The traditional proportion-differential (PD) virtual inertia control strategy enables directly-driven wind turbines to provide frequency support for the main power system. However

the frequency regulation is not effective since the control strategy introduced to the grid-connected wind farms using fixed control parameters and algorithms. This paper provides a novel method calculating the parameters in the PD virtual inertia control and analyzes the influence of rotor kinetic energy and converter capacity in different wind speed intervals on the frequency regulation ability of directly-driven wind turbines. A coordinated virtual inertia control strategy considering different frequency regulation abilities of wind turbines is proposed. The rotor kinetic energy evaluation factor and converter capacity limit factor are introduced to reflect power coordination. Simulation results demonstrate that this strategy maximizes the frequency regulation abilities of directly-driven wind turbines and avoids the secondary drop phenomenon of system frequency

while further improves the main system frequency regulation results. This work is supported by National Basic Research Program of China (973 Program) (No. 2012CB215103) and National Natural Science Foundation of China (No. 51077130

No. 51377167).