Active Thermal Control Based on Hybrid Modulation Strategy for MMCs

Modular multilevel converter (MMC) commonly uses modulation strategies such as phase shifted carrier pulse width modulation (PSC-PWM) and nearest level modulation (NLM). Compared with NLM, the output power quality of MMC with PSC-PWM is better. Compared with PSC-PWM, the switching loss and junction temperature of power devices with NLM strategy are lower. Combining the advantages of PSC-PWM and NLM strategies, this paper proposes a hybrid modulation strategy, according to the probability distribution of wind speed in wind farm, the active thermal control of MMC is realized by switching appropriate modulation strategy, which effectively improves the life of power devices, and ensures that the harmonic distortion rate of grid-side current can meet the requirements of wind power grid-connected.