# LVRT and Stability Enhancement of Grid-Tied Wind Farm Using DFIG-Based Wind Turbine
## 1 Introduction  
Currently, it is even more evident that the significant burning of fossil fuels, price volatility, and rising awareness of environmental issues emphasized the importance of renewable and clean energy sources. Moreover, renewable energy sources are free, endless, clean, and readily available. With the installation of a 60.4 GW system in the wind industry, 2019 was a remarkable year as it was the second-biggest year in history. Moreover, the new installation introduced global cumulative wind power (WP) capacity up to 651 GW and represented year-over-year (YoY) growth of 19%. Furthermore, the global wind energy council (GWEC) estimated the addition of a new capacity for more than 355 GW over the next five years, with an annual installation of 71 GW until 2024 [1, 2]. Such an enormous integration of WP in the power grid has severe consequences for transient stability. Concerning the stabilization of the system, a wind turbine (WT) needs to satisfy the grid code criteria based on the network condition. Low voltage ride-through (LVRT) is one of the vital grid code requirements for the transient analysis [3]. However, as per the LVRT criteria, WF must not only stay connected with the grid but also provide reactive power to maintain grid voltage throughout faults [4]. Fixed-speed wind turbines with squirrel cage induction generators (FSWT-SCIGs) are the most frequently operated WTs as they are easy to construct, robust, and cost-effective [5]. Nevertheless, the SCIG is attached directly to the power grid and containsno LVRT functionality when the system is disrupted [6]. Since the voltage of a bus-connected FSWT-SCIG based WF drops dramatically, an adequate amount of reactive power is needed during the starting phase and short circuit fault [7]. The electromagnetic torque of SCIG is drastically reduced if a sufficient amount of reactive power is not injected. Hence, the SCIG rotor speed increases rapidly and therefore makes the power system unstable [8]. Generally, to supply reactive power, a capacitor bank is situated close to the SCIG terminals. Nevertheless, the SCIG needs a massive quantity of reactive power throughout the transient phase than the steady-state situation. The capacitor bank is failed to supply this large amount of reactive power during this period [9]. So that, to establish LVRT capacity and stabilize the terminal voltage, flexible AC transmissions (FACTs) devices including static synchronous compensator (STATCOM) [10], static var compensator (SVC) [11], superconducting magnetic energy storage (SMES) [12], energy capacitor system (ECS) [13], static synchronous series compensator (SSSC) [14], thyristor-controlled series capacitor (TCSC) [15] have been integrated with the SCIG. However, the cost of the system has increased. Instead, among different types of WT technology, variable-speed wind turbines with doubly fed induction generators (VSWT-DFIGs) have the most significant global market share due to their remarkable advantages, including lower converter rating and adjustable control, lightweight, high efficiency, output strength, excellent speed control, and decoupled ability to control active and reactive power [16; 17]. Additionally, full-scale power electronic converters are required for permanent magnet synchronous generators, whereas partial-scale power converters are required for DFIG-based systems [18]. All of these advantages are mostly owing to the control of the rotor-side converter (RSC), which is normally rated at about 30% of the generator rating whenever the rotor speed is within a range of 75% to 125% under normal operating conditions [19]. In VSWT-DFIG, the stator is directly coupled with the power grid, and the rotor is connected to the power grid via a back-to-back voltage source converter, consisting of an RSC and a grid-side converter (GSC). Both RSC and GSC regulate the amount of active power and reactive power dispatched.