Harmonic Mitigation Strategies in Variable Frequency Drive Applications.

The demand for higher efficiency HVAC systems has led to fast adoption of energy saving modern variable frequency drives (VFDs) and motor control technology. The successful introduction of VFD controlled compressors, pumps and fans into chillers and air handlers has helped meet these demands and led to rapid deployment into data centers, hospitals, power plants and other critical cooling markets. Some benefits of variable frequency technology include i) smaller air handing packages using high-speed electrical motors and ii) higher partial load system energy efficiency, where the complete system is considered from electrical input to HVAC load. However, they also produce harmonic electric currents that lead to poor electrical power quality and equipment failure if levels are not kept low enough. Harmonics and power quality have never been more important to understand and mitigate as the adoption levels of VFD controlled HVAC equipment increase along with increasing harmonic levels. The goal of this technology review paper is to: • Explore the causes and effects of harmonics in common types of variable frequency drives used in chillers and air handlers - the standard 6-pulse diode front end drive. • Compare today's most effective harmonic mitigation technologies, which include passive harmonic filters, active harmonic filters, and active front end drives. There are multiple harmonic current mitigation strategies and technologies available to VFD users. Every manufacturer of harmonic filters, standard 6-pulse diode rectified VFDs and active front end drives provide data to support their technology as a superior solution. Each technology can generally meet the most stringent harmonic requirements in IEEE Std 519-2014 Recommended Practice and Requirements for Harmonic Control in Electric Power Systems. The problem is that these solutions are often narrowly focused to coincide with inherent differences in the technologies. This paper will focus on the economics of a variety of variable frequency drive applications and associated current harmonic mitigation strategies with the goal of showing that the correct solution depends more on matching solution to application than simply superior technology. [ABSTRACT FROM AUTHOR]