Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 242)

242 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 4 Motor Control
take advantage of inherent advantages. In principle, there are no size limitations
to IPM designs and these can be developed from small fractional horsepower to
large – hundreds of Hp ratings, creating potential applications that can benefit
from variable speed IPM control.
Synchronous Reluctance Motors
P35 [Motor Ctrl Mode] induction motor options.
• 7 = “SyncRel VHz”
• 8 = “SyncRel SV”
Synchronous reluctance motors have an equal number of stator and rotor poles.
The projections on the rotor are arranged to introduce internal flux “barriers,”
holes which direct the magnetic flux along the so-called direct axis. Typical
numbers of poles are 4 and 6. Following example of a 4 pole rotor and 6 pole
stator.
As the rotor is operating at synchronous speed and there are no current-
conducting parts in the rotor, rotor losses are minimal compared to those of an
induction motor, thus potential energy savings in appropriate applications. Once
started and rotating at synchronous speed, the motor can operate with sinusoidal
voltage. So to start and control speed at frequencies other than utility requires a
variable-frequency drive.
AC Linear Electric Motors LIMs and LSMs
P35 [Motor Ctrl Mode] induction motor options.
• 0 = “Induction VHz”
• 9 = “Adjustable Voltage”
The first linear electric motor was conceived by Wheatstone more than 100 years
ago. But large air gaps and low efficiencies prevented linear electric motors from
being widely used until recent advances in design and VFD controls.
Linear Induction Motors (LIMs)
In a LIM, the motor stator creates an Alternating Current (AC) field that induces
currents into the reaction plate (moving element), which is typically an
aluminum fin or plate. This creates eddy currents in the moving element which
react with the moving field in the stator to produce thrust. LIMs typically are
kept moving, avoiding holding stationary (equivalent to locked rotor) because of
significant heating of the reactor plate.