I. Introduction
Wind energy system integration into conventional grids is increasing rapidly worldwide. Being a very cost-efficient mechanism, several countries are introducing wind into future energy plans [1]. Because of the increased efficiency and cost effectiveness, Type-3 (Double-Fed Induction Generator) and Type-4 (Full Size Converter Machine) wind turbine generators (WTGs) are the most prevalent types of WTGs [2] and those are connected to the grid via power electronic converters. But integration of large-scale wind energy brings a set of operational and control challenges that impact on the grid reliability and stability [3]. One of the main issues of integrating wind energy into the grid is system strength. System strength is one determinant of how well the power system can return to normal operation following a disturbance or fault. To define system strength at the PCC, an index is widely used named Short Circuit Ratio (SCR). The SCR at the Point of Common Coupling (PCC) is the ratio of the PCC short circuit capacity to the rated power capacity of the generator. A minimum SCR value is required to ensure that network voltage remains stable and within a standard range after switching operations of the capacitors, reactors, and circuit, or if there are any variations in load or network disturbances [4]. A system is considered strong if its SCR is 3 or higher [5]. WTGs cannot provide large SCR values like conventional synchronous generators since the fault current contributed by WTGs is limited by power electronic converters [6]. As a result, system strength at the PCC declines.