Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> 2) ADDITIONAL FREQUENCY SUPPORT FROM DFIG SYSTEM <s> This paper addresses the design and implementation of a novel control scheme for a doubly fed induction generator (DFIG), of the type employed with wind turbines, to provide support to power system operation. It is shown that this controller provides a DFIG-based wind farm with operational and control compatibility with conventional power stations, the ability to contribute to voltage support and recovery following network faults, the ability to provide a power system stabilizer capability that improves overall system damping, and the capability of contributing short-term frequency support following loss of network generation. A simple but realistic test network that combines synchronous and wind farm generation has been modeled and used to assess dynamic performance. Simulation results are presented and discussed that demonstrate the capabilities and contributions of the new DFIG controller to network support. <s> BIB001 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> 2) ADDITIONAL FREQUENCY SUPPORT FROM DFIG SYSTEM <s> The increasing penetration of variable-speed wind turbines in the electricity grid will result in a reduction of the number of connected conventional power plants. This will require changes in the way the grid frequency is controlled. In this letter, a method is proposed to let variable-speed wind turbines emulate inertia and support primary frequency control. The required power is obtained from the kinetic energy stored in the rotating mass of the turbine blades. <s> BIB002 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> 2) ADDITIONAL FREQUENCY SUPPORT FROM DFIG SYSTEM <s> An assessment on the capability of a doubly fed induction generator (DFIG) wind turbine for frequency regulation is presented. Detailed aerodynamic, structural and electrical dynamic models were used in this study. A control loop acting on the frequency deviation was added to the inertia contributing loop in order to enhance the inertia support from the DFIG wind turbine. The possibility of de-loading a wind turbine to provide primary and secondary frequency response was discussed. A frequency droop controller was examined where the droop is operating on the electronic torque set point below its maximum speed and is operating on the pitch demand at maximum speed. It is also shown that by reducing the generator torque set point the DFIG wind turbine can provide high frequency response. <s> BIB003 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> 2) ADDITIONAL FREQUENCY SUPPORT FROM DFIG SYSTEM <s> The paper investigates contribution of doubly fed induction generator (DFIG) to system frequency responses. Impact of different governor settings and system inertia are investigated. Three distinct cases are simulated in order to illustrate the influence of DFIG penetration on frequency regulation. Provision of inertial response by DFIG through artificial speed coupling is also presented. The effects of the inertial response on the machine behavior and its significance for frequency regulation are discussed. The influence of converter current limits and auxiliary loop parameters on the inertial response are illustrated and a novel control algorithm is developed for extracting maximum energy from the turbine in a stable manner. The results of the study are illustrated on the example of an isolated power system consisting of a diesel generator and a DFIG. <s> BIB004 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> 2) ADDITIONAL FREQUENCY SUPPORT FROM DFIG SYSTEM <s> As the penetration level of wind power in a power system increasing, it is required that the wind turbine generator should have the similar characteristics as the conventional synchronous generators to ensure the safety and stability of the power grid. Conventional generators provide frequency support to the grid in the way of inertial response, primary and secondary frequency regulation. However, the doubly fed induction generators (DFIGs) do not have the desired ability since they integrate into the system through the control of power electronic converters. This paper proposes a new control strategy to improve the DFIG's ability of frequency support based on the coordinated control of the wind turbine and the energy storage (ES) system. This strategy could provide better performance of frequency support and overcome the problems such as system frequency oscillation and secondary frequency drop. The proposed control strategy can be realized in all wind speed conditions with small scale of ES system. <s> BIB005 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> 2) ADDITIONAL FREQUENCY SUPPORT FROM DFIG SYSTEM <s> In order to meet power needs, with concern for economics and environment, wind energy conversion is gradually gaining interest as a suitable source of renewable energy. To maximize the power extraction from the wind, optimization techniques are used at the various module of a wind farm starting from wind farm design for siting, sizing, optimal placement and sizing of distributed generation (DG) sources, generation scheduling, tuning of PID controller, control of wind energy conversion system (WECS) etc. This paper mainly focuses on the optimization algorithms (mostly the swarm based) in relation to integration of the wind farm with the grid. The paper here gives a precise idea about different optimization techniques, their advantage and disadvantage with respect to a wind farm. This review will enable the researchers to open the mind to explore possible applications in this field as well as beyond this area. <s> BIB006 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> 2) ADDITIONAL FREQUENCY SUPPORT FROM DFIG SYSTEM <s> This paper presents a new wind farm control framework for inertial and primary frequency response for a high wind integrated power system. The proposed architecture is unique in the sense that the methodology can be used for frequency regulation support during subsynchronous and super-synchronous operation of the wind turbines (farm). The architecture work with existing wind farm controllers thus avoiding any additional replacement or tuning. The methodology depends on reduced order modeling based on model order reduction (MOR) and subsequent online controller design. The approach is tested on a smaller wind farm and further evaluated on a larger reduced power grid with 39 buses and ten generators. The results show that the proposed architecture provides greater flexibility in wind farm control towards frequency oscillations. <s> BIB007 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> 2) ADDITIONAL FREQUENCY SUPPORT FROM DFIG SYSTEM <s> 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 C P - 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. <s> BIB008 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> 2) ADDITIONAL FREQUENCY SUPPORT FROM DFIG SYSTEM <s> In a high penetrated wind farm power system, wind farms can collaborate to control the power system frequency as like as conventional units. This paper presents a novel model to control the frequency of the wind farm connected to conventional units. Throughout the proposed frequency control, the integral controller, washout filter, and the PID controller could determine the active power variation value in different situations. In fact, a PID controller makes the wind farm aware of power variations. To improve the efficiency of the model, the defined frequency control parameters (i.e., PID coefficients) are optimized based on a multiobjective function using particle swarm optimization algorithm. This study has a unique perspective based on the wind farm collaboration through inertia control, primary frequency control, and supplementary frequency control of the system. A swift power reserve in a stable condition is needed in which wind farm can ameliorate the system frequency response. It is worth saying that the wind farm consists of variable speed turbines, such as a doubly fed induction generator, or a permanent magnet synchronous generator. To assess the performance of the proposed model, it is applied to a typical two-area system and the results are compared. <s> BIB009
The DFIG system has the ability to support the system frequency variations by changing its inertial response by adjusting its rotational speed and electromagnetic torque. Since the DFIG has very small inertial response, the frequency nadir following a loss of generation can be significantly reduced. Important factors like current ratings limit the possible inertial response of DFIG. The response of a DFIG wind turbine for a frequency change can be explained using the torquespeed curves shown in Figure 15 . When the generator speed is reduced due to frequency decreased, decelerating torque is induced. Also, the generator aerodynamic torque increases while the electromagnetic torque is reduced. The DFIG system can be under loaded by changing the maximum power curve operating point. An increase in the rotor speed will increase the kinetic energy of the rotating mass. As a result, the frequency support provided to the network is decreased. A control strategy can be found in BIB002 . On the other hand, a decrease in the rotor speed will result in an increase in the kinetic energy given to the network which leads to a higher frequency support level. Factors such as the rotor maximum speed must not be exceeded in DFIG frequency support. Many research articles address the DFIG frequency control. For instance, BIB001 reports that long-term reset time can be countered using flux magnitude and angle controller (FMAC), and it is compared with classical synchronous generator control. Other study BIB005 proposes a control method that integrates energy storage system, FIGURE 15. DFIG torque-speed curves BIB003 . approximately 10% of the generator ratings, with DFIG for frequency support. The paper BIB004 investigates the influence of DFIG penetration on frequency regulation in terms of artificial speed coupling, inertial response on the machine behavior, and impact of converter current limits and auxiliary loop parameters. A technique that is based on model order reduction (MOR) and subsequent online controller design for primary frequency and inertial responses is presented in BIB007 . A primary frequency control method based on using pitch angles is proposed in BIB008 . This method adjusts the mechanical power such that the power over frequency droop demand of the primary frequency response is contented. Another important aspect is tuning the controller gains. For instance, BIB009 considers tuning the PID controller gains using particle swarm optimization algorithm (PSO) to improve the frequency control by DFIG WECS. Additional optimization methods that can be used for turning the DFIG's controllers gains are presented in BIB006 .