Single-Switch Multioutput Charger Using Voltage Multiplier for Series-Connected Lithium-Ion Battery/Supercapacitor Equalization

Voltage equalization is essential for series-connected energy storage cells, such as lithium-ion cells and supercapacitors (SCs), because it ensures years of service life and maximizes the available energies of cells. Conventional equalizers and multioutput chargers require many switches and/or a multiwinding transformer, which are not desirable in terms of circuit simplicity and extendibility. In this paper, single-switch multioutput chargers based on a combination of an input cell (which generates a square voltage wave) and a voltage multiplier (which produces multiple uniform output voltages) are proposed. A fundamental operation analysis is made, and a dc equivalent circuit is derived to describe their charging and equalization behaviors. Experimental charge tests were performed separately for series-connected SC modules and lithium-ion batteries from voltage-unbalanced conditions. The least charged module/battery was charged preferentially; as a result, all of the modules/batteries were charged to a desired uniform voltage level while eliminating the voltage imbalance.