Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. DFIG-BASED WECS EFFECTS ON POWER SYSTEMS <s> Emphasis in this article is on the power system impact of wind power plants capability to provide enhanced ancillary services, i.e. temporary frequency response (TFR) and power oscillation damping (POD). The main objective of the article is to analyze and justify the challenges in the use of TFR and POD from wind power plants (WPPs). The study is conducted with an aggregated wind power plant model which is integrated into a generic power system model, specifically designed to assess the targeted ancillary services in a relatively simple, but still relevant environment. Various case studies with different wind power penetration levels are considered. <s> BIB001 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. DFIG-BASED WECS EFFECTS ON POWER SYSTEMS <s> Recently, the variable-speed wind turbine with doubly fed induction generator (DFIG) has drawn significant attention because of its many advantages such as small power converter rating, the ability to control the output power, etc. Nevertheless, the large penetration of DFIG wind turbines may affect the power system dynamics. This paper provides a general review of the DFIG wind turbine's impact on power system dynamic performances such as frequency stability, transient stability, small-signal stability, and voltage stability. Besides, ancillary services from the DFIG wind turbine for the power grid, such as frequency support, reactive power, and voltage support, are explained. Especially, the survey emphasizes power oscillation damping methods by the DFIG wind turbine. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. <s> BIB002
The DFIG effect on power system dynamics is divided into four main categories which are voltage stability, small-signal stability, transient stability, and frequency stability BIB002 . Voltage stability is defined as the capability of power systems to maintain nominal voltages at all buses after disturbances. DFIG based WECS can improve voltage stability with its ability to supply or absorb reactive power. The DFIG based WECS voltage recovery performance is better compared to an induction generator IG-based WECS with the same rating. Small-signal stability is known as the ability of power systems to insure synchronism under minor disturbances. Small signal instability can cause critical oscillations and rotor angle increase due to damping and synchronizing torques shortage. Transient stability is similar to small-signal stability, but it is concerned with serious disturbances. In the case of a dangerous disturbance like short circuit, the power system inertia and synchronizing torque are affected because the DFIG based-WECS inertia is decoupled with the power system. As a result, the total angular deceleration or acceleration takes place in the power systems synchronous generators. Frequency stability is the power system capability to preserve system nominal frequency under serious generation load unbalance. The DFIG based WECS power fluctuations may lead to frequency perturbations and reduce system inertia. Power system stability can be improved by wind WECSs which provide oscillation damping and temporary frequency response. However, coordination between them is necessary to avoid undesired stability degrade BIB001 . Figure 5 describes the power system and wind power plant transient frequency responses. The power system transient response can be seen from two intervals which are initial response and primary frequency control. The initial response illustrates the synchronous generators inertia response to the premier frequency variation. In the primary frequency control interval, the synchronous generators frequency droop controllers which have important effect on the final steady state frequency level and nadir are automatically enabled to settle down the system frequency to a new stabilization level. The wind power plant response is divided into three sections which are injection, decay, and recovery. During the injection phase, the wind power plant temporary supplies power to compensate for the grid frequency nadir. Through the decay period, the wind power plant output power gradually returns to its initial power level. Finally, the wind power plant output power enters a recovery phase where it stabilizes to its first power reference. Table 2 summarizes some of the research papers that are presented in this article and consider DFIG based WECS ancillary grid services like reactive power control, fault or voltage ride through, power quality improvement, frequency control, and power oscillation damping.