Control of modular multilevel transformerless cascaded bidirectional converters

This paper presents transformerless cascaded bidirectional converters with a cascaded five level rectifier stage, a DC/DC converter stage composed of two Dual Active Bridge (DAB) and a cascaded five level inverter stage. However, the cascaded converters lead a complex control algorithm and suffer from voltage imbalance between the multiple floating dc capacitors. This paper discusses and compares different control methods to resolve the voltage unbalance on the dc links of different H-bridges. Based on the minimum point of backflow power, the paper proposes a novel control method to the converter. Results of experiments are presented to verify the performance under unbalance loads.