Adaptive Inertial Control for Wind Turbine Generators in Fast Frequency Response Based on the Power Reduction Period Assessment

Fast frequency response of wind turbine generators (WTGs) is achieved by injecting incremental power to the grid followed by power reductions to avoid over-deceleration and ensure secure rotor speed recovery. Second frequency deeps (SFDs) are the results of such power reductions that are challenging during abrupt frequency transients that may lead to under-frequency load shedding, or cascading events leading to blackouts. To address this issue, this paper presents an adaptive inertial control (AIC) scheme for WTGs designed to maximize the improvement in frequency nadir without causing SFD. The proposed method is developed through an assessment of power reduction period of WTGs during fast frequency response. This analysis investigates the impacts on the system frequency of a) injecting different shares of disturbance size (SoDSs) by WTGs and b) latency/delay in power injection. Derived from this analysis, the AIC is proposed to inject the maximum possible SoDS during the over-production period and successfully stabilize and recover the rotor speed during the assigned optimal power reduction period with SFDs disabled. This is achieved by adaptively adjusting the AIC in the reduction period based on the SoDS injected by WTGs during the over-production stage. Also, the AIC is modified to adapt against wind speed deviations. To evaluate the performance of the AIC, a comprehensive verification is carried out by comparing AIC with thirteen existing inertial control schemes and maximum power point tracking control in various cases using wind-integrated IEEE 39-bus system in Digsilent PowerFactory and real-time experimental tests. The results confirm the effectiveness of AIC in terms of achieving maximum improvement in frequency nadir without generating SFD.