A frequency response strategy for variable speed wind turbine based on a dynamic inertial response and tip-speed ratio control

Participation of the wind turbine generators (WTGs) in the frequency regulation service is an appealing issue in order to consider the safe increasing of the wind power generation. The droop and virtual inertia control are the most popular approaches that facilitate the WTGs to provide frequency regulation. However, the intermittent nature of the wind complicates the implementation of these methods and has impacts on the wind turbine stability and may cause violation of the allowed power reserve and minimum turbine rotor speed. Therefore, in this paper, a control approach based on the dynamic de-loading technique is proposed, where the wind turbine operating curve is dynamically adjusted in the response of the frequency deviation throughout controlling the turbine tip-speed ratio which helps the turbine provide steady-state power sharing within the reserved power as well as the transient response within its stability criteria. In addition, the inertial response based on a dynamic gain is suggested. The inertial weighting gain has been formulated where it is continuously regulated in the response of rotor speed and reflects the amount of available kinetic energy in the rotating mass. The effectiveness of the proposed control approaches is verified throughout the comparisons of the results with the fixed inertial gain control and the droop control. The simulation results confirm that the combined control of the proposed tip-speed ratio and dynamic inertia control improve the overall system dynamic behavior in terms of frequency response and turbine stability.