A Novel Hybrid Islanding Detection Method combination of SMS and Q-f for Islanding Detection of Inverter- Based DG Shahrokh Akhlaghi Department of Electrical Engineering Islamic Azad University Islamshahr Branch, Islamshahr, IranShahrokh.akhlaghi@gmail.com Ali Asghar Ghadimi Department o Electrical Engineering Arak University, Arak Iran a-ghadimi@araku.ac.irdesired Arash Akhlaghi Department of Electrical Engineering Islamic Azad University Islamshahr Branch, Islamshahr,Iran Akhlaghi.arash@yahoo.com Abstract—In this paper a novel hybrid method for islanding detection of inverter- based distributed generation is proposed. This algorithm which is a combination of Slip mode frequency- shift (SMS) and reactive power versus frequency (Q−f) as active methods detects the islanding phenomena by forcing the DG lose its stable operation and drift the frequency out of the allowed normal range of the frequency relays. A simple passive islanding detection scheme that relies on frequency relays such as under/over frequency protection (UFP/OFP) would be sufficient to detect the moment of islanding. For demonstrating the performance of the proposed method, it is evaluated under the IEEE 1547, UL 1741 anti-islanding test configuration and multiple-DG operation. The studies reported in this paper are based on time-domain simulations in the MATLAB/Simulink. The proposed hybrid method detects islanding more efficiently for loads with high quality factor (Qf); also it operates accurately in condition of load switching and does not interfere with the power system operation during normal conditions. Simulation results prove that the proposed method decreases the time of islanding detection and has less Non Detection Zone in comparison to previous methods. In addition, the technique represents to be robust under multiple-DG operations. Keywords—Distributed generation (DG), inverter, islanding detection, non-detection zone, Slip Mode frequency Shift (SMS). NOMENCLATURE DG Distributed Generation SMS Slip Mode frequency Shift IDM Islanding Detection Method DC Direct Current NDZ None Detection Zone PCC Point of Common Coupling UFP Under Frequency Protection OFP Over Frequency Protection R g , L g Resistance and Inductance of power system line R, L, C Load Resistance, Inductance and Capacitance L filter Inductance of the inverter filter k P , k I Proportional and Integral control factors θ SMS Phase angle for SMS method θ m Maximum phase angle in degree f Frequency f g Grid frequency f m Frequency at which θ m occurs f is Islanding frequency Q f Quality factor i d , i q d−q components of the current v d , v q d−q components of the Point of Common Coupling voltage. i dref , i qref Reference current of d-q components v dref , v qref Reference voltage of d-q components SPWM Sinusoidal Pulse width modulation m Modulation index amplitude φ Phase angle I. INTRODUCTION Islanding is a condition in which a portion of the utility system that contains both load and distributed resources remains energized while isolated from the remainder of utility system [1]. This process can occur due to preplanned or intentional and accidental or unintentional events. The accidental or unintentional islanding of distributed generation (DG) which can occur due to faults could cause negative impacts on distribution systems such as power-quality problems, equipment damage and even it can be dangerous to utility workers, who may not realize that a circuit is still powered. Also it may prevent interference of grid protection devices and automatic re-connection. Therefore, islanding must be rapidly detected within acceptable durations and then the circuit breaker between the power system and the distributed generation should be immediately tripped, this is referred to as anti-islanding [2]. As highlighted in the IEEE Std 1547-2003 and IEEE Std 929-2000, unintentional islanded DG systems require to be shut down within a predefined time period. Hence, one of the most technical challenges associated with distributed generation operation is islanding detection. The main philosophy of detecting an islanding situation is monitoring the DG output parameters and system parameters such as voltage amplitude, phase difference and frequency variation and then deciding whether or not an islanding 978-1-4799-4881-9/14/$31.00 ©2014 IEEE