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In the traditional energy storage systems consisting of series connected energy storage cells such as electric double-layer capacitors (EDLCs), not only a bidirectional PWM converter but also a cell voltage equalizer is required. The system is prone to complexity as two converters (i.e., the bidirectional converter and cell voltage equalizer) are separately necessary. This paper proposes the transformer-less bidirectional PWM converter integrating the voltage multiplier-based cell voltage equalizer. An inductor in a conventional bidirectional PWM converter is replaced with series-connected inductors in the proposed converter in order to generate square wave voltage with an arbitrary amplitude, by which the voltage multiplier is driven. The charge-discharge cycling test for nice EDLCs connected in series was performed using the proposed integrated converter from a voltage-imbalanced condition. The voltage imbalance was gradually eliminated while charge-discharge cycling, demonstrating the integrated functions. TRANSFORMER-LESS BIDIRECTIONAL PWM CONVERTER INTEGRATING VOLTAGE MULTIPLIER-BASED CELL VOLTAGE EQUALIZER FOR SERIES-CONNECTED ELECTRIC DOUBLE-LAYER CAPACITORS