What is a VFD?

Select ElectricalGeneral

Photo of open Variable Frequency Drive (VFD) Panel

If you are a newcomer to the world of electric motors, you may hear the term “VFD” thrown around a lot. What a VFD stands for Variable Frequency Drive, which can also be referred to as an AC Drive, or an Inverter. That is all well and good, but what actually is a VFD, how does it work, and why is it used?

What is a VFD?

A Variable Frequency Drive (VFD) is a sophisticated motor control system. A VFD controls the speed of an electric motor by varying the voltage and frequency that is supplied to the motor. Variable Frequency Drives were first made available in the late 1950’s and have increased in efficiency and effectiveness with strides in electronics over time.

A VFD system can replace common mechanical controls in systems such as valves on pumps or louvers for fans. When in operation a VFD will only send the necessary power to the motor to meet the real-time requirements of the system. The VFD will adjust the motor output to match changes in the requirements of the system. The drives can be used as phase converters, converting single phase input into three phase inverter output.

A VFD is comprised of three main components: A Rectifier, a DC link, and an Inverter.

Variable Frequency Drive VFD CFW11 Schematic

The rectifier converts the AC supply into DC power. The DC Link supports voltage through the drive from the rectifier and inverter, the DC link stores power converted by the rectifier. Capacitors in the DC link absorb the remaining AC ripple and delivers smooth DC voltage. This DC voltage is converted into an AC voltage by switching transistors in the inverter and sent to the motor. The Variable Frequency Drive varies the output frequency by switching transistors connected to either the positive or negative DC bus. The drive can change the voltage output by pulsing the DC voltage appropriately over the required frequency, this is called Pulse Width Modulation (PWM). If the voltage is ON half the time the average voltage will be 50%.

Variable Frequency Drive VFD PWM Output

The WEG CFW11 drive is controlled via an on-board programmable logic controller (PLC). The customizable software in the plc allows the CFW11 to control a large number of systems.

Benefits of Variable Frequency Drives

Power Savings

A good incentive to upgrade motor control to a VFD is power savings. In all systems replacing mechanical motor throttling with a variable frequency drive will result in power savings. Systems run by pumps and fans are common systems where replacing existing mechanical throttling will provide significant power savings.

Performance Control

Using a VFD will decrease electrical and mechanical stress in the system during acceleration and deceleration by smoothing the rise or drop in motor RPM. Reducing stress in the equipment will increase the lifespan of components and decrease unscheduled downtime.

Increased Quality Control

By controlling your motors at the most efficient speed for your application, fewer mistakes will occur, and overall production levels will increase - effectively earning your company higher revenues and saving on scrap. Additionally, a VFD helps eliminate jerks on conveyors and belts start-up allowing high through put.

Interested in a Variable Frequency Drive?

Select Electrical Enterprises Ltd. has the right WEG VFD for your motor, in both low voltage and high voltage. If you are unsure on what VFD is right for you, we encourage you to contact us via phone (780-968-8859) or fill out our online contact form. Find the right VFD for your application today.