Adding a drive to meet energy regulation

Part of a European motor efficiency standard allows use of a variable speed drive to meet energy-saving requirements.


Interior permanent magnet (IPM) motors are one of many solutions to motor efficiencies above premium levels. In a cooling tower fan application, this direct-drive IPM motor (and adjustable-speed drive) eliminated a worm-gear reducer used with a two-speedPhases 2 and 3 of European Union regulation EC No. 640/2009 mandate use of IE3 class motors starting in 2015 and 2017—depending on motor size range (see main article, "Motor-Driven Systems Efficiency Update," linked at the bottom). However, the regulation includes a notable option. In lieu of an IE3 motor, it allows the following “or” option: “…or meet IE2 efficiency and be equipped with a variable speed drive [VSD].” As far as it’s known, this is the only efficiency standard to date where a VSD is formally included.

There is good reason for this provision. VSDs (also called variable frequency drives, VFDs) can match motor output to changing load conditions in variable-torque applications, thereby cutting energy losses. Indeed, the EU is counting on the huge number of such pump, fan, and compressor applications—reportedly 2/3 of all applications—to deliver meaningful efficiency gains through use of a drive. Of course, an IE3 motor and VSD combination would be even more efficient, but marketing issues have held off earlier European adoption of the higher IE-class motor.

Meanwhile, VSDs and motor-drive combinations are drawing attention from the efficiency viewpoint. While VSDs are quite efficient at nominal speed/torque, with losses typically amounting to 2%-5%, at 25% speed/torque VSD losses can reach 10%-30%, according to Ref. 2. These factors must be assessed or improved, if possible, when implementing drive systems.

One development in this area is Canadian Standards Association (CSA) draft standard C838, Energy Efficiency Test Methods for Three-Phase Variable Frequency Drive Systems. Covering drive and motor combination “systems,” CSA C838 establishes appropriate testing requirements and procedures that compare efficiency at different system speed and load points. The basis of this draft standard derives from the work of Pierre Angers, an engineer with Hydro-Quebec of Canada, and it has been cited earlier in Control Engineering (Ref. 9). CSA C838 is a work in progress, with the comments period having closed on April 8, 2012.

See the main article, “Motor-Driven Systems Efficiency Update,” for further motor system efficiency developments, linked at the bottom of this article.

- Frank J. Bartos, PE, is a Control Engineering contributing content specialist. Reach him at 

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