Dual phase resolver to digital converter

A method of detecting rotor shaft position using a resolver having a rotor with a rotor winding and a stator with first and second stator windings, said method comprising the steps of:

• a) exciting said first stator winding with a sinewave type signal and exciting said second stator winding with a cosinewave type signal;
• b) measuring a first phase shift between a rotor signal produced by the rotor winding and the sinewave type signal and detecting when said first phase shift is subject to error;
• c) measuring a second phase shift between the rotor signal and the cosinewave type signal and detecting when said second phase shift is subject to error;
• and
• d) providing an indication of said rotor shaft position which is based upon said first phase shift when the second phase shift is subject to error, and which is based upon when the first phase shift is subject to error.

In a rotor position detection system including a resolver having a rotor with a rotor winding and a stator with first and second stator windings and including means for exciting said first stator winding with a first reference signal and exciting said second stator winding with a second reference signal, the improvement comprising:

• means for measuring a first phase shift of a rotor signal produced by said rotor winding with respect to the first reference signal and detecting when said first phase shift may be subject to error;
• means for measuring a second phase shift of the rotor signal with respect to the second reference signal and detecting when said second phase shift may be subject to error;
• means for producing an averages phase shift by averaging said first and second phase shifts after displacing one of said first or second phase shifts by an angular amount sufficient for said first and second phase shifts to be in phase with each other;
• and
• means for providing a shaft position output from said detection system, the shaft position output being based upon said first phase shift when said second phase shift may be subject to error, the shaft position output being based upon said second phase shift when said first phase shift may be subject to error, and the shaft position output being based upon said averaged phase shift when neither said first phase shift nor said second phase shift may be subject to error.