Cell voltage equalizer using series resonant inverter and voltage multiplier for series-connected supercapacitors

A cell voltage equalizer using a series-resonant inverter and voltage multiplier is proposed. Unlike conventional equalizers that require multiple switches and/or magnetic components, the proposed equalizer can be configured with two switches and a single magnetic component. This means the circuitry can be significantly simplified and scaled down compared to conventional equalizers. Furthermore, because the series-resonant inverter inherently outputs a constant current when operated in discontinuous conduction mode (DCM), currents in the equalizer can be limited as desired without feedback control; further simplifying the circuitry by eliminating the feedback control loop. Fundamental analyses for the series-resonant inverter and voltage multiplier are separately performed to verify the constant current characteristic of the series-resonant inverter and the equalization mechanism by the voltage multiplier. An experimental equalization test was performed for eight supercapacitors (SCs) connected in series. The voltage imbalance was gradually eliminated as the SC energies were redistributed by the equalizer, demonstrating the equalization performance.