A virtual inertia control method for variable-speed wind turbines is proposed based on the switching of power point tracking curves. In this method

when power grids are in normal states

the wind turbines operate with the nearly maximum power point tracking(MPPT)curve

and the kinetic energy is stored; when the frequency of power grids drops

the wind turbines switch to another nearly MPPT curve to operate

and kinetic energy is released to support grid frequency. The adoption of the suboptimal curve switching mechanism can significantly reduce the interaction between the df/dt feed-forward control loop and the original control loops

hence improving the dynamic response performance of the virtual inertia control. By the proper selection of the suboptimal power point tracking(SOPPT)curves

the reduction of wind power conversion efficiency caused by inertia control can be reduced. In the simulation cases

the captured wind power is always ensured no less than 98% times of the MPPT power during the inertia control of wind turbines.