In modern power systems, the increasing penetration of renewable energy resources has reduced the overall system inertia. However, the intermittent nature of wind power generation reduces frequency stability, which is a crucial issue. Consequently, modern power systems require that renewable energy sources, such as offshore wind farms, support the frequency regulation. High voltage direct current (HVDC) systems based on voltage source converters (VSCs) are currently being used to connect wind farms with the main grid. By adjusting the DC-link voltage of the VSC-HVDC, a capacitor can absorb or release energy to provide frequency support. In addition, the VSC-HVDC system can coordinate wind farms to support frequency regulation and thereby achieve better performance. Thus, this paper reviews and compares various frequency-control strategies for a VSC-HVDC-connected wind farm. This work implements in PSCAD/EMTDC a simulation of typical frequency-control techniques to verify their effectiveness and robustness. Furthermore, this paper shows the advantages and drawbacks of each frequency regulation method. Other auxiliary services for supporting frequency regulation, such as by energy storage systems, are also discussed. Finally, this paper provides complete recommendations for frequency regulation techniques for VSC-HVDC-integrated wind farms.

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