# LVRT and Stability Enhancement of Grid-Tied Wind Farm Using DFIG-Based Wind Turbine
## 1 Introduction
Therefore, depending on the potentiality to independently regulate the active and reactive power supplied to the grid, DFIG can provide better system stability during fault conditions over SCIG. Despite that, VSWT-DFIG based WFs are highly expensive due to the presence of partial rating power electronic AC/DC/AC converter, and that is the major disadvantage of VSWT-DFIG. Hence, the hybrid installation of small-scale VSWT-DFIG, including large-scale SCIG, can be an effective solution where it is possible to stabilize SCIG with the help of the reactive power control capability [6; 14]. Thus, the LVRT competency and stability of SCIG can be ensured at a lower cost. Many control techniques can be applied to the RSC and GSC of DFIG [20; 21; 22]. However, the design mechanism of the RSC controller is vital and crucial as it is controlling the active and reactive power. In consequence, some auxiliary circuitry has already been utilized to facilitate the DFIG to enhance the LVRT criteria. Illustrated by a crowbar circuit [17; 23], a new bridge-type of fault current limiter (NBFCL) [24], hysteresis current control [25; 26], dynamic voltage restorer (DVR) [27], superconducting magnetic energy storage (SMES) based AC-DC unified power quality conditioner (UPQC) [28], modified elephant-herding random forest algorithm (MEHRFA) technique [29], and a STATCOM are used to provide an adequate amount of reactive power during fault conditions to augment LVRT aptitude [30]. Using these devices [17; 23; 24; 25; 26; 27; 28; 29; 30], it is possible to stabilize the large-scale SCIG-based WF using its reactive power injection capability. However, this solution requires a high amount of storage components which makes the system more complex and increases the overall expenditure [24]. Some intelligent control techniques are also employed in the RSC of the DFIG system to improve LVRT, for example, fuzzy logic controller [31] and model predictive controller [32]. Although the LVRT competency can be improved, the computational burden for both of these controllers is high. Moreover, the success of the fuzzy controller mainly dependsupon past experience to design fuzzy rules of the designer. To conclude from the above literature reviews, it is better to design a simple and robust controller of DFIG instead of any auxiliary devices for both WT generators and intelligent control to augment the LVRT competency and capacity of grid-tied SCIG based WF. Thus, the prime contribution of this research is to design a new controller based on the PI controller to control the outer and inner loop of the RSC controller for the DFIG to augment LVRT functionality and enhance the capacity of SCIG based WFs. The outer loop for reactive power is controlled using a voltage-reactive power characteristics curve. The entire system was presented here, along with elaborate modeling and control techniques. Simulation studies were performed on an infinite bus power system network combined with large-scale FSWT-SCIG and small-scale VSWT-DFIG based WF to evaluate the efficacy of the proposed control strategy, and it was compared to that described in [33], which was comprised of a DFIG regulated by a conventional PI-based cascade control system. Therefore, the proposed control technique was found quite efficacious in enhancing LVRT capability and securing the stability of the power system. Furthermore, the installed SCIG's capacity could be increased. The remaining part of this paper was categorized as follows. Section 2 covered the design of the power system, Section 3 covered the design of the WT, Section 4 covered the DFIG designing and proposed cascaded RSC control system, Section 5 covered the simulation results and a discussion of the effectiveness of the proposed system over conventional methods. Finally, Section 6 illustrated the conclusions.