What is a Variable Frequency Drive (and how does it work?)

A variable frequency drive (VFD), also known as an inverter, is a device that is used to control the speed, direction, and torque of an electric motor. In short, it does this by varying the frequency and voltage that is being supplied to the motor at any given time. 

Essentially, the goal is to ensure that the motor is able to run at a variety of speeds, rather than just maximum.

But, what do you need to know before you purchase one? A lot. It’s important to understand how they work, how they’re going to benefit you, and how to choose the right one to avoid wasting your money on something that won’t work for you.

How Do They Work?

A variable frequency drive works by controlling the speed, torque, and direction of an electric motor in order to improve performance and energy efficiency. 

In terms of speed, the VFD controls this by allowing for smooth acceleration and deceleration, ensuring that there are no harsh changes, and it can be done gradually. 

When looking at torque, a VFD allows for better control at low and high speeds, keeping better control of the unit overall.

As well as this, it’s able to provide a softer stop/start than traditional motors currently have, avoiding harsh stops which can cause mechanical issues over time.

Key Components

Now we know that a VFD is, and how it works, but what are the key components that allow this to happen? 

First, there is the rectifier, or the converter. This takes single phase, or three phase (depending on the drive you choose) incoming AC power, and converts it into DC power.

Second, there is the DC Bus, or the filter. A DC bus has capacitors that work to filter and smooth the DC power that has been created. It then stores the smoother energy and will provide stable DC power to the inverter.

Last, we have the inverter. This converts the DC energy back into AC energy at variable frequency and voltage. It does this using high-speed switching transistors to complete the conversion.

These are the main components and a breakdown of how they work, leading to the end result of controlling the elements of the motor. Collectively, they are known as the power stage components, but there are a few other components to be aware of when it comes to a VFD, these are as follows:

• The control unit, also known as the processor – the brain of the VFD
• Inputs and outputs
• User interface to allow parameters to be set and better control of the motor
• Electromagnetic Interference (EMI) filters to reduce EMI that is generated
• Cooling system to prevent overheating
• Protection circuitry to safeguard against common faults 

What Problem Does A Variable Frequency Drive Solve?

A VFD can actually solve a range of different problems, depending on what you need it for. It offers solutions for general purposes, as well as energy savings, and high-performance drive applications. Currently, many motors are not able to operate at lower speeds, meaning that they are constantly going somewhere near full power, and using more power than necessary. This is disastrous for your energy bill and it simply doesn’t need to be. With the help of a VFD, you can work with lower speed operation, significantly reducing the power consumption of the electric motor, providing a more energy-efficient solution. 

Where Are They Commonly Used?

VFDs are used across a range of industries as they are so useful. Some of their most common uses are as follows:

• HVAC
• Industrial motors
• Pumps
• Conveyors
• Fans
• Wind turbines

They are able to control pretty much everything from small production equipment for businesses, all the way to large pumps. Of course, you will need to look into which VFD you need, single phase or three phase, and ensure that you’re purchasing from a reputable company. 

Advantages Of Using A Variable Frequency Drive

Improved Process Control

One of the main advantages of using a VFD is that it provides improved process control. By assisting the motor in working at a precise speed, and controlling the torque, smoother operation takes place. You don’t have to worry about constant issues such as jarring stops and starts, which could lead to issues with your equipment sooner rather than later.

Energy Savings

Of course, one of the main reasons that people choose to use VFDs is the energy savings. Instead of running at full speed constantly and massively over-consuming power, a VFD ensures that the motor speed is matched to the demand load. As such, the consumption of energy is decreased, and you will see pretty significant energy savings in no time.

Increased Longevity Of Equipment

A smoother process ensures that your equipment will last longer, experiencing fewer issues and therefore needing less maintenance. For example, the lack of jarring stops and starts reduces the shock to elements such as gears, belts, shafts, and more. 

As well as this, controlling the speed, as well as the rate that the motor accelerates and decelerates reduces the risk of overheating or vibrations that can cause damage over time.

Automation And Flexibility

When installed correctly, they are easily integrated with control systems and sensors. They can then be controlled remotely, making life that little bit easier.

Disadvantages Of Using A Variable Frequency Drive

A Higher Cost

Purchasing a variable frequency drive is not cheap. While there are some budget options out there, and companies like RJW Motors offer options to fit those looking for a budget-friendly solution, it can still be quite the hit to your bank balance. Overall, they are more expensive than simple motor starters.

Complex To Set Up

If you don’t know what you’re doing, you’re going to have to spend more money to get someone who does to set this up for you. It’s imperative that the VFD is installed, tuned, and has been through troubleshooting for the best performance. Without this, you could end up with equipment damage or poor overall performance.

Can Be Sensitive To Various Environments

Some VFDs can be sensitive to various environments, meaning that you may need to make adjustments to ensure that they work as they should. Heat, moisture, and dust can all cause issues that you just don’t want to be dealing with, and as such you may need to look into taking measures to prevent problems in harsher environments.

How To Choose The Right Variable Frequency Drive

Choosing the right VFD is essential to success, and seeing the results that you require. One of the most crucial elements of choosing the right VFD is to ensure that you are matching it to the ratings of your motor. You will be able to find this information on the nameplate of your motor, allowing you to determine which VFD will work in harmony with yours. As well as this, you must consider the power supply.

It’s also handy to know that inverters can also be used to supply 3 phase motors from a 1ph supply, up to 4kw single-phase input and produce a three-phase output, enabling the use of three-phase motors where only single-phase power is available. Larger drives almost universally require a three-phase input, and RJW Motors offers both a budget and premium option for the three-phase inverter.

You’re also going to need to consider the environment in which your motor is. As we mentioned above, the environment can impact the overall performance of the drive, which means that you need to carefully consider how well the drive is going to operate in the conditions you need it to. 

Of course, if you ever need help choosing the right VFD, there are experts on hand to talk you through your options, and ensure you make the right choice.

So, What Do You Need Overall For Success?

To sum it all up, you need to do three things if you have any hope of your VFD providing you with the best possible results:

1. You need to ensure that you choose the right drive for your specific application and environment 
2. You need to ensure that it is installed correctly, following the best safety practices and standards
3. Maintain it well with regular checks and smart monitoring technology 

We hope that you have found this article insightful, and now have a stronger understanding of what a variable frequency drive is, and how it works, as well as a range of other information that is useful when determining which to purchase. It’s imperative to look closely before you make any purchases, as making the right one is crucial for the operation of your machinery.