Inertia Emulation of PMSG-Coupled Wind Turbines with Rotor Speed Recovery Support from DC-link Capacitors

The increasing amount of variable speed wind turbines (VSWTs) is witnessed by modern power systems. However, this high-penetration level of wind energies leads to the reduction of power system inertia. To solve the lack of inertia issue, releasing the kinetic energy stored in the rotating masses of Permanent Magnet Synchronous Generator (PMSG)-coupled wind turbines is promising, through which inertia emulation and frequency support can be achieved. However, during the speed recovery period, wind turbines must absorb energy from the grid, which will lead to a secondary frequency drop. To avoid this unfavorable event, this paper proposes to use DC-link capacitors for compensation of the power mismatch and mitigation of the secondary frequency drop during the rotor speed recovery period. By regulating the output power of DC-link capacitors to equal the power absorbed by wind turbines, the grid frequency remains undisturbed. Finally, the feasibility of the proposed method is verified by simulation and experimental results.