Research On The Dynamically SOC Estimating Strategy And The Balancing Technology Of LiFePO₄ Batteries

The development of hybrid vehicles is an important measure to promote energy conservation and emission reduction and to implement the green automobile industry. As the key components of hybrid electric vehicle, power batteries is a significant impact of the HEV's development in terms of the dynamical performance, security and economy.Therefore, in-depth research on battery management and balancing techniques has the great significance and engineering application value for improving the performance of hybrid vehicles, guaranteeing the safe operation of the battery, prolonging battery lifetime.Firstly, This article analyses a number of important factors affecting the SOC(State Of Charge) of the batteries based on the internal structure and reaction mechanism of LiFePO4 batteries; Secondly, deeply analyses the power batteries'demands of the hybrid vehicle, as well as the lithium-ion battery indicators in the national 863 project; Thirdly, this article also describes some of the existing battery models, brings forward a method of dynamically estimating the SOC.The voltage of one battery cell is limited, so hybrid electric vehicle battery typically takes a number of single cells in series. Due to factors such as the existence of manufacturing error, the batteries must have differences of internal resistance, voltage, capacity, and other parameters between each other. So the estimation of SOC of single cell is not the same as the SOC estimation of the entire pile. Because of the differences between ventilation and radiator cooling, the differences in energy conversion, and the over-charge or over-discharge instances, the battery will gets aggravated. So the SOC estimation of static state and the SOC estimation of dynamic state are also not the same. In order to balance the battery packs and solve the impact of complicated road conditions on the accurate estimation of SOC, the system needs to add dynamic estimation strategy and algorithm to optimize the equilibrium subsystem. This article focused on the imbalance of LiFePO4 batteries under dynamic load, and brings forward the dynamic SOC estimating method.The results of the experiments prove that this method can effectively make batteries avoid over-charging or over-discharging. This article specifically designed "low charge and high discharge " balancing subsystem, and introduced the " electrical balancing method" balancing strategy, strategy combined with single chip, make the appropriate balance of power compensation. Test results showed that, to a large extent, the system reduces the inconsistency of battery performance.For the sake of satisfying HEV power batteries relevant tests requirements, the high power batteries test bench is used. The test bench can do charge and discharge power battery packs, according to the vehicle requirement. During the test, Lab VIEW can acquire and save related parameters for BMS control strategy in real time. At the same time, some test devices, such as Digatron battery test system, multi-channels battery pack face to face charge test bench, battery dynamic performance test system and FLULK power analyzer, etc. are used to do battery pack charge and discharge tests, efficiency test, simulate vehicle working condition test and endure test, and so on.Results show that the dynamic SOC estimate method of this research programme and the balancing technicnology are reliable, and play very good on accurate estimation of SOC and the improvement in battery performances. The capability of the batteries increases 10 percents as a result.