How do you best manage the harmonics created by variable frequency drives? An interview with two subject matter experts with a focus on critical buildings.
Variable frequency drives (VFDs) are increasingly integrated in industrial IoT certification and critical power environments. Research indicates that the VFD market is growing due to ongoing industrialization and urbanization while drives get ‘smarter’.
Most, if not all harmonic compliance requirements in the world, such as IEEE 519, call for less than 5% total harmonic distortion
Electrical devices with non-linear loads, including anything with a switch-mode power supply i.e. personal computers, LED lighting, AC and DC motor drives, will all generate some degree of harmonics.
The application of VFDs also produces harmonic current from the output of the inverter. These harmonics can be harmful to the motor itself, and unless properly mitigated, will resonate across the larger electrical power system. Since there are many industries and applications in which various VFDs are used, the solutions to deal with harmonics differ.
In this interview with Jean-Pascal Riss and Nicolas Larue from Schneider Electric we look at VFDs, harmonics and why/how to mitigate harmonics caused by VFDs with a focus on critical power facilities.
Selecting the right approach for the right application is crucial for several reasons as our experts will explain. Jean-Pascal works in Schneider’s Industrial Automation division, while Nicolas works in Schneider’s Energy Management division; and conveniently enough the convergence of energy management and industrial automation is at the root of this application challenge. We’ll start our discussion with an overview of VFDs, harmonics, harmonic mitigation approaches and the reasons why it all matters.
Setting the scene: the role and energy saving benefits of variable speed drives
Jean-Pascal, you are the Offer Category Director for the Low Voltage Variable Speed Drive (VSD) end user market at Schneider Electric. Can you explain us the role of VFDs or VSDs?
Jean-Pascal Riss: Variable speed drives are the electronic devices that today control almost all electrical motors in industrial processes with moving components, including fluids such as water or air. To control such processes, at one point you need to be able to control the speed of the involved motors.
In the past there were many technologies to do so but since give or take fifteen years we only use variable speed drives. The adoption of VSDs has been exponential. The technology is based upon the IGBT (insulated-gate bipolar transistor), a silicon device that provides different frequencies to the motor. It was first developed and used in Japan. Gradually quality improved, costs went down, and now variable speed drives are omnipresent.
Where is the demand to use them coming from?
Jean-Pascal Riss: Well, the main purpose of drives is to provide a precise regulation of electrical motors which enables energy savings. Since drives consume over 70% of the electrical energy, depending on the environment: in industrial processes it’s over 80% and in buildings more than 40%. This means precise control on the energy usage of a drive means huge energy cost savings, and a greener approach to operations. A typical example in buildings are HVAC systems (Heating, ventilation, and air conditioning) which you want to provide with just enough energy to have precisely enough cooling capacity, but not so much that you are running your motors at full speed anytime the system is turned on.
VFDs and harmonics: the challenge and the mitigation approaches
Ok, so the opportunity is clear, but what’s the downside, or implication of this pervasive use of VFDs? Nicolas Larue, with the system level approaches Jean-Pascal mentions we’re more on your domain since you are globally responsible for the AccuSine range of active power correction filters at Schneider Electric. Can you tell us more about harmonics, harmonic mitigation and this system level approach whereby such an active power correction filter is used?
Nicolas Larue: Sure, energy savings are great, but the implication of using equipment like VFDs is the generation of harmonic current which could impact electrical reliability.
Simply put a harmonic current is a frequency that is different from the fundamental frequency in an electrical network, which, depending on the country, is either 50Hz or 60Hz. When you add a device such as a VFD to an electrical network the perfect sign wave of this fundamental frequency gets distorted, and the more you use, the more this is distorted. This is often represented with THD or Total Harmonic Distortion or explained through Power Factor.
Harmonic mitigation enables us to reduce the distortions caused by changing the frequencies and…