## 1 Introduction  
Distributed energy resources (DER's) are an integral part of power systems as their inclusion is to reduce environmental pollution, improve system flexibility, reduce power losses, meet the load demands and increase system efficiency from economic and technical perspectives [1]. DER's (generally consist of solar plants, wind farms, mini hydro's turbines, biomass, fuel cell and geothermal energies) generate power at a smaller scale compared to conventional power resources, also refer as distributed generation (DG) [2]. However, excess DG inclusion in the power system and their unpredictable nature may lead to technical problems for the loads as well as DG itself. Some of the technical problems are unsynchronized relclosing, power quality issues, system security, maloperation of protection schemes, system stability and reliability, islanding and voltage regulation [2, 3, 4]. Unintended islanding condition is the one of chief alarming state from a technical viewpoint for power system operation. A fault is identified by the security scheme of the grid but not by DG protection scheme, failure operation of equipment, malpractices, an act via nature and human mistake are the main reason behind unintended islanding condition [5]. In the islanding situation, DG is still energizing the local load in response to grid supply disruption. Islanding is an unsolicited condition in a power system that originates safety concerns for workers, power quality issues for load and unsynchronized closure that harms generation and supply services [6]. A standard for islanding detection \"IEEE-STD 1547-2018\" acclaims that after the islanding situation, it must be identified within 2 s [7]. Islanding recognition strategies are generally divided into two types such as remote methods and local methods. Each islanding detection method is assessed via non-detection zone (NDZ). NDZ is a region or area where the protection schemes are unable to recognize islanding conditions [1,2,4]. Remote strategies are based on communication links or channels between DG and utility. This method has zero NDZ, no impact on power quality, fast response and reliability. However, this method is non-economical due to the extra transmitter and receiver employed in the distribution system and without employing backup protection [8,9]. Common techniques of this method are supervisory control data acquisition (SCADA), power line carrier communication (PLCC) and transfer trip [9]. Local methods are further split into three categories: active, passive and hybrid methods. Active methods are based on the distortion signal injection in the power system to measure the output parameter variation. In grid-connected mode, there is no significant variation in the parameter as the grid side absorbs these signals. However, during islanding mode, there is an extreme alteration in the output parameter and this alteration leads to the initiation of the protection scheme. Active methods have insignificant NDZ compare to passive techniques [2,8,10]. However, this method creates power quality issues for load [2,8]. Generally used active islanding detection techniques are Sandia frequency/voltage shift (SFS/SVS) [11], virtual capacitor/inductor [12,13], current injection [14], active frequency drift (AFD) [15], phase-locked loop (PLL) signal injection [16] and high frequency signal injection-based schemes [17]. Passive methods are based on the measurement of a local parameter such as frequency, voltage, THD, etc. at the point of interconnection (POI) [1]. Islanding situation only identified when measured parameter value exceeds the predefined threshold value, then the relay sends a trip signal to the breaker of the DG unit [1,4]. Passive methods are easy to implement, simple, economical and regardless of power quality issues [10,18]. However, large NDZ and difficulty in threshold selection are the main drawbacks of passive methods [10,19].