Two-Switch Voltage Equalizer Using a Series-Resonant Voltage Multiplier Operating in Frequency-Multiplied Discontinuous Conduction Mode for Series-Connected Supercapacitors

Cell voltage equalizers are necessary to ensure years of operation and maximize the chargeable/dischargeable energy of seriesconnected supercapacitors (SCs). A two-switch voltage equalizer using a series-resonant voltage multiplier operating in frequency-multiplied discontinuous conduction mode (DCM) is proposed for series-connected SCs in this paper. The frequency-multiplied mode virtually increases the operation frequency and hence mitigates the negative impact of the impedance mismatch of capacitors on equalization performance, allowing multi-layer ceramic capacitors (MLCCs) to be used instead of bulky and costly tantalum capacitors, the conventional approach when using voltage multipliers in equalizers. Furthermore, the DCM operation inherently provides the constant current characteristic, realizing the excessive current protection that is desirable for SCs, which experience 0 V and equivalently become an equivalent short-circuit load. Experimental equalization tests were performed for eight SCs connected in series under two frequency conditions to verify the improved equalization performance at the increased virtual operation frequencies. The standard deviation of cell voltages under the higher-frequency condition was lower than that under the lower-frequency condition, demonstrating superior equalization performance at higher frequencies. key words: cell voltage equalizer, discontinuous conduction mode (DCM), frequency multiplier, series-resonant voltage multiplier, supercapacitors (SCs)