A Coordinated Frequency Regulation Strategy for VSC-HVDC Integrated Offshore Wind Farms

Abstract

The energy stored in the rotor of wind turbines (WTs) and VSC-HVDC capacitors could be utilized if large offshore wind farms (OWFs) through VSC-HVDC transmission are required to provide frequency support to the onshore AC system. This paper proposes a communication-free adaptive coordinated control strategy to allow both OWFs and VSC-HVDC to contribute to the frequency regulation in the onshore AC grid. By means of the proposed approach, the frequency extremes and rate of change of frequency in the onshore grid are reduced, and the offshore system frequency deviation is eliminated, which cannot be achieved by droop control-based strategies in previous studies. The VSC-HVDC is also shown to be able to coordinate with OWFs in the proposed strategy to avoid second frequency drop (SFD) during WT’s rotor speed restoration. The effectiveness of the proposed strategy is verified in case study.