Research On Electric Vehicle Bidirectional Charger And Battery Management System

The Chinese government gives subsidies on plug-in hybrid vehicles and pure electric vehicles(Evs),greatly promoting the development of electric vehicles,and making the electric vehicle charger and battery management system(BMS)become a research hotspot.With the large-scale application of electric vehicles and access to power grids,electric vehicle charger's influence on the power grid cannot be ignored,and the development of smart grid has put forward higher requirements for electric cars.And the electric vehicle charger,on the one hand,need to achieve bidirectional energy flow,that is,to meet with the V2G(Vehicle to Grid)applications,and provide energy to the grid;on the other hand,it should also provide reactive power compensation to the grid to support the grid.Therefore,the use of electric vehicle's bidirectional charger(EVBC)can promote the development of smart grid.In this paper,according to the V2G application requirements,bidirectional charger converter of electric vehicle and battery management system,and the common-mode leakage current suppression method of EVBC converter for the application of V2G are studied.The non-isolated two-stage circuit is adopted in the on-board EVBC converter circuit,composed of bidirectional AC/DC circuit and bidirectional DC/DC circuit.The bidirectional DC/DC converter uses 3 parallel Buck-Boost circuits to reduce the input and output current/voltage ripple of the battery side,thus enhancing the battery life and improving the power density;the bidirectional AC/DC converter uses H4 full bridge circuit to achieve the function of rectification and inverter.In this paper,the instantaneous power control strategy is presented for the single-phase Evs bidirectional charger circuit to realize the active and reactive power required for power grid dispatching.Aiming at the low-frequency common-mode leakage current,an active suppression method based on bidirectional DC/DC circuit is presented to suppress the low-frequency common-mode voltage of the single-phase EVBC DC link,thus improving the reliability of the charger.For the single-phase EVBC,the virtual quadrature component method based on the second-order generalized integral is used to realize the calculation of instantaneous power and phase-locked control(PLL).The battery management system in this paper adopts the distributed design,including a main control board and multiple data acquisition boards.The chip bq76PL455 from TI's company for battery management is selected and served as the acquisition board,and the ARM chip TMS570LS0432 from TI's company is selected and served as the main control board.The acquisition board is mainly responsible for collecting the voltage and the temperature data of single battery,and then sends them to the main control board by the means of communication.And the main control board analyzes and processes the data from the data acquisition board,including the calculation of the state of charge(SOC),state of power(SOP),the measurement of insulation impedance,and equalizing management and control of battery voltage.It can also communicate with the host computer and other control devices on the vehicle;The SOC estimation method used in this paper is the combination of AH integration and open circuit voltage(OCV),and correction work is realized through open circuit voltage in this method,finally,a relatively more accurate method of AH integration is used to estimate SOC,thus improving the accuracy of SOC estimation of the battery management system;Additionally,the measurement method of resistance bridge is put forward for insulation resistance of the battery.The bidirectional charger of 3.3kW for electric vehicle is developed in this paper,including bidirectional AC/DC circuit,the design method of power inductor and filter capacitor in bidirectional DC/DC circuit,and the selection of the main power switch device.The control strategy is simulated by PSIM,and the feasibility of the design of power circuit and control strategy are verified by experiments.And also the key algorithm in BMS system is verified by simulation and experiment.