Direct Cell-to-Cell Voltage Equalizer Using Capacitively-Isolated Parallel-Resonant Converter for Series-Connected Energy Storage Cells

摘要

Direct cell-to-cell voltage equalizers have been proposed for series-connected energy storage cells, such as lithium-ion batteries and electric double-layer capacitors (EDLCs). Conventional direct cell-to-cell voltage equalizers, however, require a transformer for isolation, resulting in increased circuit volume. In this paper, a capacitively-isolated parallel-resonant converter is proposed to miniaturize the circuit volume by employing capacitive isolation, instead of a bulky transformer. No feedback control is necessary for the proposed converter to limit its currents under desired levels, and safe operation is feasible even when some cell voltage is 0 V because of the inherent constant current characteristic of the parallel resonant converter at a fixed switching frequency. A 1.0 W prototype and cell selection switch module for twelve cells connected in series were built, and an equalization test for EDLCs was performed from voltage imbalanced condition. The voltage imbalance was eliminated by the proposed equalizer, demonstrating the efficacy of the equalization performance.