Sliding mode capacitor voltage control in extended commutation cell based inverter

An extended commutation cell (ECC) is a four-port four-switch power processing cell that allows for bidirectional energy transport in two orthogonal directions throughout the structure. By cascading multiple cells a high-quality output voltage waveform can be constructed with a high number of levels. The voltage across each cell capacitor can be adjusted independently of the load, resulting in a high flexibility in output levels. This paper derives a robust sliding mode control algorithm for capacitor voltage control in ECC based converters. It includes a cell current estimator, being intended for fast regulation of the internal states of each cell. The proposed method is analyzed, simulated and experimentally verified on a 4.4 kW eight-level inverter prototype.