This is more or less the same as the NOLA circuit though. Lower the motor voltage and reduce the iron losses. If you reduce the iron losses you increase the efficiency of the motor.
The losses in a motor should go down as the load decreases. One of the losses is the copper resistance I^2xR losses in the stator windings. As you reduce the load you reduce the stator current. Less stator current produces less heating in the stator windings.
The output voltage waveform of a VFD will increase the losses of the motor or energy used by the motor. The energy savings due to reducing the voltage can be very small at times unless the motor is running below about 25% load. So, installing a VFD to reduce energy use with this voltage reduction feature could actually increase your energy use.
The common and blantant use of "energy savings" to sell a product need to always be considered in details. Mostly, I see VFD's as being useful for process control where you need a certain pressure or flow and for use in places where the efficiency of a process can be optimized due to poor initial component selection.
Basically, the marketplace has too much focus on simply reducing the cost to run the motor and not enough on reducing the cost to get the work done. Of course, it is easier to focus on how VFD's will reduce the energy going into a motor and much harder to show how it will make the whole process more efficient.
For example, if you are pumping water, you want to focus on reducing the energy cost per gallon of water pumped, not to focus on reducing the cost per hour to run the motor turning the pump. Lowering the speed of a water pump can easily reduce the efficiency of the whole pumping system which increases your cost per gallon of water pumped.
