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A modular equalizer using buck/boost converters with snubber capacitors for series-connected supercapacitors

The cell voltage imbalance of series-connected energy storage cells, such as supercapacitors (SCs) and batteries may hurt and even damage the whole energy storage system. Hence, the voltage balancing technology is of great significance to the development of energy storage system. The aim of this paper is to propose a new modular equalizer based on buck/boost converters with snubber capacitors for SCs. Compared with previous methods, the proposed equalizer can balance the voltage quickly and reduce the peak voltage effectively. Detail of the basic operation model was conducted, which indicating the inductance current can be limited without feedback control when operating at DCM. The design for circuit parameters was analyzed based on the model of the equalization time. The simulation results of PSIM and the analysis were in good agreement. Experimental test was performed for 16-series-connected SCs based on the proposed expanded topology. The cell voltage imbalance was gradually eliminated within finite time. In addition, when switches were turned off, the peak voltages were reduced effectively, which verified the basic model. Experimental results were analyzed to prove performance and effectiveness of extensions of equalizing module, which is convenient for application in large-scale energy storage system.