| With the rapid development of the world's automobile industry, the supply of petroleum is running out fast day by day. Countries all over the world are trying to find alternative fuel or reduce the consumption, and vigorously developing new energy saving vehicles. In this circumstance HEV (Hybrid Electrical Vehicles) which combine the advantages of internal combustion engines and electric vehicles has sprung up in the world and become the focus on novel vehicle development. However, the tough in-vehicle operating environment and high performance requirements of batteries make the battery technology become the bottleneck of the development of HEV.In order to reach a certain voltage or power level, HEV batteries need to be put in series. But each cell can not be exactly the same in their initial capacity, self-discharge, and charge efficiency, which make the batteries exist imbalance.The imbalance will enlarge after several cycles. Not only do they affect the performence of other cells, but also reduce the cycle life of the battery series. Therefore, during HEV cells working time, the imbalance between cells is a very harmful factor, and equalization of the battery series is highly necessary.The aim of this paper is to solve the imbalance problem of batteries for HEV, and to design a battery management system with a equalization module for HEV batteries,which realizes automatic voltage detection and balancing function. The monitor board uses a multi-cell measuring chip named LTC6802 which gives fast measurement of battery voltage within 13ms. Meanwhile, the overheating of batteries is avoided by means of effective control of the temperature and fan. In the design, a equalization strategy based on state of chargr is proposed, which improves the efficiency of the balancing of the battery pack and gives maximum control of the circuit temperature. Experimental testing has also been done for different modules. The results show that the balancing effect is obvious, and the circuit is stable.
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