A variable frequency drive (VFD) is a motor drive used to control motor speed and torque by adjusting frequency and voltage. It is often used in water pumps, pool filtration systems, compressors and other commercial and industrial applications.
In the past, VFDs had a higher upfront cost when compared to motor soft starters. Because of this, their use in industrial applications was limited. However, over the last few decades, the cost of VFDs has been reduced through the use of the latest power electronics technology.
So, why use VFDs over other motor drive types? Is it the right drive to use for your particular project?
To help you answer those questions, we’ve listed the advantages of using a VFD.
Controlled start-up current
With other motor speed controllers, it can take up to eight times the full-load current just to start the motor. This current generates a lot of heat, which will eventually wear down the mechanisms of your system.
With VFDs, however, the current needed to start the motor is significantly lower. This makes VFDs a much more efficient option than other motor drives. Since a lower starting current is needed, the amount of heat generated in the start-up is much less. This improves the lifespan of the motor, which, in turn, can save the user money in the long run.
Fewer power line disturbances
The starting-current demand of an AC motor can easily drain the power system that is linked to it.
Overloading the system can cause a power sag, which is a short dip in the RMS value of the line voltage. This sag can lead to computers, sensors, switches or any other equipment connected to the system to stop working properly. In some cases, it might even cause significant damage to the electronics and machinery.
With VFDs, however, the motor is started at zero voltage and is gradually ramped up. This means the risk of overload and power sagging is reduced significantly. This can make a particular workflow run more smoothly. More importantly, it can also help users avoid damaging their expensive equipment.
Controlled acceleration and deceleration
Using a full-voltage starter (or an across-the-line starter) can shock the system as it abruptly accelerates the motor. This sudden acceleration can cause wear and tear on the mechanical parts of the motor overtime. It can also damage the products that are involved in the process.
One of the advantages of using VFDs is the ability to control acceleration and deceleration. VFDs start at zero and smoothly ramp up the acceleration. This prevents damage to the motor as well as to the involved products. VFDs can also decelerate the motor at a gradual pace.
Ramped up acceleration and smooth deceleration improves the longevity of your motor.
Adjustable Operating Speed
One of the more significant advantages of using a VFD is the ability to control its operating speed.
Other motor drives, like soft starters, only operate at a set speed. This can be an issue when different motors speeds are needed in a single production process. Also, since some drives only operate at a full speed, it can cause damage to the products and materials that require a slower motor motion.
Through the use of Programmable Logic Controllers (PLCs) or other process controllers, a VFD user can easily adjust the speed of the AC motor as necessary. This will allow them to optimise a process that requires both slow and fast motor speeds. It also allows for more precision. More importantly, it can reduce the risk of product damage as the user can adjust speed, torque and force depending on the application.
In industrial applications, sometimes it’s necessary to keep the motor spinning for a long period of time. In such a situation, moderation of motor speed and energy consumption is key.
Motor drives with constant torque will run the motor at full-speed throughout the whole process. However, not every application requires maximum speed and torque. By running the motor at an unnecessarily fast speed, a lot of energy will be wasted.
On the other hand, VFDs with variable torque are much more energy efficient as it allows the user to reduce the motor speed as necessary. In fact, in some applications, it is beneficial to vary the motor speed at different times. VFDs can reduce energy consumption significantly, which can save users money in the long-term.
Using VFDs has it’s benefits. However, you do need to make sure that it’s application is appropriate. If you’re unsure, don’t hesitate to contact a specialist to help you out with your project.