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Fast growth of wind power generation and its contribution in power systems dynamic performance has highlighted the importance of developing generic models for wind turbines. Following the former efforts, an enhanced version of standard generic wind turbine model is proposed in this article. The enhancements are aimed to make the model applicable for unbalanced Root Mean Square (RMS), short-term frequency stability, and low-voltage ride-through (LVRT) studies. Moreover, fidelity of the overall responses of the model is increased. To achieve these goals, five new blocks are designed and added to the base model and three existing blocks are modified. The new blocks are negative-sequence generator/converter model, inertial controller, LVRT controller, dc-link and the Line Side Converter (LSC), and the natural flux models. Responses of the enhanced model are compared with the results of both the base model and a detailed model, and validity of the proposed model is verified by different transient scenarios. [ABSTRACT FROM AUTHOR]

Wind turbine generators (WTG) can participate in system frequency regulation via virtual inertial controllers (VIC). In the presence of frequency disturbances, VIC temporarily regulates the WTG power output forcing it to release/absorb kinetic energy into/from the grid. With increasing penetration of WTGs in power systems, grid operators require these generators to provide frequency regulation services; however, kinetic energy release/absorption can destabilize WTGs. Hence, to address these issues, a new large-perturbation nonlinear WTG model is proposed in this paper, based on the WTG internal response that is used to tune typical VICs. Novel worst case and optimal VIC tuning approaches are also proposed and discussed based on the developed WTG nonlinear model. Several simulations are presented to test and validate the proposed model and VIC tuning techniques, demonstrating their adequate performance and advantages. [ABSTRACT FROM AUTHOR]

This study proposes a modified virtual inertial control (MVIC) scheme for doubly‐fed induction generator (DFIG)‐based wind turbines (WTs), which both improves the frequency response of these renewable resources and enhances the power system oscillation damping capabilities. It is shown that the proposed control structure enables the WT to participate prudentially in system frequency regulation, which means the amount of WT kinetic energy released to the grid and its participation in system frequency support is alleviated as its stored energy decreases. The proposed control strategy is introduced conceptually, and its performance is verified analytically. Effects of wind speed variations on the small‐signal stability of DFIG WTs equipped with the proposed MVIC is investigated, as well. For these purposes, the system characteristic equation and its damping ratio, as well as the transfer function between the wind speed and the wind turbine rotor speed are derived and analysed. Eventually, time‐domain simulation results and modal analysis verify the performance of the proposed method and demonstrate its superiority as compared to the conventional virtual inertial controllers. [ABSTRACT FROM AUTHOR]

This paper deals with the coordinated control of rotor- and grid-side converters in wind turbines with doubly fed induction generators (DFIGs) to improve the low-voltage ride-through capability. The rotor-side converter control and additional equipment, called stator damping resistor, are used to limit the rotor inrush current and to reduce the oscillations and settling time of DFIG transient response during the voltage dip. Also, the grid-side converter is controlled to limit the dc-link overvoltage during the voltage drop. It is found that the dynamics of the grid-side converter and dc-link voltage exhibit nonminimum phase behavior, and thus there is an inherent limitation on the achievable dynamic response during the fault. Since the dc-link dynamics is nonlinear, the linear control scheme cannot properly limit the dc-link voltage under large voltage dips. Thus, a nonlinear control scheme applied to the grid-side converter is proposed, which stabilizes the internal dynamics and limits the dc-link voltage fluctuations during the fault. The proposed ride-through approaches limit the peak values of rotor current and dc-link voltage at the instants of occurring and clearing the fault. They also limit the oscillations of electromagnetic torque, and consequently, improve the DFIG voltage dip behavior. [ABSTRACT FROM PUBLISHER]

This paper first discusses dynamic characteristics of wind turbines with doubly fed induction generator (DFIG). Rotor back electromotive force (EMF) voltages in DFIG reflect the effects of stator dynamics on rotor current dynamics, and have an important role on rotor inrush current during the generator voltage dip. Compensation of these voltages can improve DFIG ride-through capability and limit the rotor current transients. It is found that the electrical dynamics of the DFIG are in nonminimum phase for certain operating conditions. Also, it is shown that the dynamics of DFIG, under compensation of rotor back EMF and grid voltages, behave as a partially linearizable system containing internal and external dynamics. The internal and external dynamics of DFIG include stator and rotor dynamics, respectively. It is found that under certain operating conditions, the internal dynamics, and thus, the entire DFIG system becomes unstable. This phenomenon deteriorates the DFIG postfault behavior. Since the DFIG electrical dynamics are nonlinear; the linear control scheme cannot properly work under large voltage dips. We address this problem by means of a nonlinear controller. The proposed approach stabilizes the internal dynamics through rotor voltage control, and improves the dynamic behavior of the DFIG after clearing the fault. [ABSTRACT FROM AUTHOR]

Abstract: This paper analytically investigates the effects of system and controller parameters and operating conditions on the dynamic and transient behavior of wind turbines (WTs) with doubly-fed induction generators (DFIGs) under voltage dips and wind speed fluctuations. Also, it deals with the design considerations regarding rotor and speed controllers. The poorly damped electrical and mechanical modes of the system are identified, and the effects of system parameters, and speed/rotor controllers on these modes are investigated by modal and sensitivity analyses. The results of theoretical studies are verified by time domain simulations. It is found that the dynamic behavior of the DFIG-based WT under voltage dips is strongly affected by the stator dynamics. Further, it is shown that the closed loop bandwidth of the rotor current control, rotor current damping, DFIG power factor and the rotor back-emf voltages have high impact on the stator modes and consequently on the DFIG dynamic behavior. Moreover, it is shown that the dynamic behavior of DFIG-based WT under wind speed fluctuation is significantly dependent on the bandwidth and damping of speed control loop. [Copyright &y& Elsevier]

Abstract: This paper deals with the low voltage ride-through (LVRT) control of wind turbines with doubly fed induction generators (DFIGs) under symmetrical voltage dips. The investigation first develops a mathematical formula for the rotor current and rotor voltage when DFIG is subjected to a symmetrical voltage dip. From the analysis, the reasons of rotor inrush current and factors influencing it are inferred. Then, a control scheme enhancing the wind turbine LVRT capability is designed and simulated. The proposed control scheme consists of a nonlinear control strategy applied to the rotor-side converter and a dc-link voltage control applied to the grid-side converter. It improves the damping of DFIG transient response and minimizes oscillations of rotor current, electromagnetic torque and dc-link voltage during the generator voltage dip. It also limits the peak value of these quantities. At the end, results of theoretical analyses are verified by time domain simulations. [Copyright &y& Elsevier]

Abstract: This paper analytically investigates the dynamic behavior of fixed speed wind turbines (FSWTs) under wind speed fluctuations and system disturbances, and identifies the nature of transient instability and system variables involved in the instability. The nature of transient instability in FSWT is not similar to synchronous generators in which the cause of instability is rotor angle instability. In this paper, the study of dynamic behavior includes modal and sensitivity analysis, dynamic behavior analysis under wind speed fluctuation, eigenvalue tracking, and using it to characterize the instability mode, and investigating possible outcomes of instability. The results of theoretical studies are verified by time domain simulations. It is found that the instability occurs due to the mechanical dynamics and the instability is closely related to increasing of generator slip. [Copyright &y& Elsevier]