With the increasing application of power electronic equipment in power systems, the power quality problems of power grids are becoming more and more serious. And the various precision power equipment have higher requirements for power quality. The nine-switch converter has significant advantages in terms of cost and volume, compared with the traditional back-to-back type twelve-switch converter structure. This paper introduces topological structure, pulse-modulation and the mathematical model of the DVR (Dynamic Voltage Regulator) based on nine-switch conversion. On this basis, the method to reduce the DC side voltage of the nine-switch converter is proposed, and the feasibility of the scheme is verified by simulation.