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How to choose the correct VFD?

When choosing variable frequency drives for an application it's critical to know exactly the purpose intended. There are so many variables. A fan application although simple enough can have many factors that can complicate a motor if not correctly sized or programmed.
Most vector VFDs can handle a fan application but the key is selecting and sizing a drive for long term and that will pose no unwanted spikes or heat production on both electric motor and the VFD drive.
Over-design was the name of that game as it is with most fan applications. All the better to use a VFD to supply only what you need and save energy.

You will find that if you operate a centrifugal fan in vector mode (or constant torque mode for that matter) you will operate at a higher current than in variable torque V/Hz. I tried it about 20 years ago and the current was 10-20% higher in vector mode with no significant improvement in operation.

Open-loop vector is, as much as anything, a marketing tool. Probably 90% of applications don't require it. But with the increase in microprocessor power and decrease in memory costs over the last couple of decades, it's become merely a matter of writing firmware for the variable frequency drive manufacturers to include it in their standard products. The option, as others have noted, to run in V/Hz mode is almost always there. Even ABB's flagship product, the ACS800 drive, has "scalar mode" which is V/Hz.

Rule of thumb to whether implementing vector control VFD is a good idea is whether you need very high starting torque. If not, then vector probably isn't necessary and V/Hz will work fine. If precise speed control really is necessary, you can get it with V/Hz and a speed feedback device (tach, resolver or encoder) but vector gives you very good speed control (about an order of magnitude better than open-loop V/Hz) without feedback. How precise do you need to be is critical.

Again, as others have noted, pumps and fans really don't require vector control (unless you're running a peristaltic metering pump and want to precisely control flow, for example.) And, again as others have noted, vector mode tends to be less efficient in these applications, costing you money.

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