January 2005 • NREL/TP-560-37200 Grid-Connected Inverter Anti-Islanding Test Results for General Electric Inverter-Based Interconnection Technology Z. Ye and M. Dame General Electric Global Research B. Kroposki National Renewable Energy Laboratory National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle Contract No. DE-AC36-99-GO10337 January 2005 • NREL/TP-560-37200 Grid-Connected Inverter Anti-Islanding Test Results for General Electric Inverter-Based Interconnection Technology Z. Ye and M. Dame General Electric Global Research B. Kroposki National Renewable Energy Laboratory Prepared under Task No. DP05.1001 National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle Contract No. DE-AC36-99-GO10337 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. 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Box 62 Oak Ridge, TN 37831-0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:[email protected] Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: [email protected] online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste Executive Summary One concern about the installation and operation of distributed generation on the electric power system is islanding. Islanding is defined in Institute of Electrical and Electronics Engineers (IEEE) Standard 1547 as: a condition in which a portion of an Area Electric Power System (EPS) is energized solely by one or more Local EPSs through the associated point of common coupling (PCC) while that portion of the Area EPS is electrically separated from the rest of the Area EPS. [E1] Typically, distributed generation manufacturers incorporate anti-islanding functionality into their equipment to ensure it detects electrical islands and disconnects from the electric power system properly. This report summarizes the anti-islanding testing results of an inverter-based interface for distributed generation. The testing was conducted at the General Electric (GE) Research Laboratory and the National Renewable Energy Laboratory Distributed Energy Resources Test Facility. The objectives of the testing were to: • Perform experimental validation of the effectiveness (determined by the time needed to detect and isolate distributed resource equipment from the grid) of proposed GE anti-islanding schemes • Perform parametric evaluation of the GE anti-islanding schemes with respect to control settings and load conditions, including controller gains, load power levels, and load quality factors • Develop recommendations for the IEEE P1547.1 working group • Explore low-voltage ride-through characteristics. Findings of the testing included: • Using a matched load, the inverter can be islanded (more than 2 seconds) without any anti-islanding measures activated. In some cases, depending on load match and quality factor, the inverter can run on indefinitely. • With the recommended anti-islanding parameter settings, the schemes work successfully (trip within 2 seconds) under all tested conditions, including worst-case generation/load balance as defined in the IEEE P1547.1 testing standard [E2]. • The anti-islanding testing results were repeatable under fixed conditions and parameter settings. iii • The predicted effectiveness of the voltage and combined schemes did not correlate with load level. It was predicted the schemes would react more quickly at low loading conditions. However, this was not always observed in testing. More testing is needed to draw conclusions from the observations. • When both voltage and frequency anti-islanding schemes were enabled, tripping time was not faster. This indicates there is some interaction between the schemes. It is recommended that only one scheme be used so performance is more predictable. More study and tests are needed for a better understanding of interactions in combined schemes. • When a positive feedback control is employed, there is a critical gain below which the positive feedback control will fail to detect unintentional islanding and result in certain non-detection zone. • Given the configuration of an unregulated DC bus obtained from a diode rectifier, the inverter is not able to ride through a low-voltage event on the utility grid, regardless of whether anti-islanding is enabled. To have low-voltage ride-through capability, the DC bus voltage must be regulated so that the inverter can be operated as a constant current source. Because of issues found during this testing, it is recommended the testing be repeated over a larger range of conditions. iv Table of Contents List of Figures ............................................................................................................................................ vi List of Tables............................................................................................................................................. vii 1 Introduction ........................................................................................................................................ 1 1.1 Objectives...................................................................................................................... 1 1.2 Inverter Description...................................................................................................... 1 1.3 Test System Description ............................................................................................... 2 1.4 Anti-Islanding Schemes ................................................................................................ 3 2 Testing Results................................................................................................................................... 5 2.1 Test Procedure............................................................................................................... 5 2.2 Test Results................................................................................................................... 6 2.2.1 Voltage Scheme ............................................................................................. 7 2.2.2 Frequency Scheme ......................................................................................... 8 2.2.3 Combined Voltage and Frequency Scheme ................................................... 9 2.2.4 Gain Variation Effect ..................................................................................... 9 2.2.5 Low-Voltage Ride-Through Test................................................................. 10 3 Summary ........................................................................................................................................... 12 3.1 Findings....................................................................................................................... 12 3.2 Recommendations....................................................................................................... 12 4 References ........................................................................................................................................ 14 v List of Figures Figure 1. GE grid-connected inverter product platform.......................................................... 2 Figure 2. The inverter test package ......................................................................................... 3 Figure 3. Unintentional islanding test protocol ....................................................................... 5 Figure 4. NREL laboratory test results without anti-islanding control ................................... 6 Figure 5. GE laboratory test results without anti-islanding control ........................................ 7 Figure 6. NREL laboratory test results with voltage anti-islanding scheme........................... 8 Figure 7. GE laboratory test results with frequency anti-islanding scheme............................ 9 Figure 8. Test results with abnormal utility condition........................................................... 11 vi List of