Patent ID: 7135829

Claim:
An apparatus, comprising: a driver circuit operable to commutate windings of a polyphase machine in response to commutation control signals; and a controller operable to produce the commutation control signals such that electromagnetic fields of stator phases of the polyphase machine at least lead electromagnetic fields of rotor phases of the polyphase machine to produce motoring torque, wherein the controller is operable to automatically vary a lead angle measured between the electromagnetic fields of the stator and rotor phases as a function of respective ranges of rotational speeds of the polyphase machine, a first range of rotational speeds being established by: (i) determining a first torque versus speed envelope for the polyphase machine using a fixed first lead angle; (ii) determining a second torque versus speed envelope for the polyphase machine using a fixed second lead angle; and (iii) determining a difference between an initial speed and a final speed substantially at which the first and second torque versus speed envelopes intersect.