Voltage and Frequency Analysis of Offshore Wind Farms Following MMC DC-side Fault

DC short-circuit faults represent a primary challenge to the development and deployment of offshore wind energy using modular multilevel converter (MMC) based high voltage direct current technology. The core difficulty in using alternating current circuit breaker (ACCB) to address such faults lies in maintaining the AC-side voltage and frequency stability after offshore MMC blocking. This paper establishes mathematical expressions for the offshore AC-side frequency and voltage before and after ACCB activation, identifying the related system parameters. The findings are validated by MATLAB/Simulink simulations, showing that the proposed frequency expressions have a prediction error of only 3.5% over 200 ms. Based on the theoretical analysis, the paper demonstrates that the stability of the voltage and frequency can be effectively achieved by tuning the output voltage limiter and current references of the wind turbine’s grids-side converter without altering its operating mode.