Research On The Key Issues About Active Equalization System Of LiFeO₄ Power Battery Pack

With the energy crisis and environmental pollution problems become seriously, people pay more attention to the development of electric vehicles. The Li-ion battery has become the preferred energy storage elements for its non-memory, high operating voltage and energy density, low self-discharge rate, long life and other advantages, in terms of electric vehicles and communication systems it has been widely used. However, due to its single cell’s inconsistency, the battery pack becomes over charge or over discharge, therefore the life of the entire battery pack decreases. So it is necessary to adopt appropriate methods to achieve a balanced cell balancing. This paper designed a complete battery equalization system based on the mechanism of cell inconsistencies, and made simulation and experiment. The specific contents are as follows:1.Firstly, this paper introduces the causes of battery consistency problem and its effects, and points out two solutions to solve the problem. Considering the breadth of applications and professional relevance, ultimately this paper focused on the balancing system.2.In the study of battery equalization system, balanced topology is the most basic and most important problems. Comparing the existing problems of equalizer circuit, this paper chooses the DC-DC converter as the balanced topology. Through the module design, the equalizer is more suitable for application in electric vehicles.3.After determining the composite structure of DC-DC converter as balanced topology, this paper designed two control strategies: frequency table look-up control strategy with voltage differences and control strategy based on dynamic balanced point. Because any cell will only release or receive charges, this balancing method of tracing the dynamic balanced point will reduce the energy circulating from one cell to the other cell. Thus, this control strategy can reduce switching losses and accelerate the process of balancing. But the two strategies is based on the battery voltage, and the essence of the battery balancing is SOC. Therefore, this paper made the attempt of SOC.4. Firstly, this paper found the advantages through comparing the look-up table control strategy and dynamic balanced point control strategy by simulation. Then doing the simulation in charge state, discharge state and static state based on dynamic balanced point. Finally, we carried out the experiment in room temperature, and get the good performance.