0093-9994 (c) 2018 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/TIA.2018.2854622, IEEE Transactions on Industry Applications Survivability of Synchronous Generator-based Distributed Energy Resources for Transient Overload Conditions in a Microgrid Jongchan Choi Student Member, IEEE The Ohio State University Columbus, OH 43210, USA choi.1116@osu.edu Amrit Khalsa Senior Member, IEEE American Electric Power Groveport, OH 43125, USA askhalsa@aep.com David A. Klapp Member, IEEE Advanced Microgrid Systems Westerville, OH 43081, USA microgrids@outlook.com Mahesh S. Illindala Senior Member, IEEE The Ohio State University Columbus, OH 43210, USA millindala@ieee.org Karthikeyan Subramaniam Student Member, IEEE The Ohio State University Columbus, OH 43210, USA subramaniam.46@osu.edu Abstract–A synchronous generator-based distributed energy resource (DER) is commonly employed in microgrids due to its low cost and simple controls. However, there are many challenges to the DER operation when it is sized for supplying the critical loads alone in a microgrid. In particular, the DER would experience an overload condition during the microgrid transition from grid-connection to islanded operation, when the non-critical loads are also supplied momentarily. Therefore, it is very important to have a clear understanding on the survivability of a synchronous generator-based DER for transient overload conditions. Recently, experimental tests on survivability of the DER were carried out in the Consortium for Electric Reliability Technology Solutions (CERTS) Microgrid Testbed at American Electric Power. In this paper, an in-depth analysis of the synchronous generator-based DER operation during transient overload conditions is presented. The key relationships governing the system dynamic behavior of synchronous generator-based DER are analyzed to design the load shedding scheme for its survivability. Several case studies are illustrated to demonstrate the validity of the proposed load shedding method. Index Terms—Distributed power generation, islanding, load shedding, microgrids, overload conditions, power system protection, survivability, synchronous generators. I. INTRODUCTION Microgrids open several new avenues to resolve the numerous problems faced in modern power systems. Typically, a microgrid is formed by integrating distributed energy resources (DERs) and loads within a neighborhood [1]– [3]. Among the different DERs, the synchronous generator- based DER is most commonly utilized to supply electrical power due to its advantages such as simple control, stable operation, and cost effectiveness [4], [5]. However, the total capacity of synchronous generator-based DERs seldom cover the whole load in a microgrid [6]. Therefore, many challenges exist in their operation, especially when they are sized for only supplying the critical loads in a microgrid. Specifically, the synchronous generator-based DERs would experience an overload condition during the microgrid’s operational transition from grid-connected to islanded operation. Under-frequency load shedding is among the most reliable methods to protect the power system from outage [7], [8]. Many studies were published on improving its performance and application in a microgrid. A load shedding technique using both frequency and its rate of change (/) was proposed to deal with the frequency dynamics in the system when synchronous generators were tripped [9]. In [10] a self- healing scheme involving load-shedding was presented to handle a large disturbance in a power system. The estimation of the disturbance for an adaptive load shedding technique was proposed in [11]. It should be noted that these publications presented the under-frequency load shedding techniques activated by the status of system frequency; they did not provide information on its relationship with the operational limits of a synchronous generator-based DER. Renjit et al. discovered the prime-mover stalling phenomenon of synchronous generator-based DER in [12]. They found that the maximum power capability of a reciprocating engine driven synchronous generator-based DER is lowered when the prime-mover speed reduces with load change due to low inertia. The same condition in an inverter-based DER powered from a permanent magnet synchronous generator was reported in [13], [14]. The prime- mover stalling problem results from a sustained supply- demand energy imbalance in prime-mover driven DERs [12], [15]. In particular, a mixed source microgrid comprising both synchronous generator- and inverter-based DERs exhibited challenging frequency dynamics, which was investigated for various system disturbances in [16]–[18]. Furthermore, the prime-mover stalling phenomenon can This work was supported in part by the Office of Naval Research under Award N00014-16-1-2753 and the Office of Electricity Delivery and Energy Reliability, Transmission Reliability Program of the U.S. Department of Energy under subcontract 7004227 with The Ohio State University administered by the Lawrence Berkeley National Laboratory.