Research For Lithium Iron Phosphate Battery Charging Method And Design For Equalization Charging Module

Power battery is the core energy of Electric Vehicle. Lithium iron phosphate battery is the best choice of power battery because of its high security, power, environmental protection and long life. However, the research on charging methods of lithium iron phosphate battery is just starting up and there are still many unresolved problems in engineering application of Electric Vehicle.In this background, following work has been completed:A charging experimental platform has been built based on the charging requirements of Lithium iron phosphate batteries. Relative CAN networks and monitoring unit also have been designed. Main control panel of monitoring unit communicates with both charger and battery management system through the CAN networks. It controls charging methods of charger and uses serial interface to complete the communication with upper computer.The charging characteristics and mechanisms of lithium iron phosphate battery have been analyzed, and a large number of charging experiments on a single cell and series of lithium iron phosphate battery have been completed. Based on these experiment results, a charging method about which the single cell upper limit voltage is constant based on fuzzy control has been proposed. The method can conduct overcharge protection on each single battery.Taking into account of a single cell in the series charging, the inconsistency among batteries will gradually increase. In order to ensure the life of batteries, only reduce utilization of batteries. Equalization charging, as an effective way to reduce the inconsistency of batteries, balances the characteristics of batteries, thereby improving utilization of battery and significantly extends battery life. After analyzed many schemes about Equalization charging,a balance scheme which first charging with the main charger, and then charging with a equalization charging module has been proposed.The main circuit, control circuit and the software module of equalization charging module has been designed. A test circuit also has been built, the experimental waveforms of equalization charging module in the experimental circuit have been given. Based on the experimental circuit, a experiment of charging a not being fully charged cell of batteries has been completed, which demonstrated the feasibility of this scheme.