Design And Implementation Of High Frequency PFC On-board Charger

With today’s environmental problems and energy problem increasing, the electric vehicle has became the effective way to solve the above problems, because it has no pollution and uses secondary clean energy. For electric vehicles to provide the source of power, the charging of battery has been restricted the development of the industry. At present, at home and abroad the development of constant current and constant voltage charging, including two stage forms and three stage forms, is the most widely. Therefore, designing the on-board charger, which conforms to the battery charging curve, can effectively improve the electric car endurance ability. The purpose of this research is to design a small volume, light weight, power for4kw, high PF value and high efficient on-board charger. And the battery management system can monitor the battery charging status in real time.On-board charger in essence is a kind of high frequency switching power supply, according to the desgn principle of switch power supply, this paper has achieved the high-frequency on-board charger, that conforms to the lithium battery charging curve, this topic has done the main works as follows:(1) According to the charger design parameters required, the system structure of charger is determined. The4KW charger is designed as two parallel of2KW monomer chargers by way of distributed power supply. The paper puts forward in the key technology and solution in designment of monomer charger. And the current sharing problem of the whole machine, the paper adopts the cascade technology to work out it.(2) The paper has conformed the main circuit topology structure according to working principle of DCDC converter, and then designs the high-frequency transformer corresponding the selected topology structure, and the rectifier filter components, and increases the "soft start" circuit in order to improve the safety of the charger.(3) The paper has simulated the charger control system of PFC (power factor correction), soft switch technology, and so on, in order to verify the technical rationality of circuit designment, that’s as the reference for the part of the circuit designment. Aimed at the problems existed in the simulation results, the circuit improvement ideas have been proposed. Through the comparison and analysis of many PFC main control chips and kinds of PWM control chips, the paper has designed circuit of control system of charger in detail.(4) According to the selected MCU master control chip, the paper has programmed to implement the CAN communication between BMS (battery management system), the stability of charger output and the improvement of the protection function, and the drawing of different charging curve.(5) This paper has completed the design of the on-board charger, and has tested the modules function of the charger, single charger performance, and parallel charger performances through a series of experiments.The results show that the charger works steadily in the rated power of the efficiency value more than90%, the PF value as high as99.1%, and two monomer chargers uneven flow degree is less than5%, and realizing different charge modes includeing constant voltage, constant current and so on, that according with the charger design requirements.