How to Program a VFD: A Basic Guide
- Verify there is nothing between the motor and the drive, such as a disconnect without a make-before-break configuration. If there is a safety requirement, you should consider a drive with a STO (safety torque off) feature to ensure that an emergency stop can be performed directly by the VFD.
- Verify that the motor itself is in proper operating condition. You could use a Megger (megohmmeter) to assess the insulation on wiring and motor windings to ensure safe working conditions for your motor as a first step.
If you’ve just received your variable frequency drive (VFD) and are looking to get it set to run, there are some general guidelines and instructions you need to follow to ensure that the VFD operates smoothly with your motor system. In programming your drive, here are the main steps you should take to ensure a successful operation.
Does VFD programming vary by drive?
Not all VFDs are created equal. There are countless brands and features that can create differences in the specifics of how you set up and program your drive, and the capabilities of your drive can also vary widely. That’s why our guide won’t get into the weeds on each key you press or application you run. That will change based on your equipment.
Ultimately, our guide should not replace the need for you to read the instruction manual coming with your VFD. Rather, here is our educated guidance on the essential points to accomplish in your programming.
VFD Programming Instructions
As a best practice, before you get started on programming, you really should double and triple-check that your system, as a whole, is installed correctly. This includes everything from the line to the VFD and down to the motor. Many service calls and “programming issues” actually begin with an installation issue that was neglected or done incorrectly before programming ever started.
When checking installation:
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Enter your motor’s data in the VFD’s interface.
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Check the direction your motor is turning.
It can be difficult to determine which direction your motor will spin on startup without testing it first. You obviously will want to know which way the connections should be implemented. Test run the VFD to ensure the motor is spinning in the right direction.
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Input the basic parameters the motor should run on.
- Minimum/maximum speed A VFD allows parameters for minimum and maximum speed settings for the motor in order to increase its efficiency, control processes, and reduce costs associated with wearing the motor out.
- Desired set speed This can also be referred to as a speed reference in VFD engineering. The more accurate a VFD’s speed reference is, the better the VFD can do at meeting system demand. Keep in mind when setting that your speed reference is still in harmony with safe parameters for running the motor.
- Acceleration/deceleration times Your VFD controls the motor’s time to get from 0 Hz to maximum output frequency, and often from the max back to 0.
- Mode of control Setting up the controls on your VFD will be the last basic step of your VFD programming (Step 5 in this guide), but your controls are also one of the parameters that need programming before setup occurs.
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Consider your VFD’s application.
On this step, things could get a little more specific to your particular drive. Many VFDs are dual-rated for variable-torque and constant-torque applications. Typically, there are parameters to define the overload characteristics required for the application.
- Fans and Pumps You’ll want a longer acceleration and deceleration time for fan and pump applications. You’d also probably look to implement a catch-on-fly function and coast-to-stop function to prevent overcurrent and overvoltage faults. Catch-on-fly, also called flying start or catch-a-spinning-load, enables the VFD to start controlling the motor while it is already spinning, and coast-to-stop lets the VFD turn off and allows the motor’s inertia to stop it gradually.
- Compressors Typically, with compressors, you want a quicker acceleration. Compressors often start unloaded, so you want the motor to start as quickly as the manufacturer safely recommends.
- Elevators/Conveyors/Cranes With applications like these, it’s best to call an expert if you’re not familiar with the programming, as you likely will deal with regenerative power and braking issues.
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Set up controls.
Many VFDs are controlled externally rather than directly via the keypad. The most common external controls are performed through the digital and analog input/output (IO) that comes standard with most drives.
To program your VFD:
This information will be found on your motor nameplate. Mimic the information on your motor nameplate into the VFD, such as speed, voltage, horsepower rating (HP), amperage rating (A), frequency (Hz), and overload protection. This allows the VFD to understand the necessary V:Hzratio when running the motor. While your drive is designated to a certain performance level, it doesn’t inherently know how to apply to your system without that data input.
If the motor’s direction does need to be changed, you can program that change through the VFD’s parameters, but the easier way is to switch any two of the three output leads going to the motor. Changing all three may not result in a change of direction for the motor.
Just like that, you’ve gotten your motor working in the right direction while eliminating the hassle of extra programming.
Here are some of the main parameters you’ll need to set with your drive:
On both ends of the speed range, it’s important to set safe parameters to prevent overcurrent and overheating of the motor. Many motors are TEFC (totally enclosed, fan-cooled) which means the fan is attached to the rotor and is directly proportional to the speed of the motor. If the motor is running too slow, the fan won’t be running fast enough to keep the motor from overheating. Energy savings are possible by making a modest allowance for speed decreases within a range that keeps airflow actually blowing through the fan, but it’s a steep drop-off in effectiveness if going slower than ¼ of the total RPM.
On the other side of the range, the maximum speed of your motor can be programmed, but it’s important to keep the mechanical components and the torque rating of your motor in mind. If the max speed is too fast, your motor bearings are likely going to wear out from not being lubricated enough to handle it. The high speed will also cause a loss of torque. There is also the issue of vibration, which can become an issue if the motor is running over 100% of the rated speed, leading to heat stress on several components.
Electric motors, without any parameters in place, are made to start at full speed. Without a VFD or soft starter, the motor will demand 600% of the rated current as an inrush current during acceleration, which is highly inefficient and can damage the motor over time.
In some applications, engineers will implement a soft starter to reduce the inrush current by half, but a VFD goes beyond a soft starter’s capabilities by controlling the entire acceleration process.
In some cases, you may also want to control the deceleration process. Although this is possible, you often need a plan to deal with the regenerated energy. You can prevent overvoltage issues by increasing the deceleration time or by introducing break resistors to the VFD to electronically break the motor.
What if I need more help?
Good work programming your VFD. If all goes well, the drive should proceed to function properly on startup. If not, it never hurts to reset the VFD to the factory defaults and start again.
Some troubleshooting could be necessary if more programming is needed beyond the basics, in which case, it’s best to contact an expert for service help. That’s where VFDs.com can come in.
As consultative experts, our representatives can assist you with specific technical questions and issues by phone by calling 1-800-800-2261. You can also submit any questions you have through our contact form, or you can open a chat with an expert by hitting the chat bubble on the bottom right of this window.