A Delta-Structured Switched-Capacitor Equalizer for Series-Connected Battery Strings

The classical switched-capacitor (SC) equalizer is widely used in battery management systems because of the accurate balancing and ease of implementation. However, it only achieves the adjacent cell-to-cell equalization, and its balancing speed and efficiency become extremely low for multicell series-connected battery strings. Therefore, a delta-structured switched-capacitor equalizer is introduced to achieve a high-speed and high-efficiency any-cells-to-any-cells (AC2AC) equalization at arbitrary imbalanced status for any number of cells. The slow switching limit and fast switching limit impedances of the proposed equalizer are developed to provide a theoretical guidance for the optimized design of the SC equalizers. A prototype for four battery cells was built, and a comparison with existing equalizers was presented. Experimental and comparative results show that the proposed solution exhibits an automatic AC2AC balancing with high reliability and strong robustness. The measured balancing efficiency is up to 94.5%.