for main circuit,drive circuit and sampling and conditioning circuits,and software process programming for DSP control system.The experiment results demonstrate that the rectifier and inverter operation of AC-DC converter,and the output DC voltage and current stabilization of DC-DC converter could be all controlled.Therefore,the bidirectional active power transmission of two stage could be effectively controlled,enanbling it to charge or discharge battery.This thesis provides theoretical and technical supports for the research,popularization and application of V2G converter for EV to a certain extent.