A brushless permanent magnet motor has a rotor constructed of spaced
ferromagnetic backirons and a circumferential array of alternating
polarity magnetic poles that drive magnetic flux back and forth across an
armature air gap between the backirons. A stator includes an air core
armature in the air gap with three-phase windings. An inverter includes a
pulse-modulated semiconductor H-bridge that switches and regulates power
to the three-phase windings to drive the rotor. Harmonic losses in the
motor caused by ripple currents generated by the higher pulse switching
frequency in electronic variable speed drives, due to the inherently
lower inductance of air core motors, are substantially reduced by adding
serial inductance between the motor and drive. The H-bridge is serially
electrically connected to the three-phase armature windings through three
inductors that employ a low cost powder core. Each of the inductors
provides an inductance that is greater than twice the value of the leg
inductance of the three-phase windings.