Grid Scale, Microgrids, Solar, Utility Integration

AEIS on PV islanding and grid-tie considerations

After a demonstration of Solar Energy Grid Integration System technology by Advanced Energy Industries Inc. (Nasdaq:AEIS), the company’s control solutions manager for advanced energy, Michael Mills-Price, spoke with senior technical editor Debra Vogler about the solar photovoltaics inverter control project, and what “islanding” means for a solar installation.

September 26, 2011 — Advanced Energy Industries Inc. (Nasdaq:AEIS) demonstrated Solar Energy Grid Integration System (SEGIS) technology at an event this month in Portland, OR. The SEGIS program is funded by the U.S. Department of Energy (DOE) Solar Energy Technologies Program (SETP), and aims to develop technologies that make solar power cost-competitive with traditional power generation sources. The event featured technologies the company developed as a result of its being awarded a Stage 3 SEGIS contract by the U.S. DOE in September 2010.

The company partnered with Schweitzer Laboratories, Portland General Electric, Northern Plains Power Technologies, and Sandia National Laboratories to develop solutions to key challenges facing high PV penetration into today’s electrical grid. The demo featured a live demonstration of synchrophasor-based islanding detection as well as advanced inverter control functionality, which the team has integrated into grid-tied solar inverters to enable performance improvements both at the PV site as well as at the distribution feeder level.

Michael Mills-Price, Control Solutions Manager, Advanced Energy, told ElectroIQ.com that one of the technologies being launched is the application of two-way communication and synchrophasor measurements built into grid-tied solar inverters to enable better control over PV systems. This technology is used for island detection. Islanding occurs when a section of the power system including generation and load becomes electrically isolated from the main grid and enters a standalone or micro-grid mode of operation, said Mills-Price. When islanding occurs outside the control of the utility, he explained that it?s undesirable because it?s unsafe and causes damage to the distributed generation equipment. Listen to the podcast with Mills-Price below.



Applicable standards, such as IEEE 1547, require that distributed generators include a means to prevent unintentional islanding. Methods used by the power industry to detect island formation are passive (relying on changes in distributed generation terminal measurements), active methods (the distributed generator perturbs its current waveform looking for something to happen with the voltage waveform), and communications-based methods (system status info is communicated to the distributed generator device). The passive methods are subject to false trips. The active methods have a number of difficulties: they may fail under certain field conditions (with multiple site installs), they tend to conflict with grid support functionalites, and they tend to degrade power quality; some active methods will fail to detect an island in specific cases. The communications-based method overcomes the failings of the active and passive methods and works in a high-penetration environment.

The communications-based method relies on a statistical relationship between a frequency measurement by a local phasor measurement unit and a reference phasor measurement located upstream. When an island forms, clear differences are seen in the statistical relationship between the local frequency measurements and the reference unit; upon detection of the island, the inverter can be tripped offline. Mills-Price provides a detailed assessment and description of these various methods in the podcast.

Also check out this graphic illustration of islanding and the distributed power grid below.

Advanced Energy (Nasdaq:AEIS) makes innovative power and control technologies for high-growth, thin-film manufacturing and solar-power generation. For more information, go to www.advanced-energy.com.

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