Research on DC capacitor voltage self-balancing space vector modulation strategy of five-level NPC converter

DC capacitor voltage balance is one of the key issues in the control of five-level NPC (neutral point clamped) converter. In this paper, it analyses the influence of space vectors to the DC voltage balance in five-level NPC converter SVM (space vector modulation) strategy and present a novel DC capacitor voltage self-balancing SVM strategy. The novel strategy divides the whole five-level space vector diagram into low modulation region (m_SV≤0.5) and high modulation region (m_SV>0.5). In low modulation region, DC capacitor voltage balance is achieved by combining objective function method with reference voltage decomposition method. In high modulation area, DC capacitor voltage balance is realized by applying an optimal balancing vector selection (OBVS) method. The characteristics of the novel strategy are smaller amount of calculation, much simpler realization and better control effect. Simulation and experimental results verify the correctness of the proposed method.