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Connecting Variable Frequency Drive (VFD) to a 3 Phase Motor

Mike Jeffries | January 11, 2021

Screen Shot 2017-01-10 at 4.41.37 PM.pngVariable frequency drives (VFDs) are one of the most efficient methods of controlling motors that are designed to operate at a single speed. Depending on the VFD and how it is installed, a VFD operates on single or 3 phase input, and the output matches the desired voltage. Because the motors are typically designed with a single operating speed, the VFD is required to alter the speed of the motor.

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Related Blog: Can You Use a Variable Frequency Drive (VFD) on a Single Phase Motor?

Understanding a Variable Frequency Drive

There is a layer of control between the input and output functions of a VFD. The control panel acts as an interface that converts AC input to DC current and then simulates AC output using a conversion process known as Power Width Modulation, or PWM. Since the output is conditioned by the VFD, the input power does not have to match the desired output.

VFDs and Single Phase Input

It is not necessary to have 3 phase electrical input in order to operate a 3 phase motor with a VFD. The electronics of the VFD will step up single phase current during the conversion process. To do this, input power is first converted to DC current using diodes, and then converted to the desired output current using capacitors and diodes which create pulsed power simulating AC current. A 3 phase motor simply attaches to the appropriate output connectors on the VFD. Corresponding input voltage is not a factor in the output voltage.

VFDs and 3 Phase Input

When 3 phase input is used, the wiring must be processed through an inverter to yield DC current. The wiring is similar to a single phase input, with the exception of multiple leads being inverted. The mechanical operation of the VFD remains the same, and output is controlled by the VFD. To avoid complications and reduce errors, enlist the assistance of a professional professional motor and Controls Company during the installation process.

Regardless of the voltage input required by the motor, professional installation is required. At Mader Electric, we have
more than 30 years of experience with high output motors, pumps, and conveyors in the Southwest Florida region. Our trained technicians are available to install or troubleshoot your systems using motors up to 4000 horsepower in size.

Related Blog: Variable Frequency Drive (VFD) Frequently Asked Questions

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