This report describes the various methods and circuits that have been developed to detect an islanding condition for photovoltaic applications and presents three methods that have been developed to test those methods and circuits. Passive methods for detecting an islanding condition basically monitor parameters such as voltage and frequency and/or their characteristics and cause the inverter to cease converting power when there is sufficient transition from normal specified conditions. Active methods for detecting the island introduce deliberate changes or disturbances to the connected circuit and then monitor the response to determine if the utility grid with its stable frequency, voltage and impedance is still connected. If the small perturbation is able to affect the parameters of the load connection within prescribed requirements, the active circuit causes the inverter to cease power conversion and delivery of power to the loads. The methods not resident in the inverter are generally controlled by the utility or have communications between the inverter and the utility to affect an inverter shut down when necessary. This report also describes several test methods that may be used for determining whether the anti-islanding method is effective. The test circuits and methodologies used in the U.S. have been chosen to limit the number of tests by measuring the reaction of a single or small number of inverters under a set of consensus-based worst-case conditions. FOREWORDThis report has been prepared as part of Sandia National Laboratories' Photovoltaic Systems Research and Development work for the U.S. Department of Energy. Sandia is the DOE's lead laboratory for photovoltaic systems research. The development and approach for accomplishing meaningful systems goals for the nation's photovoltaic program and the photovoltaic industry is defined through five technical objectives: (1) reduce the life-cycle costs; (2) improve the reliability; (3) increase and assure the performance and safety of fielded systems; (4) remove barriers to the use of the technology; and (5) support market growth for commercial U.S. photovoltaic systems. This evaluation of the various islanding detection methods for photovoltaic inverters and utility-interactive power systems complements Sandia's photovoltaic inverter development and evaluation goals, provides valuable information for standards and codes input, and summarizes the strengths and weaknesses of the developed anti-islanding methods available today. ABSTRACTThis report describes the various methods and circuits that have been developed to detect an islanding condition for photovoltaic applications and presents methods that have been developed to test those methods and circuits. The methods described are separated into three categories. They are:

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Many methods for detecting and preventing islanding of photovoltaic and other distributed energy resources (DERs) have been proposed. However, in general, all anti-islanding systems that are based in the inverter have a "non-detection zone" (NDZ), which is a range of loads that defeat that anti-islanding mechanism.One alternative is to use power line carrier communications (PLCC). In this work, a PLCC-based anti-islanding system that works with a commercially-available automatic meter reading system is explored. Initial experimental results on this PLCC anti-islanding system are presented.The effectiveness of PLCC-based islanding prevention is discussed, and conclusions about this method are offered.

This white paper focuses on "advanced microgrids," but sections do, out of necessity, reference today's commercially available systems and installations in order to clearly distinguish the differences and advances. Advanced microgrids have been identified as being a necessary part of the modern electrical grid through a two DOE microgrid workshops, 1 ' 2 the National Institute of Standards and Technology, 3 Smart Grid Interoperability Panel and other related sources. With their grid-interconnectivity advantages, advanced microgrids will improve system 4 energy efficiency and reliability and provide enabling technologies for grid-independence to end-user sites. One popular definition that has been evolved and is used in multiple references is that a microgrid is a group of interconnected loads and distributed-energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid. A microgrid can connect and disconnect from the grid to enable it to operate in both grid-connected or island-mode. Further, an advanced microgrid can then be loosely defined as a dynamic microgrid. The value of microgrids to protect the nation's electrical grid from power outages is becoming increasingly important in the face of the increased frequency and intensity of events caused by severe weather. Advanced microgrids will serve to mitigate power

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