AC Variable Frequency Drives (VFD)

What is a Variable Frequency Drive?
Variable Frequency Drives, also referred to as AC Drives, AC inverters, Variable Voltage Drives, or Variable Speed Drives (VSD), are solid-state devices that are used to control the speed of 3-phase AC motors. Their most common application is the control of 3-phase AC induction motors. An AC induction motor’s speed is dependent upon the motor’s physical construction. Specifically, the number of electromagnetic poles distributed in the motor’s stator and the frequency of the AC voltage applied to the motor determine its speed.

A VFD provides a variable frequency voltage waveform to an AC induction motor. Since the motor’s speed is dependent on the frequency of its AC voltage, the drive provides control over motor speed by changing both the voltage and the frequency of the motor’s AC waveform.

Where are VFD Drives Used?
VFDs are used with a large variety of machines due to their ability to reduce system stress on and increase control of motors that otherwise have a fixed speed.

Examples include:

• Extruders
• Conveyor Belts
• Roller Tables
• Fans / Exhausters
• Centrifugal Pumps
• Granulators / Palletizers
• Dryers and Rotary Ovens
• Process Dosing Pumps
• Stirrers / Mixers
• Rotary Filters
• Winding Machines / Uncoiling Machines

Who Uses AC Drives?
VFDs are used in many industries such as:

• Industrial Control
• Material Handling
• Oil and Gas
• Food and Beverage
• Mining
• Power Generation
• Heating and Air
• Cement

Selecting a Variable Frequency Drive
It is imperative to know some information about your motor to select the proper AC Drive application. Here are some important factors to determine before making your selection:

What Environment Will Your Drive Be Installed In?
Ideally, AC Drives will operate in a cooled and clean environment. Failing to keep the AC Drive properly cooled, cleaned, and ventilated can result in failure of the device. We offer three main chassis types with different environmental ratings:

• IP20 – Indoor finger-safe protection against solids over 12.5mm, or about half an inch. No protection against liquids.
• NEMA 1 – Indoor use primarily to provide protection against contact with the enclosed equipment and against a limited amount of falling dirt.
• NEMA 4 – Protection against dust, dirt, and similar small debris and a degree of protection against liquids. Able to be installed outdoors when protected from direct sunlight.

On all AC Drive chassis types, it is critical that the heat sink and fans are kept clean.

Other Considerations
There may be other factors to consider depending on your application when sizing your AC Drive.

• Does your application require derating of the AC Drive?
• Is your application outside of normal use for the AC Drive?

De-rating
AC Drives may require de-rating to accommodate for:

• Using a 3-phase input drive with single phase input
• Rapid acceleration/deceleration
• Excessive rate of starts and stops
• High altitudes
• Ambient temperatures (including temperature inside enclosure) exceeding 40°C
• Loads that require higher-than-normal starting torques

[Click here for an example on how to de-rate three phase input AC Drives for single phase input using the FMX TD400]

Special Considerations
Some applications operate beyond the normal considerations of AC Motor and/or AC Drive design. These applications can include (but are not limited to) applications with excessive start/stop cycles and fast cycle times, higher than normal starting torque, overhauling, highly regenerative loads, DC motor replacement applications, solar applications, and irregular voltage and/or speed patterns. If your application features these or other special considerations, please contact our technical support staff to ensure that you are choosing the right AC Drive for the job.

FMX
When you see the FMX brand on a product it means you can be assured of high quality and competitive pricing. Most FMX products are produced in the same factories and on the same production lines as many well-known major name brands offered in the market today. All of these products meet or exceed the expected quality and certification requirements in the United States for many industrial applications and undergo stringent testing to ensure they will perform according to standards in the field.

FMX Products Include:

• Variable Speed Drives
• Miniature Circuit Breakers
• Motor Controls
• Panel Meters
• Relays
• Sensors
• Signal Lights
• Terminal Blocks
• Wiring Solutions

More about FMX

TECO
Since their inception in 1956, TECO Electric & Machinery Co., Ltd. has evolved into a major manufacturer with products spanning many industries including the industrial control industry. TECO produces drives compliant with various kinds of stress, position, speed, turning moment, and load for all-round applications.

TECO Products Include:

• Variable Speed Drives
• Braking Options

More about TECO

WEG
WEG is one of the largest industrial electric control manufacturers, producing more than 21 million units annually and always striving to improve. Attention to detail is the hallmark characteristic at WEG. All products, including their line of AC Drives, are driven by the desire to increase efficiency. WEG manufactures reliable AC Drives with varying module attachments. Depending on the project environment and application, WEG provides a wide variety of product types, sizes, and technology.

WEG Products Include:

• Variable Speed Drives
• AC Motors
• Pushbuttons
• Soft Starters

More about WEG