Frequency regulation and droop control of doubly fed induction generators (DFIGs) can quickly respond to frequency changes and reduce the maximum rate of frequency (MROFF) in power systems. However, due to real-time dynamic changes in the MPPT control loop, the ability to improve the lowest frequency point is limited. Therefore, this article first describes an in-depth analysis of the dynamic characteristics of the incremental power of frequency regulation with droop control using an equivalent linear model. The limitations of improving the lowest frequency point under the influence of dynamic changes in the MPPT control loop are revealed. Secondly, to address the impact of these dynamics, an improved decoupling frequency regulation (IDFR) strategy based on power tracking is proposed, aiming to increase the maximum frequency deviation (MFD) and MROCOF. Then, in order to overcome the difficulty of adjusting control coefficients in the IDFR strategy, an adaptive control coefficient tuning fuzzy control method based on frequency deviation and ROCOF was proposed to flexibly adjust control requirements under various working conditions, thereby improving the control stability and performance of the system and effectively solving the problem of control coefficient allocation. Finally, to verify the frequency regulation performance of the proposed IDFR strategy under various operating conditions, simulations were conducted based on different disturbances and wind conditions. The results show that the proposed IDFR strategy significantly improves the system MFD and MROCOF improvement ability under various conditions.

Grid frequency must be regulated in its nominal range to guarantee the stable operation of an electric power grid. Excessive grid frequency excursions result in load shedding, grid frequency instability, or even synchronous generator damage. With the growing wind penetration, there is an increasing issue about the reduction in inertia response. This paper addresses a self-adaptive inertial control strategy for improving the frequency nadir and smoothly regaining the rotor speed to the initial working condition without causing a second frequency drop (SFD). The first objective is achieved by determining the incremental power considering the maximum rate of change of frequency; the secondary goal is realized by smoothly decreasing the power reference based on the decreasing function. Simulation results verify that the proposed control strategy not only boosts the frequency nadir but also guarantees the smooth rotor speed recovery with a negligible SFD.

This paper proposes an innovative inertial response imitation (IRI) and rotor speed recovery (RSR) control scheme of a doubly-fed induction generator (DFIG, Type 3 wind turbine generator) to provide better frequency support response and RSR services for a high wind power penetrated electric power grid. To achieve the first benefit, the coupling relationship between the control coefficient of DFIGs and the frequency deviation was established by using the exponential function so that the control coefficient becomes large with the increasing frequency deviations and sizes of disturbance. After supporting the system frequency, the exponential function was employed to schedule the dynamic control coefficient to alleviate the negative effects of RSR on the instantaneous system frequency. The benefits of the proposed IIR and RSR strategy were investigated in a test system under various scenarios of sizes of disturbance and wind speed conditions. Test results clearly demonstrate that the proposed IIR and RSR strategy is capable of boosting the maximum system frequency excursion and reducing the negative influences on the system frequency during the speed recovery period.

This work develops a grid-forming control framework integrated with supplementary energy storage, so that permanent-magnet direct-drive wind turbines can deliver primary frequency regulation and inertial support services. Current stability research commonly concentrates on turbine-grid interactions, yet overlooks coupling dynamics at the DC-link, which motivates this study to establish a quantitative stability evaluation approach for grid-forming wind-storage systems with DC-side coupling taken into consideration. Small-signal impedance representations are firstly constructed for the machine-side converter (MSC), grid-side converter (GSC), and energy-storage converter with respect to the DC-link. On this basis, quantitative investigation is carried out to clarify how grid stiffness, inertia coefficient, droop gain, as well as charging/discharging operating modes of energy storage shape the DC-side stability margin of the hybrid system. To boost DC-link electrical damping, a supplementary stabilizing control scheme is embedded within the control loops of the energy-storage converter. Simulation outcomes reveal that the inertial support loop may inject negative damping and impair DC-link stability. Besides, discharging operation yields better stability performance for the wind-storage configuration relative to the charging condition. The devised stabilizing controller is capable of strengthening DC-side stability, enabling simultaneous inertial response and primary frequency support. Validations based on the PSCAD/EMTDC environment confirm the accuracy of theoretical deductions and the practical performance of the presented control solution.