To build the new power system with the main body of new energy, the offshore wind farm (OWF) is an important part and has been rapidly developed in coastal cities. However, the large-scale OWFs also reduce the inertia of power systems, which significantly decreases the anti-disturbance capability of system frequency Therefore, a synthetic inertia control strategy for OWF based on dual phase-locked loops (PLL) was proposed. First, the influence mechanism of PLL on virtual inertia of wind turbine was theoretically analyzed for variable parameter PLL. And the variation rule of wind turbine inertia support capacity and system frequency response characteristics with parameter changing PLL was explored. Then, the double PLL based OWF frequency regulation strategy was proposed through analyzing the negative effect of primary frequency regulation characteristics caused by the variable parameter of PLL. Finally, the effectiveness of the proposed frequency regulation strategy was verified though simulations. The results show that the proposed method has significant advantages in frequency response speed and frequency measurement noise suppression.
