Authors:	Bower, Ward (1) Ropp, Michael (2)
Organizations:	Sandia National Laboratories Photovoltaic Systems Research and Development Albuquerque, NM, 87185-0753, USA (1) South Dakota University, Electrical Engineering Department HH205, Brookings, SD 57007-2220, USA (2)
Type:	Report IEA  PVPS Task 5
Reference:	IEA  PVPS T5-09: 2002
Date of issue:	March 2002
Details:	57 p.: figures, graphs; with references and glossary
Download:	Open or download this report as PDF document (1413 kB)
Available from:	Task 5 members or Operating Agent of Task 5
Abstract:	Passive methods for detecting an islanding condition basically monitor selected parameters such as voltage and frequency and/or their characteristics and cause the inverter to cease converting power when there is a transition from normal grid-connected 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.
	This report describes a broad category of methods for detecting the islanding condition. All of the methods are listed with alternative names. The theory of operation when connected to the utility grid and after the utility grid is disconnected is given for each. The strengths and weaknesses of each are treated individually, and each is then analyzed using the non-detection zone (NDZ) criteria to show the effectiveness of the method. No ranking is given to any of the methods. Each country, or in some cases each utility, must determine its needs and choose the criteria needed for safe and reliable operation of the utility grid(s). The passive methods described and evaluated are methods such as: Over/under Voltage Over/under Frequency Voltage Phase Jump Detection of Voltage Harmonics Detection of Current Harmonics The active detection methods for islanding that are typically resident in the inverter are also described. The active methods generally contain an active circuit to force voltage, frequency or the measurement of impedance. The methods analyzed are: Impedance Measurement Detection of Impedance at a Specific Frequency Slip-mode Frequency Shift Frequency Bias Sandia Frequency Shift Sandia Voltage Shift Frequency Jump ENS or MSD (A device using multiple methods) The methods not present 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. They are also discussed in detail and included: Impedance Insertion Power Line Carrier Communications Supervisory Control and Data Acquisition This report also describes the rationale for the need for anti-island test methods and test circuits. Several test methods that may be used for determining whether the anti-islanding method is effective are described in detail. Preliminary results of testing using motors instead of RLC circuits indicate islanding tests can be conducted using RLC circuits. Most test circuits and methodologies have been chosen to limit the number of tests by measuring the reaction of a single or small number of inverters under worst-case islanding conditions.

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