Piecewise Small-Signal Modeling and Stability Analysis of DR-MMC HVDC System for Offshore Wind Farms via Floquet and Filippov Theory

The diode rectifier (DR) modular multilevel converter (MMC) high-voltage direct current (HVDC) has generated increasing interest in connecting deep-sea offshore wind farms. To evaluate the system stability, this article introduces the Filippov theory to describe the system behavior during the switching of DR, which is the key to accurately modeling the DR-MMC HVDC system. Given that the obtained small-signal model is piecewise and time-varying, combining it with Floquet theory enables a comprehensive analysis of system stability. Compared to the existing model, the proposed model fully incorporates the switching dynamics and commutation process of DR, offering a precise depiction of the system’s stability range as parameters vary. In contrast, the existing model tends to yield inaccurate stability analysis results. The correctness of stability analysis results is verified by electromagnetic transient tests from RT-LAB.