An alternative frequency-droop scheme for wind turbines that provide primary frequency regulation via rotor speed control

Abstract

This paper proposes a frequency-droop control scheme for wind turbines using rotor speed control. The control scheme is proposed as a better alternative to conventional frequency-droop control techniques. When conventional frequency-droop control is used, the frequency response produced by the wind turbine is dependent on the method of power tracking employed. When power tracking is achieved using torque control, the wind turbine’s frequency response is limited to short duration responses, even when operating reserve is available via de-loaded power tracking. This means that reserves cannot be fully utilised. When power tracking is achieved using power signal feedback, conventional frequency-droop methods under-deliver on the expected frequency-droop response due to rotor deceleration during frequency response. The proposed control scheme is unaffected by rotor deceleration and the method of power tracking employed as primary frequency regulation is achieved by varying the wind turbine’s power tracking curve, rather than adding droop control signals to the wind turbine’s power tracking reference. The effectiveness of the control scheme is validated through simulations using DIgSILENT PowerFactory. The results show that the control scheme produces the same frequency regulating response in wind turbines that achieve power tracking using torque control as those that use power signal feedback. This is an improvement on conventional frequency-droop control techniques and will improve the consistency and predictability of frequency regulating services procured from wind farms.