Case Studies for Non-Detection of Islanding by Grid-Connected In-Parallel Photovoltaic and Electrical Energy Storage Systems Inverters  
[PERSON]  
1 Photovoltatics Laboratory, New and Renewable Energy Institute, Korea Institute of Energy Research, Daejeon 34129, Korea; [EMAIL_ADDRESS] (J.R.L. ); [EMAIL_ADDRESS] (H.M.H. ); [EMAIL_ADDRESS] (W.G.S. ); [EMAIL_ADDRESS] (H.-S.); [EMAIL_ADDRESS] (Y.-C.J. ); [EMAIL_ADDRESS] (Y.S.J. ); [EMAIL_ADDRESS] (G.H.K.) 2 Department of Safety Engineering, Seoul National University Science and Technology, Seoul 01811, Korea Correspondence: [EMAIL_ADDRESS]; Tel. : +82-42-860-328  
As shown in Table 1, in Korea, the 'REC (Renewable Energy Certificate) weight 5.0' rule is operating to expand the grid linkage capacity for PV systems and to improve the stability of the power system by reducing fluctuations. And as shows Figure 1 this rule grants five times the REC weighting to the output electrical energy discharged from EESS after 4:00 p.m. when the EESS is charged by electrical energy produced by a PV system from 10:00 a.m. to 4:00 p.m. [20]. Power generation companies operating PV plants are planning to install EESSs linked to PV systems, and the demand for EESSs is expected to increase. The islanding of grid-connected distributed systems such as PV, EESS, and wind power occurs when a section of the utility system containing such distributed systems are disconnected from the main utility voltage source [22]. Anti-islanding papers given at the Institute of Electrical and Electronics Engineer (IEEE) conferences and published in journals have increased rapidly between 1989 and 2012: the number of published papers was six in 2002 and seventy-four in 2012. This shows that there is increasing interest in the detection of islanding [23; 24]. In addition, there is growing interest in the safety of micro-grid and distributed power systems regarding voltage and frequency variations [25; 26]. Distributed systems continue to feed the power utility lines in the isolated sections known as islands [27; 28]. Such isolated islands are dangerous to people who consider the load inactive and it cause serious accidents to power system at the next power-up [29]. In particular, operators may suffer serious problems when exposed to the island circuit during grid repair operations. Moreover, there is a risk of damage to the PV and EESS if the island is reconnected without synchronization [30]. Therefore, it is clear that the islanding situation requires proper control to perform a stable operation of distributed power systems [31]. The inverter of a distributed system has an algorithm (e.g., frequency detection method, reactive power injection-detection method) that can detect an isolated island [32]. In PV inverters, the methods used to detect islanding fall into three categories: passive islanding, active islanding, and remote \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Division** & **REC Weighted Value** & **Installation Type** & **Detailed Criteria** \\ \hline \multirow{5}{*}{Only PV System} & 1.2 & \multirow{2}{*}{If you are on regular grounds} & Less than 100 kW \\  & 1.0 & & From 100 kW \\  & 0.7 & & From 3000 kW \\ \cline{2-4}  & 1.5 & Using existing facilities & 3000 kW or less \\  & 1.0 & such as a building & From 3000 kW \\ \cline{2-4}  & 1.5 & Installing floats on the surface of the retainer & \\ \hline \multirow{2}{*}{PV System + EESS} & \multirow{2}{*}{5.0} & EESS (PV system connection) & \multirow{2}{*}{’16,’17, 18} \\  & & & \\ \end{tabular}
\end{table} 
Table 1: The Renewable Energy Certificate (REC) weights of a photovoltaic (PV) system and electrical energy storage system (EESS) in Korea [21]. Figure 1: Photovoltaic (PV) system + electrical energy storage system (EESS) Renewable Energy Certificate (REC) weight rule [20]. islanding. Among the most popular standards for anti-islanding are IEEE 929-2000, IEC62116, IEE1547, VDE0126-1-1, and AS 4777.3-2005. Table 2 shows each standard with its quality factor, required islanding detection time, normal frequency, and voltage operation range.