Active Islanding Detection with Parallel Inverters in Microgrid Sahil Gaurav Department of Electrical Engineering and Computer Science Indian Institute of Technology Bhilai Raipur, India-492015 sahilg@iitbhilai.ac.in Prashant Agnihotri Department of Electrical Engineering and Computer Science Indian Institute of Technology Bhilai Raipur, India-492015 pagnihotri@iitbhilai.ac.in Abstract—Distributed energy resources (DERs) connected to the main grid may experience unintentional islanding. The most widely used technique for islanding detection is the passive is- landing detection method. However, conventional passive methods have wider non-detection zone (NDZ) area. Failure to detect unintentional islanding events impose various issues like voltage & frequency instability, power quality degradation, protective devices malfunctioning, equipment damage, and threats to line workers. This paper presents active islanding detection for parallel inverters in AC microgrid in which the effects of d- axis and q-axis disturbance current injection are analysed and compared. Further, the outcomes of current injection at different parameters through multiple inverters have been shown and discussed. The simulation results of the active islanding detection are obtained using MATLAB/Simulink. Index Terms—Distributed generators, islanded microgrid, ac- tive islanding detection, current disturbance injection. I. I NTRODUCTION If an area of power system network is only receiving power by the local DERs through point of common coupling (PCC) and separated from rest parts of network, then that area of network is in islanding condition. This islanding can be categorized as: • Intentional Islanding • Unintentional Islanding Intentional islanding is a pre-planned islanding done by the power grid authority to do some maintenance or, fault clearing work. Therefore, it does not harm the power system. While unintentional islanding is like an accidental islanding which happens due to false tripping of circuit breakers, therefore it can harm the power system and line workers. This leads the unsynchronisation of DER with grid and subsequently DER supplies power to the loads at undesired range of frequency and voltage. The electrical equipments may get damaged due to unrated voltage and frequency. It can also harm the line workers because they cannot noticed that DER is supplying power in case of islanding situation [1], [2]. According to IEEE 1547 standard, it is necessary to detect unintentional islanding within 2 sec time framework, and all DERs are mandated to cease power supply as soon as islanding is detected [3]. There are primarily two detection methods for islanding identification as shown in Fig. 1: Fig. 1. Different methods of islanding detection The remote based islanding detection methods are based on either communication or, signal processing techniques. These methods are not preferred generally because of higher cost and complexity nature. The passive based islanding detection methods detect islanding by observing the output parameters of system. However, most of the passive based islanding detection methods have large NDZ area. The condition when DER’s output power is approximately equal to the demand of load is called NDZ condition. A. Non-Detection Zone According to IEEE 1547 standard, all DERs are to be provided with under/over voltage and frequency relays. Range of set point for voltage relays is within (1.1 pu to 0.88 pu) and the range of set point for frequency relays is within (60.5 to 59.3) Hz for 60 Hz system. In the case of islanded microgrid, active power mismatches leads to voltage deviations and reactive power mismatches leads to frequency deviations. However, if in the case that there is not much power difference between generation and demand, the relays fails to operate. Then this condition is called NDZ condition. B. State of the art methods and gaps in the existing active islanding detection techniques Several islanding detection methods have been presented in the past like feedback-based passive islanding detection technique (IDT) [4] which is solely developed for the one cycle control (OCC) inverter which is usually of small capacity. In [5], a novel IDT is developed based on the observation of derivative of equivalent resistance seen from the DER 978-1-6654-2873-6/21/$31.00 © 2021 IEEE 2021 9th IEEE International Conference on Power Systems (ICPS) | 978-1-6654-2873-6/21/$31.00 ©2021 IEEE | DOI: 10.1109/ICPS52420.2021.9670356 Authorized licensed use limited to: INDIAN INSTITUTE OF TECHNOLOGY GUWAHATI. Downloaded on February 13,2022 at 09:11:34 UTC from IEEE Xplore. Restrictions apply.