| Under the dual pressures of energy crisis and environmental protection, the new engery technology has been paid more and more attention and development. Among them, the battery, as an important storage device in new energy system, is widely used in electrical equipment. LiFePO4 batteries have been widely used in industrial and business, such as:space equipment, mobile phones and electric vehicles because of the high energy density, no memory effect, long life, low self-discharge rate and excellent charging and discharging performance.To meet the voltage and capacity requirements in electrical equipment, LiFePO4 batteries connected in series or parallel are often employed for many practical applicaitions. Because of the inevitable inconsistencies in the LiFePO4 battery, and with the battery charge and discharge repeatedly, this kind of inconsistency can be intensified, and reduce the available capacity of the battery, even affect the battery safety. Therefore, the battery management system is often used in practical power battery pack, in which the battery balance system as an important technical means to ease the inconsistencies of battery is the most important pary of the battery management system.At present, the common method of battery equalization is consuming the excess energy in the battery or transferring to other cells, known as passive and active balancing. Passive balancing is mainly used in small power or less quantity battery system, the excess energy is consuming with the form of heat through the external resistor to reach the balancing purpose. Active balancing is transferring the excess energy among the batteries to reach the dynamic balance and the maximum use in the battery. Compared with the passive balancing, the active balancing can significantly increase balancing speed and reduce loss with capacitance or inductance as energy transfer element in external circuit.This paper is based on the deep water power LiFePO4 battery project in Temasek Polytechnic Clean Energy Reseach Cnter, Singapore, and the balancing speed, efficiency and components number are considering in comparison. Two optimized balancing topologies are presented on the foundation of the extensive application of Buck-Boost circuit. The battery combined Buck-Boost balancing circuit optimizes the defect which the enegy can only be transferred in the adjacent cell, reducing the steps in energy transfer process and increasing the balancing current, thereby improving the balancing speed; The switched inductor Buck-Boost balancing circuit is use inductance modules substitute for inductors in tranditional balancing circuit can achieve arbitrary battery energy transfer, not only reduced the number of power switches in balancing system, and improve the balancing speed and efficiency.For balancing control algorithm, the paper points out the existing problems of SOC-based balance, voltage-based balance and capacity-based balance, which combined with the charging and discharging characteristics under certain conditions of LiFePO4 battery. Then, we put forward a hybrid battery equalization control algorithm.In order to verify the above proposed balancing topology and control algorithm, the different topologies and algorithms are respectively applied in deep-sea power battery and electric vehicles. The experiment shows the difference between different balancing topologies and control algorithms, which could choose the most suitable equilibrium criterion at different stages of the battery to improve the effectiveness and accuracy of the balancing system. |
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