An Isolated Hybrid Sigma Bi-directional BESS Interface with Extra-Wide Voltage Gain

A combination of resonant topology with partial power processing concept is used to achieve high efficiency and wide voltage gain. The proposed topology is called a hybrid sigma converter. The transformer turns ratio must be designed to achieve optimal power split and feasible regulator voltage ratio across all operating points. The built prototype is able to provide voltage gain from 5.08 to 11.97. Currently, the peak efficiency is 95%, however, with lower Rds on the low-voltage side, it can be improved to 98%. A cascaded PI with hysteresis comparator is implemented to control the bipolar regulator stage. A smooth transition for a wide voltage range is achieved in simulation.