Research on DC Voltage Balancing Strategy of Single-Phase Cascaded Solid State Transformer

The disadvantages in power system with traditional industrial frequency transformer can be resolved by SST (solid state transformer). Cascaded SST can be transformerless connected to the high voltage grid. However, the output performance and reliability of cascaded grid-connected inverter are seriously influenced by DC voltage balancing problem which exists in cascaded configuration. Firstly, circuit topology, operating principle and mathematical model of single-phase cascaded SST are analyzed. Then, active power adjusting ability of DC voltage balancing methods are compared. Finally, suitable DC voltage balancing method is confirmed. This method can balance the DC voltages even under complex condition. Experimental results verify the feasibility and validity of this method.