Micro VFDs Gain Macro Features

Micro VFD considerations

There are few technical downsides to using a micro VFD in simple, lower-cost applications. A good rule to follow is if you are certain that you will never need to adjust the speed of a motor, then do not purchase a VFD. But if there is even a slight chance that the motor speed may need adjustment, then a newer, low-cost, high-feature VFD should be a top consideration.

Concerns might be the added size of a VFD compared to a contactor or starter, but some current models are palm size and consume about the same space as a motor contactor and overload combo (Figure 2). These micro VFDs have a built-in PLC, PID control, sensorless vector control, advanced network support, and I/O expansion—at a cost comparable to that of a motor contactor and overload combo—but with added benefits and reduced costs in other areas. They are available consolidated into a NEMA 4X package suitable for washdown areas (Figure 3).

OEM machines often use a small PLC controlling an across-the-line motor starter assembly. Traditional designs typically require three-phase power, but many end users want this machine to work in single-phase facilities. Instead of creating two separate designs, the OEM could replace the PLC and motor starter assembly with one newer VFD that can accept a single-phase power input. With this solution, the OEM solves the problem; costs are reduced; and there are fewer components and more potential customers.