Experiment on nearest level modulation algorithm for FPGA based Modular Multilevel Converters

Modular Multilevel Converter (MMC) has been applied to medium and high - voltage power systems recently because it has many advantages over other multilevel converters. This paper will present the algorithms of Nearest Level Modulation (NLM) and capacitor voltage balancing to greatly reduce the switching frequency as well as producing an output voltage at the AC side with very low harmonic distortion. The experimental system for the MMC converter requires a large amount of I/O signals ports. However, Digital Signal Processor (DSP) only provides up to 24 I/O signals ports while the experimental system of the MMC converter needs more than that. In this paper, the experimental system used FPGA to embed the proposed methods and applied to an MMC with 12 Sub-Modules (SM) to generate a 13-level AC voltage waveform. In this case, FPGA is the most suitable choice to develop the control circuit for the experimental system of MMC. The effectiveness of the proposed algorithm was verified by simulations and tested using a laboratory – scale prototype.