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Summary This paper proposes a nonlinear controller based on state feedback linearization (SFL) method to mitigate sub‐synchronous control interaction (SSCI) in series‐compensated doubly fed induction generator (DFIG)‐based wind power plants (WPPs). To make full use of the converter control of DFIG, the SFL controller is developed for both grid side converter (GSC) and rotor side converter (RSC) through four necessary steps, ie, assessment of the feedback linearizability, coordinate transformation, feedback linearization, and derivation of control laws. The stability of the internal dynamics, which is not transformed into linear autonomous subsystems in the design process of the RSC controller, is ensured by the application of zero‐dynamic theory. A 100‐MW DFIG‐based WPP adapted from the IEEE first benchmark model is utilized to evaluate the effectiveness of the SFL damping controller at different wind speeds and compensation levels, and the capability of the proposed controller in mitigating SSCI is compared with a well‐tuned proportional‐integral controller and a conventional SSCI damping controller. The superior performance of the SFL controller is demonstrated at varied operating conditions through frequency scanning analysis, eigenvalue analysis, and electromagnetic transient simulation. Moreover, the robust stability of the proposed controller is guaranteed under parameter uncertainties using μ analysis.

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This paper proposes a fractional-order sliding mode control (FOSMC) based on feedback linearization (FL) technique to mitigate subsynchronous control interaction (SSCI) in doubly fed induction generator (DFIG)-based wind farms connected to series-compensated transmission lines. A linearized form of the studied system is obtained with the use of FL, which leads to reduced system order and small computational burden. Then the FOSMC is designed for grid-side converter (GSC) to stabilize SSCI and to provide a considerable robustness against external disturbances and parameter uncertainties. For FOSMC parameter tuning, genetic algorithm (GA) is performed through MATLAB/SIMULINK. Time-domain simulation are carried out to evaluate the effectiveness of the FOSMC in mitigating SSCI at varied operating conditions, and the superior performance of the proposed control is demonstrated as compared with conventional vector control (VC), feedback linearization sliding mode control (FLSMC), high-order sliding mode control (HOSMC). KEYWORDS doubly fed induction generator, fractional-order sliding mode control, subsynchronous control interaction 1 | INTRODUCTION Subsynchronous resonance (SSR) of wind farms is a condition where wind turbines exchange energy with the grid at one or more natural frequency below the fundamental frequency. 1 A new type of SSR, known as subsynchronous control interaction (SSCI), has been detected worldwide in recent years. 2 Without the involvement of mechanical components, rapidly developing SSCI can lead to serious equipment damage and loss of power generation if proper countermeasures are not taken instantly. Furthermore, many studies have demonstrated that doubly fed induction generator (DFIG) wind farms are susceptible to SSCI due to the active participation of fast-acting converter control. 3,4 Therefore, it is urgent to develop effective SSCI mitigation techniques to ensure the safe operation of grid-connected DFIG-based wind farms.The design of SSCI damping controls has received much attention from industry and academia. A number of control methods using FACTS devices are proposed to mitigate SSCI, such as gate-controlled series capacitor (GCSC), 5 thyristor-controlled series capacitor (TCSC), 6 and static synchronous compensator (STATCOM). 7 As compared with FACTS-based damping controls, modification of wind turbine converter (WTC) control is an economical and convenient solution to SSCI. Since grid-side converter (GSC) has the damping capability similar to STATCOM with an extra advantage of lower cost, various damping methods are proposed based on the improvement of existing GSC control. A washout block is embedded into GSC stator voltage control for SSCI mitigation. 8 A supplemental damping signal is added to the summing junction of GSC's outer control. 9 GSC's d-axis inner control loop is also utilized to alleviate SSCI with speed deviation as input control signal (ICS). 10 GSC provides the greater flexibility of adding SSCI damping controls, but its damping capability is limited to 30% of...