A hybrid Modulation method for improved modular multilevel converter applied for power quality compensation in medium voltage

In this paper, an improved MMC structure is presented for power quality compensation in medium voltage, which has a special SubModule working in High Switching Frequency (SM-HSF) and N SubModules (SMs) in each arm. Then, a hybrid Modulation method in which Pulse Width Modulation (PWM) for SM-HSF is combined with Nearest Level Modulation (NLM) for SMs is introduced for this improved MMC structure. It can output the same voltage waveform with less harmonics than modulated by NLM, lower switching frequency and losses level than CPS-PWM. In order to confirm the modulation method, a series of modules are established in PSCAD/EMTDC.