Transformerless Bidirectional PWM Converter Integrating Voltage Multiplier-Based Cell Voltage Equalizer for Series-Connected Electric Double-Layer Capacitors

In the traditional energy storage systems consisting of series-connected energy storage cells such as electric double-layer capacitors (EDLCs), not only a bidirectional pulsewidth modulation (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 transformerless 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 nine EDLCs connected in series was performed using the proposed integrated converter from a voltage-imbalanced condition. The voltage imbalance was gradually eliminated during charge-discharge cycling, demonstrating the integrated functions.