Design Of Active Balancing Control System For Lithium Battery Pack

In the situation of increasingly tense energy and environmental problems, and the widespread application of lithium power battery energy storage system has become an important direction of the new energy development now. The solution of Lithium-ion battery as a power source of new energy electric vehicles are acclaimed, but the inconsistency problem of cells is a big problem which hinder its promotion in the application. Currently, the use of balance control technology to build lithium-ion battery balancing system is one of the important ways to improve the inconsistency of battery pack.Firstly, the causes and solutions of inconsistency of lithium-ion battery pack were analyzed, pointing out inconsistencies in reducing the battery pack in the course of the importance of a balanced system. Respectively from the battery capacity, battery voltage, state of charged a total of three aspects analyzes the manifestation of the battery pack inconsistencies, select the state of charge as a balancing variable. Then on the advantages and disadvantages of common equalization circuit topological structure were analyzed, select the active balance based flyback converter topology, and the basic parameters of the flyback transformer is calculated.On this basis, the paper proposed and designed the active balance control system based on bidirectional flyback converter. The system uses high-performance microprocessor STM32F103 as a main control unit, When the battery pack is charged or discharged, active equalization system available through the CAN bus battery management system calculated balance information, controlling logic matrix switch to select the cells to be balanced, the use of PID to control algorithm to calculate the optimal value of the PWM control bidirectional flyback converter topology to achieve the target unit’s battery charged and discharged. After complete equilibrium into hibernation, the system will wait for balancing action wake again. Logic matrix switch realize the expansion of the I/O port, by using 74HC595 and 74HC138, the system achieves closed-loop calibration to ensure the accuracy and trouble-free relay switching occurs by using 74LS165. By extending the backend switch logic matrix, the system can be easily applied to the different quantity and different voltage grade lithium battery module. It has good prospects for development.The experimental test results show that the solution has advantages of fast balanced speed, higher efficiency, can realize real-time and effective active balancing effect.