Variable Frequency Drives have many and varied uses over a range of applications in industry. In irrigation, a VFD is an electronic device controlled from an electric panel and attached to the irrigation pump motor. It's used to vary the frequency and voltage supplied to the pump motor. Frequency (or hertz) is related to the speed (RPM) of a motor; the higher the frequency, the higher the RPM. The VFD effectively varies the speed of the pump motor according to need. For this reason it's considered a useful tool in pumping efficiency.