Research On The Method Of Series Connected Batteries Charging

In recent years, the battery is being widely used in the fields of electric power, communication, transportation etc. In order to obtain higher output voltage, these single batteries usually need to be used in series. Due to limitations of the production process and the phenomena of overcharge and over-discharge, in the process of using them, there will be inconsistencies in capacity, voltage, resistance and other problems between the batteries, resulting in reduced efficiency, shortened life expectancy and even lead to security problems. Therefore, for the lithium iron phosphate battery pack, the study on the efficiently design for the battery balanced system has great practical value.Firstly, this paper analyzes the internal structure and chemical reaction mechanism of lithium iron phosphate at home and abroad, and analyzes the voltage, resistance, SOC and some other important factors of power of the battery in-depth. Then study the causes of inconsistencies of cell characteristics, and the necessity of balanced charge of a battery pack is proposed based on this. The various existing equalization method is comparative analyzed in-depth such as constant current charging method, constant voltage charging, pulse charging method, variable intermittent current charging method, etc., and sum up the advantages and disadvantages of traditional charging methods. Best acceptance curve charging method is proposed, and the advantages of this method is analyzed in theory.On the bases of analyzing and researching the various battery models, The PNGV equivalent circuit model is selected. We identify the model parameters through experiments, and establish simulation model of battery voltage in Matlab, in the end verify the accuracy of the model. Based on the analysis of existing SOC estimation method, and in view of the current electric car research status quo of electric vehicles' SOC estimation route, we propose a method to estimate SOC by combining ideas of Ah integral method, open circuit voltage and Extended Kalman Filtering, and based on PNGV equivalent circuit model we estimate SOC accurately. In the end, we simulate it in Matlab, the results show that the SOC estimation method has good accuracy.Finally, we design the hardware for the battery rapid balanced system and then carry out experimental test. Form the balanced overall system architecture, we make a thorough analysis. For the P89LPC935 microcontroller, we design a hardware for the balanced system. For the series of lithium iron phosphate battery, we make a experiment test, the result show that the actual work are consistent with the theoretical analysis, verifying that the feasibility of the balanced system and the efficiency of the balanced charging method.