In practical applications, due to the differences between lithium battery cells, after a period of charging and discharging, it is found that the upper and lower limit voltages of each single battery are uneven, which seriously affects the performance of the system. In view of this situation, the concepts of upper balance and lower balance are proposed, and then the upper and lower balance circuits of lithium batteries are deeply studied. The experimental results prove that the correctness of several lithium battery equalization circuit designs has laid a solid foundation for the study of high-performance hybrid power systems.

　　Ni-MH batteries are alkaline batteries. Due to the relatively low cell voltage and the "memory effect", regular large-scale discharge is necessary, which greatly increases the task of the power management system. Secondly, it also has the shortcoming of high self-discharge rate (10%~15%).

　　Compared with other batteries, lithium-ion batteries have high power density (800W/Kg), high cell voltage (average voltage of 3.6V), no pollution to the environment, and low self-discharge rate (about 3% to 5%). The "memory effect" and other characteristics are an ideal power battery, so it is widely used in mobile power supplies, hybrid vehicles, backup power supplies in medium and low voltage switch cabinets, and aerospace flight energy storage devices.

　　1. Defects of existing domestic lithium battery protection circuits

　　The average voltage of lithium battery cells is only 3.6V, and the discharge current also has certain requirements. In order to improve the current and voltage levels of the system, in some dynamic occasions, a high-current and high-voltage lithium battery pack is generally used in parallel and then connected in series to form an energy system. Since lithium batteries are very sensitive to voltage, a certain protection circuit is generally added when the battery pack is in use.

　　2, the principle of improved lithium battery protection circuit

　　Equalization circuit refers to a hardware circuit that is artificially added. It can maintain consistency between the upper limit voltage of the cell or the lower limit voltage of the entire battery pack, thereby effectively protecting the upper limit charging voltage and the lower limit discharging voltage of the battery, and fundamentally Reduce the impact of the battery on the system, so as to achieve the purpose of improving battery performance and extending battery life. It includes two circuits of upper equalization and lower equalization.