What Are Variable Frequency Drives?

What is a variable frequency drive, and how does it work? A variable frequency drive (VFD) is a piece of technology in Upland, CA that’s housed inside an electric motor. It drives that motor by sending variable frequencies and voltages of its power supply, and is capable of controlling both the ramping up and down of the motor during periods of starting or stopping.

While the VFD technically controls voltage and frequency, this is a process often referred to as speed control, because the result of those voltage and frequency changes is changes in speed of the motor.

Here are just a few examples of some of the benefits of adjusting motor speed using a VFD:

  • Improved efficiency and energy savings
  • Ability to match the drive speed to the requirements of your process
  • Ability to match the torque or power of the drive to the requirements
  • Ability to convert power in hybridization settings
  • Lower levels of mechanical stress on machines, allowing them to have extended lifespans
  • Improved working environment
  • Lower levels of noise during operation, particularly from pumps and fans


Perhaps the biggest advantage that comes with using a variable frequency drive is the ability to optimize your energy consumption and improve overall efficiency. These drives are capable of drastically cutting down on energy consumption, especially as compared to direct-on-line (DOL) operation, in which the motor operates at full speed at all times, regardless of the demands and needs of the application.

With a VFD, you can achieve fuel or power savings of up to 40 percent or more. The roll-on effect ensures using the VFD also cuts down on nitrous oxide emissions and the overall carbon footprint of the systems in which the drive is installed and used.


There are multiple varieties of these drives available, which makes sense considering their broad range of uses within industrial settings. There are both single- and three-phase VFDs, which can be used to suit a wide range of applications. The differences in drive types include the methods used for controlling frequency and voltage, as well as harmonic mitigation.

Of the most common frequency designs used in these drives, three of note include current source inverter, voltage source inverter and pulse-width modification (PWM), the latter being the most common. PWM involves switching the AC drive’s inverter power sources—which can either be insulated-gate bipolar transistors or standard transistors—on and off over and over again to generate the proper voltage levels. The PWM controls and varies the width of those pulses, which results in varied output voltage and frequency.

Interested in learning more about the various types of VFDs available on the market and what their benefits can do for your operation? We encourage you to contact Ham’s Electric, Inc. for more information on what a variable frequency drive is and how it works, as well as any of the numerous services we provide to our clients in Upland, CA. Our experts will be happy to speak with you and answer any questions you have for us.