Grid Code Compatibility of VSC-HVDC Connected Offshore Wind Turbines Employing Power Synchronization Control

This paper presents an alternative control scheme for offshore wind turbines (WTs) connected to the mainland grid through high voltage dc (HVDC) links based on voltage source converters (VSCs). The proposed WT controller inherently provides rapid droop-type frequency response, without the need to implement an additional WT frequency controller. A coordinated control approach is proposed between the WT and HVDC controllers in order to achieve fault ride-through (FRT) and frequency response capabilities, relying solely on offshore frequency modulation. To demonstrate the FRT capability of the VSC-HVDC link, a detailed EMT-type model is first developed in Matlab/Simulink, where onshore grid faults are tested. Then, the offshore wind farm is connected to a study case system in order to assess the contribution of the VSC-HVDC link to frequency regulation, by exploiting the proposed WT controller along with the communication capability between the two HVDC VSCs.