Efficient Equalization Topology And Efficiency Analysis Of Energy Storage Power Pack Series

Power battery and ultra capacitor and other voltage source are widely used inelectric vehicles, new energy power generation, communication power supply andother fields. It needs many cells to constitute a power pack to meet the power supplyvoltage. But the parameter inconsistency between cells causes the weak cellovercharge or overdischarge, and reduces the capacity of the power pack, shortens thelife of the pack, also it may cause security problems. Therefore, it needs to equalizethe voltage of the power pack, but the performance of the entire system is directlyinfluenced by equalization structure. This paper analyzes the existing equalizationtechniques. Considering the equalization speed, efficiency and other requirements, adouble-layer equalization system is designed.Commonly used equalization structures are analyzed in this paper with graphtheory, theory of probability. The effect of structure to equalization efficiency andenergy path is emphasized. Based on the results, the flying capacitor and single-tubemulti-winding flyback structure are better in energy transfer path, balancing efficiency;Graph theory applied in this field provides new way for studying in more complexstructure, developing equalized control strategy, building new circuit topology;Proposed that equalization system multilayered can improve system performance.Double-layer equalization system of nine cell power series pack is builded, thelower layer adpots multi-winding flyback converter structure, and the upper adpotsflying capacitor structure. The lower layer multi-winding transformers and snubbercircuit, main circuit of upper equalizer are designed on the analysis of two layerequalizers principles and problems. The effects caused by circuit parameters on theefficiency of the system is analyzed which will help to improve system efficiency andsystem architecture optimization.The controller of this two-layer equalization system is designed. For the defectsof upper structure, the low voltage drop bidirectional power switches of twoMOSFETS, wide pulse transformer drive circuit is developed that ensure rapid andefficient equalization of upper layer. Develop control strategies, design equalizersoftware to ensure that the upper and lower equalization system reliable and stableoperation.Also this paper builds double-layer system simulation and experimental platformsystem with nine cells, and then tests the efficiency of each layer. The result showsthat the double-layer structure has faster speed and higher efficiency.