DC Side Harmonic Resonance Analysis of MMC-HVDC Considering Wind Farm Integration

In a modular multilevel converter (MMC) based wind farm integration system, the wind farm may influence the harmonic resonance characteristics of DC system through the connected MMC. An effective way to assess the harmonic resonances in DC system is the impedance analysis method, in which the key is to develop the DC side impedance model. This paper develops the dc impedance of the wind farm connected MMC by harmonic transfer function (HTF) method that considers both the dynamics of the MMC and wind farm. As a result, the proposed DC impedance model can effectively reveal the impact of the wind farm on the small-signal characteristics of the DC system. Compared to the existing model, the proposed model can improve the accuracy of DC system resonance analysis with consideration of connected wind farm. Therefore, the proposed model can be further used to assist the stability design of wind farm connected MMC-HVDC systems. The time-domain simulations in PSCAD/EMTDC validate the proposed impedance models and stability analyses.