Analysis of back-to-back MMC for medium voltage applications under faulted condition

摘要

This paper analyzes a 10MW medium voltage Back-to-Back (BTB) Modular Multilevel Converter (MMC) without a DC-Link capacitor with half-bridge submodules. It focusses on the system behavior under single-line-to-ground (SLG) fault when there is no capacitor on the DC-Link. The fault current is computed numerically and compared with the simulated results. The converter control behaviour with regards to the injection of the positive sequence currents in the presence of unbalanced terminal voltages has been investigated. Finally, the converter protection using cell level chopper control strategy is presented to prevent DC overvoltages in the sub-modules during faults.