Voltage balancing and synchronization of microgrids with highly unbalanced loads N.W.A. Lidula a,n , A.D. Rajapakse b,1 a Department of Electrical Engineering, Faculty of Engineering, University of Moratuwa, Moratuwa 10400, Sri Lanka b Department of Electrical and Computer Engineering, University of Manitoba, 75 Chancellor's Circle, Winnipeg, MB, Canada R3T 5V6 article info Article history: Received 3 January 2013 Received in revised form 26 November 2013 Accepted 29 December 2013 Available online 24 January 2014 Keywords: Frequency and voltage control Microgrid synchronization Synchrocheck relay abstract Microgrids can operate in parallel with the grid or as a power-island. They are thus, expected to perform seamless transition from islanded to parallel operation and vice versa. This paper reviews the existing DG interconnection standards for microgrid resynchronization, investigates possible simple solutions for voltage balancing, and shows that the existing synchrocheck relay with a circuit breaker is sufficient to reconnect an islanded, highly unbalanced microgrid back to the utility grid. & 2014 Elsevier Ltd. All rights reserved. Contents 1. Introduction ........................................................................................................ 907 2. Review on microgrid synchronization and voltage balancing ................................................................. 908 2.1. Active synchronization ......................................................................................... 909 2.2. Passive synchronization......................................................................................... 910 2.3. Open-transition transfer synchronization........................................................................... 911 2.4. Voltage balancing in microgrids .................................................................................. 911 2.5. Summary of review on synchronization and voltage balancing in microgrids .............................................. 911 3. The microgrid test system............................................................................................. 911 4. Microgrid frequency and voltage control ................................................................................. 912 4.1. Standards .................................................................................................... 912 4.2. Microgrid control strategy....................................................................................... 912 4.2.1. Synchronous generator control ............................................................................ 912 4.2.2. Wind turbine control .................................................................................... 913 4.2.3. VSC with PI control ..................................................................................... 913 4.2.4. Load shedding ......................................................................................... 913 4.2.5. Switched capacitor bank for voltage balancing ............................................................... 914 5. Analysis of passive synchronization through simulations .................................................................... 914 5.1. Model validation .............................................................................................. 914 5.2. Role of switched capacitor banks in synchronization ................................................................. 915 5.3. Impact of synchrocheck relay settings ............................................................................. 918 6. Conclusions ........................................................................................................ 920 Acknowledgements ...................................................................................................... 920 References ............................................................................................................. 920 1. Introduction Historically, power has been provided by centralized generation via transmission lines to regional distribution substations. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/rser Renewable and Sustainable Energy Reviews 1364-0321/$ - see front matter & 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.rser.2013.12.045 n Corresponding author. Tel.: þ94 116 503 01x3203; fax: þ94 112 650625. E-mail addresses: lidula@elect.mrt.ac.lk, lidula@gmail.com (N.W.A. Lidula), Athula.Rajapakse@ad.umanitoba.ca (A.D. Rajapakse). 1 Tel: þ1 480 1403; fax: þ1 204-474 7522. Renewable and Sustainable Energy Reviews 31 (2014) 907–920