During this period, vfd's have evolved from using analog-based electronics with limited flexibility and control capability to on-board microprocessors with advanced control and communications capability. Advances in power switching devices and power control algorithms have provided higher efficiency, improved accuracy, reduced noise levels, and bidirectional power flow capability. These benefits however, come at the price of a more sophisticated and complex device, requiring more knowledge for its effective application.
The basic principles of operation and energy benefits of vfd's are well understood by most hvacr designers and have been previously discussed at length in this (see "Basics of Vsd's" by Mark Ziemer, P.E. in the August 1999 issue of ES) and other publications. This article will instead focus on some of the application issues that are critical to successful integration of vfd's into the hvacr control system and the building electrical system.