Research On Balancing Circuit Of Series Battery Stack And Battery Management System Design

With the rise of the national electric vehicle industry,power battery as energy sources for electric vehicles has developed rapidly.In order to achieve the voltage level required by electric vehicles,power battery usually need to be used in series.Because of the differences in the self-parameters and working environment of each cell in the battery stack,the voltage inconsistency between the cells gradually increases during actual use.The overall performance of the battery stack is degraded,so the balancing circuit,what can reduce the voltage difference between the cells online,has become a research hotspot.In this paper,the balancing circuits are studied in depth,and the balancing circuit optimization method based on voltage equalization target is proposed.Based on this,a battery management system integrating battery stack balancing,detection,control and protection is designed and fabricated.Firstly,the operational principle of the voltage-double rectification balancing circuit is studied.Aiming at the problem that the balancing path length and only half of the alternating current participate in the balancing,resulting in lower efficiency and lower speed.Based on the idea of increasing the balancing current path,isolated bridge rectification balancing circuit is proposed to improve balancing efficiency and speed.The operational principle and working characteristics of isolated bridge rectification balancing circuit were analyzed in detail,and the simulation and experimental verification were carried out.The research results show that the isolated bridge rectification balancing circuit inherits the advantages of independent voltage balancing,small number of magnetic components and switching tubes in voltage-double rectification balancing circuit,and solves the problems of the voltage-double rectification balancing circuit,which improves the equalization efficiency and equalization speed.As well as,both switching tubes can achieve Zero Voltage Switching(ZVS),which reduces switching losses.Through research,it is found that when considering the series resistance of the diode and the Equivalent Series Resistance(ESR)of the capacitor,the isolated bridge rectification balancing circuit will have current overlap under the small cells’ voltage difference,so that balance efficiency is reduced.Aiming at this problem,this paper adds a switching resistor balancing circuit based on isolated bridge rectification balancing circuit,proposes a hybrid balancing circuit,and studied the corresponding balancing strategy to improve the efficiency.Finally,simulation and experimental verification were carried out.The research results show that the hybrid balancing circuit can effectively solve the problem that isolated bridge rectification balancing circuit reduces balancing efficiency due to current overlap,and further improves the balancing efficiency of the circuit.In order to ensure the efficient,safe and reliable operation of the series battery stack,a centralized battery management system based on hybrid balancing circuit is designed by combining the analog front-end chip Bq76930 and the microcontroller STM32F103C8T6.The hardware circuit design and software writing were completed,and the experimental platform was built.The charging and discharging control,the balancing control experiment and the data acquisition experiments of voltage,temperature and current were carried out.The experimental results show that the battery management system has good running performance.