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:

Maximum power point trackers (MPPTs) play an important role in photovoltaic (PV) power systems because they maximize the power output from a PV system for a given set of conditions, and therefore maximize the array efficiency. Thus, an MPPT can minimize the overall system cost. MPPTs find and maintain operation at the maximum power point, using an MPPT algorithm. Many such algorithms have been proposed. However, one particular algorithm, the perturb-and-observe (P&O) method, claimed by many in the literature to be inferior to others, continues to be by far the most widely used method in commercial PV MPPTs. Part of the reason for this is that the published comparisons between methods do not include an experimental comparison between multiple algorithms with all algorithms optimized and a standardized MPPT hardware. This paper provides such a comparison. MPPT algorithm performance is quantified through the MPPT efficiency. In this work, results are obtained for three optimized algorithms, using a microprocessor-controlled MPPT operating from a PV array and also a PV array simulator. It is found that the P&O method, when properly optimized, can have MPPT efficiencies well in excess of 97%, and is highly competitive against other MPPT algorithms.

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