Design And Study Of Control System Of Dc Charger

The replacement of the fuel vehicles by the electric vehicles is an on-going trend.Chargers occupy an important position as an ancillary facilities,and the related research and development have attracted much attention.At present,various types of chargers are being researched and developed at home and abroad actively,covering from low-power AC and DC chargers to high-power DC chargers which is the mainstream development direction in recent years.In this paper,a 120 k W DC charger was designed,which has the problem that the output current of the power supply module was not uniform and the voltage information of the single battery can not be displayed in the charging process of the electric vehicle.The main research works in this paper is as follows:Firstly,the overall solution of the DC charger control system was designed.According to the functional requirements of the DC charger,a system hardware and software platform was built based on the embedded technology.The hardware mainly consists of the MK60DN512 microcontroller,the start/reset circuit,the JTAG download/debugging circuit,the clock circuit,the minimum system power supply,the output voltage sampling and the signal conversion circuit,the output current sampling and the signal conversion circuit,the AC relay control circuit and the temperature detection circuit.The controll software was developed based on the Keil MDK platform,and the library function development method was adopted.According to the function,the software was divided into three parts: the charging control module,the parallel current sharing module and the single-cell voltage acquisition module.Then,the overall architecture of the software was built.Secondly,the charging control module was designed.The charging control module mainly consists of the following parts: the battery management system,the power supply module,the controlling board,the CAN communication and the RS485 communication.The battery management system of the electric vehicle,the working principle and the technical parameters of power supply module were introduced.The CAN interface circuit and the RS485 interface circuit were designed.The communication protocol between the control board and the related two parts,including the power module and the battery management system(BMS),were analyzed.Finite state machine was used to solve the complex logic problems in the charging control process.And finally,the program of the charging control module was designed.Thirdly,the parallel current sharing module and the single-cell voltage acquisition module were designed.The traditional methods of parallel current sharing control wre analyzed.The three-loop control method based on an additional controller was used and verified by the simulation model built with the MATLAB.Then the program of the parallel current sharing control was designed.Based on the original program,the single cell voltage acquisition function was added.The voltage of the cell was obtained by reading and translating the CAN message.Finally,a test platform of the developed prototype was set up.The CAN communication was tested in the following procedures: the charging handshake,the configuration of charging parameters,the charging process,and the charging end process.The test of the cell voltage message was added based on the original program.After the simulated cell voltage message was sent via the CAN analyzer,the cell voltage displays normally via the serial port,indicating that the module function is normal.The highest and the lowest single cell voltage have a difference of 0.18 V,its over threshold 0.1V,indicating a mild deviation inconsistency among the battery pack.Finally,the parallel current sharing is tested.Without flow program,the limit value and the average value have a difference of 0.84 A.After flow program,the limit value and the average value have a difference of 0.26 A.Its current sharing accuracy is 3%,which meets the requirement of the GB standard(5%).