1 Abstract—Increasing concerns about energy security and reliability are intensifying the interest in microgrid and vehicle- to-grid (V2G) technologies. Although the role of V2G technology within the context of optimal scheduling for larger grids has received much attention in the literature, its role within the regulation of microgrids has not yet been studied extensively. In this paper, we focus on the voltage and frequency regulation problem. We develop a microgrid model that is representative of the microgrid architecture considered in the SPIDERS (Smart Power Infrastructure Demonstration for Energy Reliability and Security) project of the Department of Defense. The model is parameterized to reflect the characteristics of Camp Smith, HI, the targeted installation of the SPIDERS project, and the long term Army goals regarding renewable energy penetration and reduction in fuel consumption. The model is augmented by power, frequency, and voltage control algorithms for the inverters that connect microsources to the microgrid. It also incorporates charging/discharging control algorithms for plug-in electric vehicles (PEVs) to take advantage of their capacity as both controllable loads and sources. Using this model, we study the impact of PEVs on the microgrid at different penetration levels and for different control parameters, with the aim of identifying the conditions needed for the vehicle-to-grid technology to have a positive impact on microgrid performance. Index Terms—Electric vehicles; frequency control; microgrid; vehicle-to-grid; voltage control I. INTRODUCTION Industrial and political plans to increase energy security, sustainability, and resilience require the stable and reliable integration of renewable resources and the effective use of the distributed energy storage capacity provided by the vehicle-to- grid (V2G) technology. Microgrids were proposed as an effective way to meet such requirements. The concept of a microgrid has been defined as an aggregation of loads and micro-sources operating as a single system that is seen as a single controlled unit by the total grid network [1]. Several kinds of power sources, such as wind, solar, geothermal, and fossil fuel, can be involved in electric power generation in microgrids. The intermittent characteristics of renewable power sources, as well as disturbances such as unplanned This work was supported by the Automotive Research Center (ARC), a U.S. Army center of excellence in modeling and simulation of ground vehicles. T. Ersal, C. Ahn, H. Peng, and J. L. Stein are with the Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109 USA (e-mail: {tersal, sunahn, hpeng, stein}@umich.edu). I. A. Hiskens is with the Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109 USA (e- mail: hiskens@umich.edu). islanding of the microgrid, may cause stability issues, and hence effective control and management of multiple power sources and storage devices becomes crucial. This paper considers voltage and frequency regulation in microgrids, and focuses specifically on the role of V2G technology in microgrid regulation. The small inertias of microgrids make the regulation problem more challenging, especially during islanding [1, 2]. Islanding may happen due to planned outages for maintenance, for example, but also due to unexpected failures in the main grid or the microgrid. Without appropriate short time-scale control, significant fluctuations in frequency and voltage can occur due to an imbalance between power supply and demand. Stable operation under such unexpected failures is crucial for applications where sustaining the critical loads is important for security or safety, and V2G technology could help achieve this goal. This work is at the intersection of two rapidly evolving technologies: V2G and microgrids. The impact of integrating vehicles into the grid in a large scale has received much attention in the literature [3-13]. Researchers have shown that the existing generation capacity can readily accommodate the penetration of plug-in electric vehicles (PEVs), if the PEV charging is carefully controlled [3]. More importantly, V2G technology could increase the integration of renewable power sources into the grid [5, 10, 12, 14, 15], reduce emissions [8, 10, 12, 16], help with ancillary services such as regulation, spinning reserves, and peak power [4, 5, 9, 14, 15, 17], thereby offering economic benefits [4, 9, 15, 17]. To achieve such goals, researchers have proposed and analyzed different control schemes [18-23]. Control techniques for other controllable loads such as thermostatically controlled loads [24] or other sources such as photovoltaic systems [25, 26] could also impact V2G systems [13, 25]. These V2G control approaches mainly focus on the scheduling problem within the context of large grids. Such optimal scheduling techniques typically focus on longer time- horizon performance and may thus not respond to sudden interruptions fast enough, which is critical for regulation of microgrids. The importance of regulation was recognized in the microgrid literature from the beginning, and researchers proposed various control methods, such as droop control [1, 27-31] or integral control of inverters [32], even though these earlier works did not explicitly consider V2G technology. Thus, the two bodies of literature grew initially independently. Recent work, however, started taking PEVs into account and proposed control methods for PEV charging/discharging based Tulga Ersal, Changsun Ahn, Ian A. Hiskens, Fellow, IEEE, Huei Peng, and Jeffrey L. Stein Impact of Controlled Plug-In EVs on Microgrids: A Military Microgrid Example