Modulation Method for Nine-Switch Converter Based on Equivalent Mechanism Between Nine-Switch Converter and Dual Six-Switch Converters

In this article, the equivalent mechanism between nine-switch converter (NSC) and the two six-switch converters (SSCs) is explained in detail. In order to achieve the decoupling of the upper and lower ac terminals, the concept of virtual leg is proposed and the decoupling model of NSC is established based on virtual legs. In this model, the NSC is equivalent to dual constrained SSCs. Continually, the space vector modulation method of NSC is proposed based on dual constrained SSCs modulation for both common frequency and different frequency modes. In the proposed modulation method, the concept of space vector distance function (SVDF) is proposed. SVDF represents the actual switching times between any two actual working states of NSC. The closer distance between the two actual states is, the smaller the actual switching loss will be. Using the modulation method, the NSC can realize the independent control of two sets of three-phase ac voltage and achieve the same control performance as the dual SSCs. The validity of the proposed converter is verified through simulations and experiments.