One of the most prominent systems in modern industrial automation is the AC inverter duty motor and associated Variable Frequency Drive (VFD). From winding nonwoven fabrics onto cardboard cores for manufacturing N95 respirators to crushing granite boulders to pave the way for our first responders and truck drivers, the VFD plays a critical role in controlling AC motors across vast industries that make our communities strong today and better tomorrow.
While standard electro-mechanical motor starters and soft starters are relatively straight forward in terms of startup and commissioning, the VFD can require much more attention to process and application details in order to ensure a smooth and successful startup. For instance, in a fan or pumping application, the startup/commissioning process can be very straightforward with relatively short startup times. However, for applications such as camming, gearing, and tensioning, the process can become quite involved with a VFD where in-depth tuning and parameterization is often in play. Let’s have a look into the nuts and bolts of what is required for a successful VFD startup.
First off, we must have our fundamental motor information which is always found on the nameplate of the motor. We’re looking for the usual suspects here; motor voltage, motor rated amperage and motor rated horsepower to name a few. With this information in hand, it is now time to turn our attention to the wiring of the system. This is a very critical step, especially if the technician performing the startup did not wire/install the system. We’ll certainly want to double and even triple check that the line and load conductors are landed on the correct terminals. We’ve all heard the stories of line side conductors being landed to load side terminals of a VFD; it usually doesn’t end very well for the drive. I/O wiring needs to be inspected as well. You may see devices that need isolated grounding which has to be updated at startup. The best policy is to always verify all conductors for accurate landing/termination.
As for tools and PPE, make sure you have a nice set of tech screwdrivers, a digital multimeter, and all required PPE. It is always best practice to test your digital multimeter on a known live circuit to ensure your readings are accurate. We are all about safety and incorporating the appropriate and required PPE for any VFD startup. An extension cord can always come in handy as well. We’ve all been on a plant floor, production site, or in a commercial building with no readily available power for laptops and lights; it’s never ideal.
To continue our startup, we need to ensure that our parameters are set to correct values/selections for the application. Key considerations here are settings such as control methods. Are we using V/f control for a fan/pump application or a closed-loop vector control for tensioning fabric? VFD’s typically offer several control methods to suit various applications. Again, verification of the motor nameplate data is key here as well. It is also important to consider encoder counts, accel and decel times, and DC regen management.
Once the initial parameters are set, always perform some sort of drive to motor autotune. Did I mention ALWAYS? This is such a critical step in letting the drive get to know the motor. While it is ideal to perform a non-rotational autotune at minimum, it is always preferable to perform a rotational autotune, especially in applications requiring tight speed and position control. Additionally, perform a drive to motor autotune when replacing a motor, leads, the drive or even if the supply power has been modified. Now, with the drive operational and the motor spinning, what’s next? Riding off into the picturesque sunset of drive performance perfection? Not so fast partner! Time to bring in the faults!
Oh, the time honored, tried, and true VFD faults. We’ve all seen them, and we’ve all had to resolve them. While we can significantly decrease the potential for faults to arise on startup by performing methodical parameter selections and tuning(s), there is always the potential for faults to occur. Some of the more common faults are DC bus undervoltage – usually due to power cycling/loss, DC bus overvoltage – usually due to regen energy feeding back into the drive and over current which is often the outcome when a motor is overloaded. Phase-to-phase faults are also common. One key point to keep in mind here is that if your drive is calling out a ground fault, you really should investigate it.
At the end of the day, a successful VFD startup is all about preparation and patience. Having a solid understanding of the process at hand, sound knowledge of your drives’ capabilities, and patience when programming and tuning will certainly lay the framework for a thorough and successful VFD startup.