Experiment on Nearest Level Modulation algorithm for FPGA based Modular Multilevel Converters

Modular Multilevel Converters (MMC) have many advantages in comparison with conventional multilevel converters in application to high voltage system. However, the control system of MMC requires a large amount of I/O signal ports which cannot be generated by a single digital signal processor (DSP) with maximum I/Oport of 24. This paper fucuses on the experimental results of a MMC that uses a Field Programmable Gate Array (FPGA) in which embedge the Nearest Level Modulation (NLM) method and capacitor voltage balancing algorithm. The MMC consists of 12 Sub-Modules (SM) in each phase to generate a 13-level ac output voltage. Applying the NLM method and capacitor voltage balancing algorithm have significantly reduced the switching frequency and produced an ac output voltage with very low harmonic distortion. The experimental results have verified by a laboratory-scale prototype and compared with the simulation results.