When we see a person yelling for what we believe is 'no good reason,' sometimes it wears us out! We think: "Good grief! Why on earth is that person going so over-the-top about something so trivial?" As Video #1 below depicts, that is the basic concept behind drive technology. Stop telling your motor, which is likely over-sized for the job it is doing, to scream at the problem. Control it so that its volume matches the conversation, i.e. its work matches the system requirement, and save money in the process.
Video #1: A metaphor for variable frequency drives
Now that we understand the basics, we might be more comfortable describing variable frequency drives (VFDs) by their other name, variable speed drives. Based on Video #1, this makes sense, right? The drive is varying the speed of the motor, but to have a better understanding of the technology, we have to investigate the engineering behind the solution. Video #2 gives an overview of the history of motors, the physics of their operation, and the role that drives play in motor function.
Video #2: A lovely British gentleman teaches us the basics of motors and drives
Video #2 explains that the major obstacles motors had to overcome to supplant their predecessors (horses and steam) were: 1) The ability to start smoothly. 2) Excellent speed control over their operating range. In AC induction motors, the best way to address these two requirements is to control the frequency of the current supplied to the motor. Video #3 discusses a VFD's use of just four elements, a rectifier, a DC link, a converter, and a control circuit, to achieve frequency control.
Video #3: A fantastic explanation of drive fundamentals, function, and application
In terms of energy technology buckets, variable frequency drives fall into energy efficiency, and this post will be tagged as such, but VFDs are part of nearly every energy investment that might interact with a motor. Want to enroll in demand response? You'll need VFDs to protect your motors from sudden stops and starts. Want to install solar panels on your rooftop? You'll likely need regenerative drives to feed power back onto the grid. And, the most natural association of all, want to upgrade the efficiency of your heating and air system, which accounts for approximately 32% of the energy budget your commercial building? Drives will be your first investment. Did I mention that the average drive payback period is 2 years or less and that nearly every utility offers energy efficiency incentives for their installation? We'll leave that discussion for another post.
