Research on DC voltage control method of delta connection cascaded H bridge SVG

The in-depth study of the DC voltage balancing for the delta connection cascaded H bridge SVG has been carried out in this paper. A three layer DC voltage balancing control system is proposed. The first layer is the total DC side voltage control. Through generating fundamental positive sequence active current, the total DC side voltage of all three-phase H bridge modules is maintained constant. The second layer is the balancing control between three phases. Through injecting zero sequence voltage into the command voltage to produce zero sequence current, the three-phase power can be redistributed, thus the DC voltage balancing between three phases is achieved. The third layer is the balancing control between each module in each phase. Through fine tuning of the command voltage of each module in each phase along the direction of the current, the absorbed power of each module can be redistributed, thus the DC side voltage of each module in each phase can be kept as the reference value. Experimental results verify the correctness and reliability of the proposed control method in the end.