Allen-Bradley AFD vs VFD explained in detail. Learn the difference between AFD and VFD terminology, PowerFlex drive types, control methods, PLC integration, applications, and selection.
Understanding the Differences Between Adjustable Frequency Drives and Variable Frequency Drives: Terminology, Applications, and PowerFlex Insights.
Allen-Bradley AFD and VFD generally describe the same fundamental class of AC motor-control technology: an electronic drive that varies motor frequency and voltage to control speed and torque. The practical difference is primarily terminology and application context rather than two fundamentally different types of PowerFlex hardware, because Rockwell Automation uses both “Adjustable Frequency Drive” and “Variable Frequency Drive” terminology across its documentation and product portfolio. For engineers selecting an Allen-Bradley PowerFlex drive, the important questions are the motor type, horsepower, voltage, load profile, control method, overload requirement, braking, communications, safety functions, and application environment—not simply whether the catalog calls the product an AFD or VFD.
When engineers search for Allen-Bradley AFD vs VFD, they are often expecting two different technologies. That assumption causes unnecessary confusion.
The reality is considerably simpler.
In Allen-Bradley terminology, an AFD (Adjustable Frequency Drive) is an electronic motor controller that adjusts the frequency and voltage delivered to an AC motor. A VFD (Variable Frequency Drive) performs the same fundamental function. In many industrial applications, the terms are used interchangeably.
Rockwell Automation’s PowerFlex family illustrates this clearly. Rockwell’s documentation describes products such as the PowerFlex 4M as Adjustable Frequency AC Drives, while its current product portfolio prominently uses Variable Frequency Drives (VFDs).
So, if you are trying to determine whether an Allen-Bradley AFD is fundamentally different from an Allen-Bradley VFD, the short answer is no. The meaningful differences occur between specific drive families, control architectures, ratings, options, and application capabilities.
What Is an Allen-Bradley AFD?
An Adjustable Frequency Drive is a power-electronics device used to control an AC motor by adjusting the electrical frequency and voltage supplied to the motor.
The term emphasizes the drive’s ability to adjust frequency.
For example, a motor designed to operate around 60 Hz can be operated at a lower frequency when the process requires lower speed. The drive can ramp the motor from zero speed to the commanded operating speed rather than applying full line frequency immediately.
This provides much more control than a conventional across-the-line starter.
A typical AFD contains several fundamental sections:
An AC input section
A rectifier
A DC bus
An inverter section
Control electronics
Protection and monitoring circuitry
Communications and I/O interfaces
The incoming AC power is converted into DC through the input rectifier. The DC bus then supplies the inverter stage, which uses switching devices to synthesize the controlled output waveform delivered to the motor.
The controller determines the appropriate switching pattern based on the desired speed, torque, current, voltage, motor parameters, and selected control algorithm.
This architecture is the foundation of modern PowerFlex drives.
Rockwell’s PowerFlex documentation demonstrates that adjustable-frequency drives can support different control methods, including V/Hz and sensorless vector control, depending on the drive family.
Why Is It Called an Adjustable Frequency Drive?
The name comes directly from the operating principle.
An AC motor’s synchronous speed is related to supply frequency:
Ns = 120 × f / P
Where:
Ns = synchronous speed in RPM
f = electrical frequency in Hz
P = number of motor poles
Therefore, changing frequency changes the motor’s operating speed.
A 4-pole motor operating from a 60 Hz supply has a synchronous speed of 1,800 RPM. If the frequency is reduced, synchronous speed also decreases.
The actual motor shaft speed will normally be slightly lower because of slip in an induction motor.
The drive therefore provides an electronic method of changing motor speed without mechanically changing gears, pulleys, or sheaves.
What Is an Allen-Bradley VFD?
A Variable Frequency Drive is an electronic controller that varies the frequency and typically the voltage supplied to an AC motor.
That definition is fundamentally the same as the definition of an AFD.
Rockwell Automation describes its Allen-Bradley PowerFlex portfolio as VFD technology capable of controlling motor speed, torque and direction, with products ranging from compact drives to sophisticated high-performance systems.
VFD is arguably the terminology most commonly encountered today when engineers discuss AC motor speed control.
You will also encounter related terms such as:
AC drive
Adjustable speed drive (ASD)
Adjustable frequency drive (AFD)
Variable speed drive (VSD)
Variable frequency drive (VFD)
Frequency inverter
AC inverter
These terms are not always perfectly synonymous in every manufacturer’s documentation, but in everyday industrial automation discussions, AFD and VFD commonly refer to the same basic category of AC motor drive.
Automation Pioneer similarly describes VFDs as electronic controllers that regulate motor speed and torque by adjusting frequency and voltage. (Understanding Variable Frequency Drives (VFDs))
Allen-Bradley AFD vs VFD: What Is the Actual Difference?
The most important distinction is this:
AFD and VFD are primarily different names for the same fundamental technology, not two separate Allen-Bradley product technologies.
The term AFD emphasizes adjustable frequency.
The term VFD emphasizes variable frequency.
Both refer to drives that electronically control AC motor operation by manipulating output frequency and voltage.
| Feature | Allen-Bradley AFD | Allen-Bradley VFD |
|---|---|---|
| Basic technology | AC motor drive | AC motor drive |
| Frequency control | Yes | Yes |
| Motor speed control | Yes | Yes |
| Voltage control | Typically yes | Typically yes |
| Torque control | Depending on drive/control mode | Depending on drive/control mode |
| Typical application | Industrial motor control | Industrial motor control |
| PowerFlex compatibility | Yes | Yes |
| PLC integration | Available | Available |
| EtherNet/IP | Available on applicable models | Available on applicable models |
| V/Hz control | Available on applicable models | Available on applicable models |
| Vector control | Available on applicable models | Available on applicable models |
The table does not mean every Allen-Bradley drive has identical functionality. That would be a serious engineering mistake.
A PowerFlex 4M, for example, is not equivalent to a PowerFlex 755T simply because both can be described as AFDs or VFDs.
The drive family determines the actual capabilities.
Why Rockwell Uses Both AFD and VFD Terminology
This is where much of the confusion originates.
Rockwell Automation has historically used Adjustable Frequency AC Drives in PowerFlex documentation. The PowerFlex 4M, for example, is formally documented as an Adjustable Frequency AC Drive.
At the same time, Rockwell’s modern website organizes its drive portfolio under Variable Frequency Drives (VFDs).
There is therefore no contradiction.
The terminology has evolved with the industry.
If you search for:
Allen-Bradley AFD
you may find PowerFlex technical documentation.
If you search for:
Allen-Bradley VFD
you will find PowerFlex products, application information, and product categories.
Both searches can lead you to the same fundamental technology.
The important engineering task is identifying the correct PowerFlex catalog number and drive architecture.
How Does an Allen-Bradley AFD/VFD Work?
Understanding the power conversion process makes the terminology much easier to understand.
Step 1: AC Power Enters the Drive
The drive receives AC power from the facility electrical system.
Depending on the model, this may be single-phase or three-phase power at different voltage classes.
The drive must be correctly matched to the available input voltage.
For example, a PowerFlex drive designed for a 480 V-class application cannot simply be treated as interchangeable with a 240 V-class drive.
Input voltage, phase configuration, current rating, fault current, and installation requirements all matter.
Step 2: The Rectifier Converts AC to DC
The input rectifier converts incoming AC power into DC.
This creates the DC link used by the inverter section.
The rectifier topology can vary according to drive design and power level.
Step 3: The DC Bus Stores and Conditions Energy
The DC bus provides the intermediate energy path between the rectifier and inverter.
Capacitors and associated circuitry smooth the DC voltage.
This section is also important during troubleshooting because excessive DC bus voltage, undervoltage, ripple, or abnormal charging behavior can indicate different electrical problems.
Step 4: The Inverter Creates Controlled AC Output
The inverter uses semiconductor switching devices to convert the DC bus into a controlled three-phase output.
The controller determines the switching pattern.
By changing output frequency and voltage, the drive controls motor operation.
Modern drives can go considerably further than basic frequency adjustment.
Depending on the PowerFlex family, the controller can provide sophisticated control of:
Speed
Torque
Acceleration
Deceleration
Current
Motor flux
Position
Regeneration
Safety functions
Communications
Diagnostics
Rockwell’s PowerFlex 755T family, for example, incorporates advanced control technology, predictive diagnostics, harmonic mitigation, Safe Torque Off and other capabilities intended for demanding applications.
AFD vs VFD: The Control Methods Matter More Than the Name
When selecting an Allen-Bradley drive, engineers should stop focusing on whether the product is called an AFD or VFD.
The more important question is:
How does the drive control the motor?
V/Hz Control
V/Hz, or volts-per-hertz control, is one of the simplest drive control methods.
The drive maintains an appropriate relationship between voltage and frequency.
This works well for many applications such as:
Pumps
Fans
Conveyors
Blowers
Basic machinery
HVAC equipment
It is straightforward and often economical.
The limitation is that it generally does not provide the same level of torque regulation and dynamic response available from advanced vector-control strategies.
Sensorless Vector Control
Sensorless vector control provides more sophisticated control of motor flux and torque without necessarily requiring an encoder.
This can provide stronger low-speed performance and better speed regulation than basic V/Hz control.
Rockwell documentation for the PowerFlex 40P, for example, identifies both V/Hz and sensorless vector control capabilities.
This type of control is useful when the application requires more than simply adjusting motor speed.
Closed-Loop Vector Control
Closed-loop vector systems use feedback, typically from an encoder or other feedback device.
The drive can compare commanded speed with actual motor behavior and make corrections.
This can be important for applications requiring tight speed regulation, torque control, or positioning performance.
The specific feedback hardware and drive capability must be evaluated against the application.
Allen-Bradley PowerFlex Drives: AFD vs VFD in the Real World
The PowerFlex family contains drives for widely different applications.
That means the phrase “Allen-Bradley VFD” alone is not sufficient for selecting a drive.
You need to identify the application and required performance.
PowerFlex Compact Drives
Compact PowerFlex products target machine-level applications where space, simplicity and ease of installation are important.
Rockwell describes the PowerFlex 4M as a compact adjustable-frequency AC drive intended for machine-level speed control and applications where space savings and ease of programming are important.
These drives can be appropriate when the machine does not require advanced drive functionality.
PowerFlex General-Purpose Drives
General-purpose PowerFlex drives offer more functionality and application flexibility.
The exact features vary by series, but applications can include conveyors, pumps, fans, machine tools and other industrial equipment.
PowerFlex Architecture-Class Drives
Higher-end PowerFlex drives support more sophisticated integration and control.
Depending on the series, this may include:
Advanced motor-control algorithms
Feedback
Regeneration
Networking
Safety
Advanced diagnostics
Motion-related functionality
Harmonic mitigation
High-performance control
The PowerFlex 755T is an example of a high-performance platform with advanced control, predictive diagnostics, harmonic mitigation and integrated EtherNet/IP capabilities.
Allen-Bradley AFD/VFD Integration With PLCs
One of the biggest advantages of a modern PowerFlex drive is its ability to become part of the larger automation architecture.
A drive does not have to operate as an isolated device.
It can exchange information with a PLC, HMI, SCADA system, safety system, and plant network.
Rockwell specifically highlights integration between Allen-Bradley VFDs and Logix programmable logic controllers. Its Premier Integration approach allows drive configuration and controller/network integration within the broader Logix environment.
For an industrial automation system, this can mean the PLC sends commands such as:
Start
Stop
Forward
Reverse
Speed reference
Torque reference
Reset
The drive can return:
Actual speed
Output current
Output frequency
Drive status
Fault status
Alarm information
Motor load
Diagnostic information
With networked control, this information becomes available to the automation system rather than remaining on the drive keypad.
That distinction matters enormously in modern plants.
A drive that simply changes motor frequency is useful.
A drive that participates intelligently in the control architecture is far more capable.
EtherNet/IP and PowerFlex Drives
EtherNet/IP is particularly important in Allen-Bradley systems.
PowerFlex drives can use communications to exchange command and status information with Logix controllers.
That reduces the need for extensive hardwired control wiring and gives the PLC access to drive information.
However, engineers should not assume that every PowerFlex model has identical networking capabilities.
Some models have integrated communications, while others may require an option module or different architecture.
Always verify the exact catalog number.
Rockwell’s current VFD portfolio specifically highlights integration with PLCs and communications as core features of its PowerFlex architecture.
For additional industrial automation context, see Automation Pioneer’s resources on Programmable Logic Controllers (PLCs).
AFD vs VFD Applications
Because AFD and VFD generally describe the same technology, application differences are determined by the drive and motor system rather than the terminology.
Pumps
VFDs are widely used on pumps because flow requirements frequently change.
Rather than operating the motor continuously at full speed and controlling flow through throttling, the drive can reduce motor speed when process demand falls.
That can improve process control and reduce energy consumption.
Fans and Blowers
Fans frequently operate under variable-load conditions.
A properly selected drive can adjust motor speed to match required airflow.
This makes VFD control particularly useful in HVAC and industrial ventilation systems.
Conveyors
Conveyors can benefit from controlled acceleration and deceleration.
Instead of starting a motor abruptly, the drive can ramp the motor to operating speed.
That reduces mechanical shock and can improve product handling.
Compressors
Compressors can require sophisticated control depending on the process.
The correct drive selection must consider compressor type, operating range, starting torque, speed range, bypass requirements, harmonic considerations and manufacturer requirements.
Machine Tools
Machine tools can demand much greater control performance.
The engineer may need to consider:
Speed regulation
Torque response
Low-speed operation
Feedback
Acceleration/deceleration
Braking
Positioning
A basic compact drive may therefore be inappropriate even though it is technically a VFD.
For application-specific requirements, Automation Pioneer Industries We Serve provides additional context around manufacturing, oil and gas, water treatment, pharmaceutical, food and beverage, aerospace, energy, and other industrial applications.
How to Choose the Right Allen-Bradley PowerFlex AFD/VFD
The correct selection process starts with the motor and application—not the drive name.
1. Identify Motor Voltage
Determine the motor’s rated voltage from the nameplate.
Common industrial motor voltages include:
208 V
230 V
460 V
480 V
575 V
Do not select a drive based solely on horsepower.
Voltage matters.
2. Determine Motor Full-Load Current
Motor FLA is often more important than horsepower when determining drive capacity.
Compare the motor’s full-load current against the drive’s rated output current.
Do not simply assume that a “10 HP drive” is suitable for every 10 HP motor.
Different motors can have different current requirements.
3. Identify the Load Type
Determine whether the application is:
Variable torque
Constant torque
Heavy duty
High overload
High starting torque
Regenerative
High inertia
A fan application and a conveyor application may require very different drive selection criteria even if the motors have identical horsepower ratings.
4. Determine Required Speed Range
Ask how slowly the motor must operate.
A motor that only needs to operate from 30–60 Hz is a very different application from one that needs stable operation at extremely low speed.
5. Determine Torque Requirements
This is critical.
If the machine requires high torque at low speed, basic V/Hz control may not be sufficient.
Vector control or feedback may be necessary.
6. Evaluate Braking
If the load has significant inertia or must decelerate rapidly, determine whether braking is required.
Options may include:
Dynamic braking
Regenerative braking
Mechanical braking
The correct solution depends on the application.
7. Determine Communications
If the drive will integrate with an Allen-Bradley PLC, determine whether the system requires:
EtherNet/IP
Hardwired I/O
Analog reference
Digital reference
Other industrial communication protocols
8. Evaluate Safety Requirements
Modern drive systems can include safety functionality such as Safe Torque Off.
Rockwell identifies Safe Torque Off and Safe Speed Monitor options among capabilities available in its higher-performance PowerFlex portfolio.
Safety functions must be evaluated as part of the machine’s overall safety architecture rather than treated as an isolated drive feature.
Common Mistakes When Comparing Allen-Bradley AFDs and VFDs
Mistake 1: Assuming AFD and VFD Are Different Technologies
This is the most common mistake.
In most Allen-Bradley AC-drive discussions, AFD and VFD describe the same fundamental technology.
The important comparison is between specific PowerFlex models.
Mistake 2: Selecting by Horsepower Alone
A 20 HP motor does not automatically mean any 20 HP PowerFlex drive will work.
Check:
Voltage
FLA
Duty
Overload
Ambient temperature
Altitude
Enclosure
Carrier frequency
Application type
Mistake 3: Ignoring the Motor Nameplate
The motor nameplate should be treated as primary selection data.
At minimum, verify:
Voltage
Current
Frequency
RPM
Power
Service factor
Motor type
Rockwell’s PowerFlex 40 documentation, for example, includes motor nameplate parameters such as rated voltage, rated frequency and motor overload current among drive setup parameters.
Mistake 4: Treating Every PowerFlex as Equivalent
PowerFlex is a family—not a single drive.
A compact drive designed for simple machine control should not be treated as interchangeable with a high-performance architecture-class drive.
Mistake 5: Ignoring the Mechanical System
The drive is only one component.
You also need to consider:
Gearboxes
Couplings
Bearings
Belts
Pumps
Fans
Conveyors
Brakes
Mechanical resonance
Changing motor speed can change the mechanical behavior of the entire system.
AFD vs VFD vs Soft Starter
Another common search-intent question is whether a VFD is simply a more sophisticated soft starter.
It is not.
A soft starter primarily controls motor starting and stopping by controlling voltage during those events.
A VFD controls motor frequency and voltage, allowing continuous speed control during operation.
Therefore:
Soft starter = controlled starting/stopping
VFD/AFD = continuous variable-speed motor control
A soft starter can be the right choice when the motor normally needs to operate at full speed but the plant wants reduced starting stress.
A VFD is appropriate when the process requires variable speed.
The selection should therefore be based on the process requirement rather than assuming that one technology is universally better.
Does an Allen-Bradley VFD Save Energy?
It can, but engineers should avoid claiming automatic energy savings in every application.
Energy savings depend heavily on the load.
The opportunity is particularly significant in variable-torque applications such as centrifugal pumps and fans, where reducing speed can dramatically reduce power requirements.
Rockwell explicitly identifies energy reduction as one of the applications for its PowerFlex VFD portfolio, particularly where motor speed can be matched to demand.
However, the drive itself also consumes energy.
Therefore, a proper engineering evaluation should consider:
Motor efficiency
Drive efficiency
Operating hours
Load profile
Speed profile
Process requirements
Existing control method
Electricity cost
For more information, see Automation Pioneer’s Variable Frequency Drives (VFD).
Troubleshooting an Allen-Bradley AFD/VFD
When a PowerFlex drive faults, do not immediately replace the drive.
First determine whether the fault originates from the:
Incoming power
Motor
Mechanical load
Control system
Drive parameters
Communications network
Drive hardware
Common fault conditions can involve:
Overcurrent
Overvoltage
Undervoltage
Overtemperature
Motor overload
Ground fault
Communication loss
Encoder/feedback problems
Incorrect motor parameters
A fault code is a diagnostic starting point, not automatically the root cause.
For example, an overcurrent fault may result from excessive mechanical load, acceleration that is too aggressive, an incorrect motor configuration, a short circuit, or other conditions.
That is why troubleshooting should begin with the fault history and operating conditions.
AFD vs VFD: The Bottom Line for Allen-Bradley Users
If you remember only one thing from this guide, remember this:
An Allen-Bradley AFD and VFD are generally two terms for the same fundamental class of AC motor drive.
The terminology is not where the engineering decision lies.
The real decision is which PowerFlex drive architecture fits the application.
For a simple machine, a compact PowerFlex drive may be sufficient.
For a demanding conveyor, pump, compressor, extruder, machine tool or process-control application, the engineer may need higher overload capacity, vector control, feedback, braking, communications, safety functions or advanced diagnostics.
Rockwell’s PowerFlex portfolio spans this range, from compact adjustable-frequency drives through sophisticated VFD platforms with advanced control and diagnostics.
So when someone asks:
“Should I use an Allen-Bradley AFD or VFD?”
the technically correct response is to ask a better question:
“Which Allen-Bradley PowerFlex drive meets the motor, load, control, safety, communications and environmental requirements of the application?”
That is the comparison that actually matters.
10 Frequently Asked Questions About Allen-Bradley AFD vs VFD
1. Is an Allen-Bradley AFD the same as a VFD?
Generally, yes. In Allen-Bradley industrial drive terminology, an Adjustable Frequency Drive and Variable Frequency Drive refer to the same fundamental category of electronic AC motor controller.
2. What does AFD stand for in Allen-Bradley?
AFD stands for Adjustable Frequency Drive. Allen-Bradley PowerFlex documentation uses the term Adjustable Frequency AC Drive for various products.
3. What does VFD stand for?
VFD stands for Variable Frequency Drive. It is an electronic device that controls AC motor speed and torque by varying output frequency and voltage.
4. Is PowerFlex an AFD or VFD?
PowerFlex drives can accurately be described using both terms depending on the specific Rockwell documentation and context. Rockwell currently presents its PowerFlex portfolio under Variable Frequency Drives while many technical documents use Adjustable Frequency AC Drives.
5. Does a VFD control motor speed?
Yes. A VFD controls AC motor speed primarily by changing the frequency of the electrical power supplied to the motor.
6. Can an Allen-Bradley VFD control torque?
Yes, depending on the drive and control method. Basic V/Hz control provides less sophisticated torque regulation than vector-control architectures.
7. Can an Allen-Bradley PowerFlex drive communicate with a PLC?
Yes. Applicable PowerFlex drives can integrate with Allen-Bradley Logix PLC systems using communications such as EtherNet/IP, depending on the specific drive and configuration.
8. Is a PowerFlex drive better than a soft starter?
They solve different problems. A soft starter primarily manages motor starting and stopping, while a VFD provides continuous variable-speed control.
9. How do I choose the right Allen-Bradley PowerFlex drive?
Start with motor voltage, motor full-load current, horsepower, load type, overload requirements, speed range, torque requirements, braking, feedback, communications, safety requirements and environmental conditions.
10. What is the biggest difference between Allen-Bradley AFD and VFD?
For most applications, there is no fundamental technology difference. The important differences are between the individual PowerFlex drive families and their available control, power, communication, safety, feedback and application capabilities.
Recommended Automation Pioneer Resources
To deepen your understanding of industrial automation, critical factory infrastructure, and digital transformation, explore these related resources on Automation Pioneer:
- AC Adjustable Frequency Drives
- Allen-Bradley AC Adjustable Frequency Drives
- Allen-Bradley PowerFlex AC drives
- Allen-Bradley PowerFlex 525 AC drive
- PowerFlex 753 vs 755
- Allen-Bradley AFD selection guide
- Allen-Bradley PowerFlex programming
- Allen-Bradley PowerFlex Troubleshooting
- Allen-Bradley PowerFlex EtherNet/IP
- Allen-Bradley AFD vs VFD
- Allen-Bradley AFD Applications
These articles offer additional technical insights into the automation, networking, monitoring, and control technologies that support modern industrial automation and mission-critical infrastructure.
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