What is a Variable Frequency Drive?
What is a VFD?
A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, microdrive, and inverter.
Frequency (or hertz) is directly related to the motor’s speed (RPMs). In other words, the faster the frequency, the faster the RPMs go. If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement.
How does a Variable Frequency Drive work?
Incoming AC voltage is converted to DC voltage by the diodes, the sine wave changes from a three phase wave to a single chopped DC wave form. The capacitor section takes the chopped wave form and smooths it out to a controllable DC voltage. This voltage will be the square root of 2 times the incoming voltage, i.e. a 480 volt system will have a 650-700 volt DC voltage. The IGBT’s (Insulated Gain Bipolar Transistor) then convert the DC voltage back to a “Pulse Width Modulated” (PWM) wave form to send to the motor. The PWM wave form simulates the AC waveform in short pulses.
Since the Variable Frequency Drive controls both the frequency (number of time above and below the zero crossing of the sine waves) and the duration of the on/off, we can send the desired voltage and frequency for the most efficient energy usage.
Why should I use a VFD?
Reduce Energy Consumption and Energy Costs
If you have an application that does not need to be run at full speed, then you can cut down energy costs by controlling the motor with a variable frequency drive, which is one of the benefits of Variable Frequency Drives. VFDs allow you to match the speed of the motor-driven equipment to the load requirement. There is no other method of AC electric motor control that allows you to accomplish this.
Electric motor systems are responsible for more than 65% of the power consumption in industry today. Optimizing motor control systems by installing or upgrading to VFDs can reduce energy consumption in your facility by as much as 70%. Additionally, the utilization of VFDs improves product quality, and reduces production costs. Combining energy efficiency tax incentives, and utility rebates, returns on investment for VFD installations can be as little as 6 months.
Increase Production Through Tighter Process Control
By operating your motors at the most efficient speed for your application, fewer mistakes will occur, and thus, production levels will increase, which earns your company higher revenues. On conveyors and belts you eliminate jerks on start-up allowing high through put.
Extend Equipment Life and Reduce Maintenance
Your equipment will last longer and will have less downtime due to maintenance when it’s controlled by VFDs ensuring optimal motor application speed. Because of the VFDs optimal control of the motor’s frequency and voltage, the VFD will offer better protection for your motor from issues such as electro thermal overloads, phase protection, under voltage, overvoltage, etc.. When you start a load with a VFD you will not subject the motor or driven load to the “instant shock” of across the line starting, but can start smoothly, thereby eliminating belt, gear and bearing wear. It also is an excellent way to reduce and/or eliminate water hammer since we can have smooth acceleration and deceleration cycles.