Parallel Operation Modulation Strategy Based on Three-Layer Objective Switching Sequence Design for Coupled Ten-Switch Inverter

Coupled ten-switch inverter is a potential solution for paralleled inverters in medium voltage applications due to the lower cost. However, coupled ten-switch inverter lacks medium vectors, which greatly reduces the vector combinations during parallel operation, the existing methods are no longer applicable. To solve this problem, this paper proposes a modulation strategy without the medium vectors to suppress zero-sequence circulation current (ZSCC), common-mode voltage (CMV), neutral point voltage (NPV) deviation. Based on a three-layer objective switching sequences design, low-CMV vectors are utilized to reduce the CMV, the voltage deviations between two inverters are offset by double vector transpositions to suppress ZSCC, P-type and N-type small vectors are utilized alternately in symmetrical sub-sectors to achieve NPV balance. The effectiveness of the proposed method is verified by simulations.