Mixed pole windings and some applications

When two polyphase AC windings of differing pole number are housed in a common AC machine stator, their separate MMFs combine additively in some regions of the machine and subtractively in others. The flux pattern consists of two components of short wavelength and small flux per pole, while the pattern of radial force between stator and rotor contains a component of long wavelength. This feature is the basis for an improved form of low speed rolling rotor machine and for the compliant-core machine in which the rotor deforms to make mechanical contact with the stator