Electronic Design

A Convocation Of Standards

The breakthrough standard for PV inverters was IEEE 929-2000, Recommended Practice for Utility Interface of Photovoltaic (PV) Systems. But when it came time to reconcile the design standard with practices in the utility industry, two other standards were created: IEEE 1547, Standard for Interconnecting Distributed Resources with Electric Power Systems; and UL1741, Standard for Inverters, Converters and Controllers for Use in Independent Power Systems.

The IEEE Standards Board approved IEEE 1547 in June 2003, and it was approved as an American National Standard in October 2003. UL1741 is the standard the utilities care about, though. But for actual inverter performance requirements, it references IEEE 1547.

So how does IEEE 1547 differ from IEEE 929? The key difference is noted in the title. It refers to "distributed resources," not just "PV systems." Distributed resources cover inverters for everything used to generate non-utility power that could connect to the grid: PV modules, windmills, fuel cells, and even flywheels.

Not that this makes a difference in terms of inverter-performance requirements-they're identical in both documents. However, IEEE 929 contains a great deal more information about how photovoltaic inverters work. On the whole, IEEE 929 is a much more useful document for Electronic Design readers who might want to get into the solar inverter business.

John Stevens, a principal member of the technical staff at Sandia National Laboratories and a major player in the development of all three standards, explains that IEEE 1547 was deliberately limited to the bare bones of performance specs and testing methods to accelerate the implementation of UL1741.

Other important documents include NEC (National Electrical Code) Article 690, Solar Photovoltaic Systems, which is of importance to PV installers and building officials, and UL Standard 1703, Flat-plate Photovoltaic Modules and Panels, which is the safety standard for PV modules. The latter tells the building inspector and customer that a solar generating unit is safe when installed according to the manufacturer's directions.

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