High-Speed Algorithm for Renewable Energy Based Microgrid Fault Detection and Protective Coordination Hashim A. Al Hassan 1 , Qiang Fu 2 , Vijay Bharavaju 2 , Yi Yang 2 , and Brandon M. Grainger 1 Electric Power Systems Laboratory – University of Pittsburgh Swanson School of Engineering; Pittsburgh, PA; USA 1 Eaton – Corporate Research and Technology, Menomonee Falls, Wisconsin; USA 2 haa20@pitt.edu / bmg10@pitt.edu Abstract— The microgrid concept was proposed as a way to facilitate the integration of distributed renewable energy resources. However, due to the use of distributed energy resources (DERs) microgrids face new protection challenges that need resolved. One of those challenges is that traditional protection methods, such as overcurrent protection, cannot be used mainly because of low fault currents, bi-directionality of power flow, and IEEE 1547 voltage ride-through requirements at the point of common coupling (PCC). Therefore, fault current and voltage magnitudes cannot be used as the protective indicators as they may cause breaker misoperation or longer trip times resulting in longer times to clear a fault. Additionally, knowledge of the fault location is a necessary element to properly protect the microgrid and avoid blinding or nuisance tripping. Change in the phase difference between voltage and current is an affective indicator that manifests on a short circuit in an islanded microgrid with inverter-based DERs. This paper explores the use of such an indicator and uses it as a foundation to propose a novel high-speed fault detection and fault direction detection method. A protective coordination algorithm is also proposed. The performance of the proposed solution is demonstrated in the PSCAD/EMTDC simulation environment. Keywords— Distributed energy resources (DERs), fault detection, fault location, microgrid, phase measurement, system protection, voltage ride-through. I. INTRODUCTION Protection is one of the most critical and challenging problems when it comes to microgrid systems especially when the microgrid is islanded. This is due to the limited current contribution from inverter-based sources, the bi-directionality of power flow, and the different modes of operation that require dynamic protection methods. Traditional over-current protection is not a reliable method when it comes to protecting the microgrid due to lower available source currents resulting in longer trip times [1-2]. Most methods in the literature depend on differential protection and a communication system in order to achieve this objective which can be slow and costly [1-3]. Relying on communication degrades the reliability because the system becomes more prone to a single point of failure. Others have used sequence components, which fails in detecting balanced three-phase faults and is unreliable in the case of unbalanced conditions [2], [4]. Some have used data mining approaches along with the differentials which are complex methods and also depend on communication [5]. The same is true for traveling wave based approaches [6-7]. Wavelet analysis has been proposed in [8] and has not been validated. In [9], the authors have added a flywheel in the microgrid in order to boost up fault currents and use traditional over-current protection. This method is costly and depends on the availability of the flywheel. A combination of different approaches have been proposed in [10] with differential protection as the main strategy. This method is costly and slow since it relies on other mechanisms as backup. In this paper, an alternative scheme will be explored in order to protect the microgrid. Specifically, the scheme will overcome the issues of low fault levels and bi-directionality of power flow that may cause blinding, nuisance tripping, or longer tripping times. This alternative cannot be based on voltage levels because renewables have to meet low-voltage and high-voltage ride through requirements (IEEE 1547). Detecting the relative fault location with respect to the protective element is critical to deal with the bi-directionality of power flow and to perform proper protection coordination. If this objective is achieved along with detecting the fault with good reliability and speed, microgrid protection becomes manageable. The most practical method to achieve this is using directional relays. However, traditional high-speed directional relays depend on high fault currents and determine the direction of current in 20 ms [11], which is not fast enough in order to reliably protect the microgrid weak sources. In this paper three main goals will be accomplished. These include: One, to justify the use of phase change between voltage and current as the main indictor to detect faults and relative location (fault direction) to properly operate a circuit breaker (CB). Two, utilize this indictor (phase change) and develop an approach to identify the direction of the fault and coordinate between circuit breakers faster than traditional high- speed directional relays. In this case, phase detection will be processed faster by exploiting all of the phase voltage of the three phase system in both half-cycles. A method to extract the fastest and the second fastest detection from the different signals is also developed. Finally, the indicator is implemented in a protective coordination algorithm. II. PROPOSED FAULT DETECTION AND FAULT DIRECTION DETECTION BASIC PRINCIPLE A. System Configuration for Investigation Correct modeling of the microgrid system under faults is critical in our investigation in finding an indicator for fault detection and relative location. The microgrid system that is 978-1-5090-2998-3/17/$31.00 ©2017 IEEE 519