0885-8977 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TPWRD.2016.2601921, IEEE Transactions on Power Delivery Abstract— In this paper, an adaptive directional overcurrent relaying technique based on the positive-sequence (PSQ) and negative-sequence (NSQ) superimposed currents is proposed for microgrid protection. Due to the change in mode of operation of microgrid, the level and direction of prefault current are altered. On occurrence of a fault in any line section of the microgrid, coordination between the primary and backup overcurrent relays is lost due to variations in level and direction of fault current. With inception of faults, the current contributed by the inverter based distributed energy resource (IBDER) is in the range of 2 p.u. To solve protection coordination issue, this paper presents an adaptive overcurrent relay settings using PSQ and NSQ superimposed currents those are contributed during fault conditions. Further, the direction of the fault is obtained using the new phase change between prefault and superimposed sequence fault currents. The proposed technique is implemented on a dSPACE processor board, which is connected to a Real- Time Digital Simulator (RTDS) to carry out the hardware-in-the- loop (HIL) test. Extensive simulation and hardware results obtained for several microgrid operating modes indicate the effectiveness of the proposed technique. This proposed approach is independent of the voltage information. Index Terms— Distributed energy resources (DERs), dSPACE processor, microgrid protection, mode of operation, real-time digital simulator (RTDS), superimposed sequence components. I. INTRODUCTION ith the increase in power demand over the years, penetration of distributed energy resources (DERs) such as photovoltaics (PVs), wind turbines, fuel cell and micro turbines are attractive options for various advantages such as reducing CO 2 emission, energy cost saving, reduced line cost and better system reliability [1]. However, integration of these DERs to the power network creates certain issues which need to be considered in order to facilitate the smooth operation of the microgrid. Directional overcurrent relays (DOCRs) based protection scheme for microgrid is one of the important techniques for the protection of such systems. For reliable and correct operation of DERs in the microgrid, the protection issue needs to be analyzed and solved. The performance of DOCR is dependent on current magnitude and phase angle between the polarizing and operating quantities. Due to grid- connected and islanded modes of operation of microgrid, there is a change in level and direction of both prefault and fault currents. Further, the fault current is clamped to 2-3 p.u of the rated current in case of inverter based distributed energy resources (IBDERs) [2]-[3]. Therefore, traditional DOCR settings are affected due to the different microgrid operating modes, penetration level, location and type of DERs present in microgrid system [4]-[16]. Magnitude and direction of fault current flowing through the line are also altered in the process of implementing the smart activities like active network management solutions for microgrid operation, circuit breaker status information, demand side management, power flow control, automatic restoration and the intentional/unintentional islanding operation [4]. Due to these smart operations, the coordination between the DOCRs is lost and dependability and selectivity properties are sacrificed. Consequently, there are chances of losing healthy sections instead of separating the faulted sections present inside a microgrid. In order to overcome the protection coordination problems in the microgrid, researchers have proposed several adaptive techniques for DOCRs [4]-[14]. In [5], an adaptive overcurrent protection technique is proposed by calculating the three-phase fault current at the relay bus for the changed system topology. In this work, online estimation of the Thevenin equivalent voltage and impedance at a particular relay bus is necessary. In [6], authors have estimated suitable overcurrent relay settings by adapting the steady state fault current for a reduced network at the fault point (FP). An adaptive DOCR technique based on the instantaneous-time overcurrent characteristics is proposed in [7] to protect the lines of a microgrid by detecting the islanding mode of operation with help of average rate of change of voltage. In [8], a scalable and fast method is reported to update the off-line calculated settings for overcurrent relays using a communication link with the information of the islanded mode of operation. In [9], calculated system impedance changes the relay settings adaptively for both grid-connected and islanded modes of operation of microgrid that is powered by IBDERs only. A multi-agent based technique is suggested in [10] to coordinate between different overcurrent relays which are installed in the microgrid, and other equipment. A protection method using the communication link existing between the sending and receiving end relays is proposed to protect the microgrid during the normal and high impedance fault (HIF) periods [11]. In [12], an adaptive overcurrent relaying scheme is provided by dividing the microgrid into different zones which act as a single islanded area. In [13], the technique Superimposed Adaptive Sequence Current Based Microgrid Protection: A New Technique Harikrishna Muda, Student member, IEEE, and Premalata Jena, Member, IEEE W Authors are with the Department of Electrical Engineering, Indian Institute of Technology, Roorkee, India-247667. Email- harikrishnam2@gmail.com and pjenafee@iitr.ac.in.