Patent ID: 6989648

Claim:
An electrical motor system comprising: a rotor and a stator, the stator having poles facing circumferential surfaces of the rotor so that the stator forms a magnetic circuit with the rotor, the stator further having stator coils grouped into one or more phase windings, which phase windings are separately energizable to induce stator magnetic fields which interact with magnetic fields of the rotor; voltage detecting means for detecting a voltage across the or at least one stator phase winding; and processing means for determining from one or more voltage measurements the rotor flux linking said stator phase winding, or a value which is a function of the rotor flux linkage, when the excitation current in said stator phase winding is at a known point in its cyclic variation chosen to substantially eliminate from the rotor flux or said function inductive and/or resistive contributions, and for determining from the rotor flux linkage or said function thereof the load angle of the motor, wherein the voltage detecting means or processing means receives timing signals identifying each occurrence of the known point.