Analysis of the performance of MMC under fault conditions in HVDC-based off-shore wind farms

Abstract

This paper analyzes the behavior of a modular multilevel converter-high-voltage direct-current (MMC HVDC)-connected offshore wind power plant (WPP) during dc faults. For that purpose, detailed models of the dc cable, MMC stations, and transformers have been used in order to obtain reliable results. The influence of the WPP control method in the short-circuit behavior of the HVDC link has also been studied. Results show that the dynamics of the WPP contribution to pole-to-ground faults are slightly slower than those of the wind turbines current control loops. Therefore, the wind turbine front-end converters can be used to reduce the peak and average value of the fault current in such a system. Moreover, it has been found that ferroresonant oscillations can appear in the offshore ac grid when the WPP delivers constant power during faults.