An improved circuit topology of modular multilevel converter (MMC) for DC to AC applications

This paper proposes a new circuit topology of MMC for DC to AC applications. The main advantage of the proposed topology is the elimination of lower arms of conventional MMC. Additionally, the DC bus voltage magnitude is half compared to conventional MMC. This is achieved by replacing the lower arms of conventional MMC topology with LC filter. The LC filter is designed to be a second order band stop filter which prevents the fundamental current to flow while allowing the DC and other harmonic currents to circulate. Operating principle and design of filter are included in the paper. The proposed circuit topology can be used in any DC to AC applications or grid connected applications e.g. STATCOM (Static Synchronous Compensator) or UPQC (Unified Power Quality Compensator).