Modified modulation strategy of MMC for wind farm integration

Voltage source converter‐high‐voltage DC (VSC‐HVDC) technology is considered an advantageous solution to be applied to large‐scale wind power integration. VSC‐HVDC are mostly based on the modular multilevel converter (MMC), which generally adopt nearest level modulation (NLM) strategy. If the MMC adopts traditional NLM strategy, then when a disturbance or fault occurs in the system, so that the dc voltage fluctuates, the output ac voltage of MMC will have poor stability, and that is unable to meet the demand for wind farm integration. This study analyses the reason of above defects of traditional NLM strategy, and proposes an improved modulation strategy. The improved strategy considers the actual value of the capacitor voltage, so that the output ac voltage of MMC has good stability. By building an electromagnetic transient model in PSCAD/EMTDC and doing simulation analysis, this study verifies that the improved modulation strategy can effectively enhance the ac voltage stability of converter station which has wind farm integrated, so as to enhance the operational stability and security both of the VSC‐HVDC system and wind farm.