Methods and apparatus provide for: commutating windings of a polyphase machine such that electromagnetic fields of stator and rotor phases of the polyphase machine produce at least one of motoring and generating torque; providing a first rotor excitation voltage having substantially no DC component when...http://www.google.com/patents/US7116073?utm_source=gb-gplus-sharePatent US7116073 - Methods and apparatus for controlling a motor/generator
