Research on DC voltage balancing control method of star connection cascaded h bridge static var generator

The in-depth study of the DC voltage balancing of the star connection cascaded H bridge multilevel static var generator (SVG) has been made in this paper. And the control system with three layers of the DC voltage balance has been established. The first layer is the total DC side voltage control, which is maintained to be constant through generating the fundamental positive sequence active current. The second layer is the balancing control between three phases. Through the injection of the zero sequence voltage into the command voltage, we can make the redistribution of the three-phase power, so as to realize the DC voltage balance between three phases. In this method, through feeding forward the power generated by the grid voltage and the output current, the rapid dynamic regulation can be achieved. The third layer is the balancing control among modules in each phase. Through fine tuning the command voltage of each module in each phase along the direction of the current, we can make the redistribution of the power absorbed by each module, so as to ensure that the DC side voltage of each module in each phase is equal to the given value. Experimental results verify the correctness and reliability of the proposed control method in the end.