A New Modular Multilevel Converter Circuit Topology with Reduced Number of Power Cells for DC to AC Applications

This paper proposes a new circuit topology of Modular Multilevel Converter (MMC) for grid connected applications. The power cells in each lower arm of conventional MMC are replaced by a passive filter in the proposed topology. The passive filter is an LCL filter and is designed in such a way that it restricts the flow of fundamental current through it. However, it allows the DC and second harmonic component (generated in the upper arm due to power oscillation) to flow through it. As the power cells in the lower arms are removed, the total number of power cells required in the new topology also reduces to half as compared to conventional MMC. Additionally, DC bus voltage requirement is reduced to half to produce the same quality and magnitude of AC voltage waveform as conventional MMC. The theoretical analysis is validated by simulation and a downscaled experimental prototype and the results confirm the proper operation of the proposed converter.