Research On Active Inductance Balancing For Series Lithium-ion Batteries

As in the advantages of energy density, life, self-discharge rate and security, lithium-ion battery is becoming the preferred energy storage battery, and it is widely used in portable equipment and new energy vehicles. To meet the requirements of high-power, multi-batteries need to connect in series to provide energy. Due to the differences in voltage, capacity, internal resistance in the process of battery production, the initial differences are getting further expansion with ignoring the differences. The specific performance is that li-ion batteries reach cut-off voltage much earlier and the single battery’s life decreases rapidly. At present, it is an effective way to ameliorate batteries’inconsistency by establishing lithium-ion battery equalization system in the use of balance control technology.Based on research status at home and abroad in batteries’balanced circuit topology and control strategy, this paper focus on designing active inductance balancing system for series lithium-ion batteries, combined with the characteristics of charge and discharge for the li-ion battery. The whole system is designed to improve batteries’imbalance, optimize performance, increase the number of cycle and extend batteries’life. The equalization system is projected in a distributed balance, master-slave topology. ATA6870 is selected as slave controller to collect the front voltage and temperature, the host MSP430F149 is designed as the host controller to carry on data processing via SPI communication, carrying out balanced control strategy. Equalization circuit combines active inductance and flyback balance to a loop topology, ensuring the ring flow of energy. The host controller drives MOSFET to control batteries’charging and discharging.PSIM is selected as simulation platform in this paper, the balancing topology of active inductance, flyback converter and overall balance are analyzed respectively, which verifies the feasibility of circuit topology and parameter design. On the basis of hardware, software control system is programmed in the thesis, master and slave controller’registers and SPI communications are configured, balance control strategy is modified to achieve equalization at the same time. Experiment PCB is soldering and test platform is built at the end of paper. Active inductance, flyback converter and overall balance are validated respectively. The results show that series lithium-ion batteries could realize the goal that the maximum voltage difference is less than 0.1V and overall charge-discharging can be controlled after using active inductive balance system. The balance system’s control is stable, simple and feasible, it is greatly significant to improve pack’s unconsistency and increase batteries’life.