Active participation of variable speed wind turbine in inertial and primary frequency regulations

Abstract

Power systems have increasingly exhibited a need for a potential frequency governor with virtual inertial control (VIC) and primary frequency regulation (PFR) functions in recent years, due to the increased penetration of wind turbines that almost have no frequency response. In this paper, a novel integrated frequency governor applied to a wind turbine is proposed to provide fast active power support and scheduled power allocation for both temporary inertial response and continued PFR. Below rated wind speed, an initial pitch angle is calculated firstly to preset a proper de-loading level for PFR in response to frequency drops, according to the presented relations of CP-λ-β. Under the de-loading operation conditions, the de-loading power tracking curve is replaced by the defined VIC curves, and the inertial response is then obtained by rapidly shifting the VIC curves. Based on analysis of the mechanical characteristics of wind turbines with frequency droop, a primary frequency control strategy facilitated by the regulation of pitch angles is additionally proposed. A preset β/f droop curve is added to the de-loading pitch controller to regulate the mechanical power for scheduled power allocation, and thus satisfying the P/f droop demand of system PFR. Finally, the experiments and simulation results demonstrate that by using the proposed frequency governor a doubly fed induction generator (DFIG) based wind turbine can provide both temporary virtual inertia and continued load sharing to improve the dynamic frequency stability of the power grid with high wind power penetration.