Rotor position detection at standstill and low speeds using a low power permanent magnet machine

For a multiphase alternating current (AC) wound field synchronous machine (WFSM) that has a stator with a selected number of poles, the WFSM having an associated exciter and multiphase AC permanent magnet machine (PMM) directly coupled to the WFSM, a method of sensing the position of a rotor in the WFSM comprising the steps of:

• configuring a stator for the PMM to have a number of poles that is a sub-multiple of the selected number of WFSM stator poles;
• inducing geometric saliency in a rotor for the PMM;
• applying multiphase AC power of a selected frequency to the PMM stator;
• detecting the negative first harmonic and the positive second harmonic stator currents of the multiphase AC power frequency;
• converting the detected PMM negative first harmonic and the positive second harmonic stator currents from their multiphase coordinates to αβ coordinates;
• rotating the converted PMM negative first harmonic and the positive second stator currents into their respective reference frames to generate respective αβ coordinate harmonic current vectors;
• estimating north-south polarity of the WFSM rotor with the αβ coordinate positive second harmonic current vectors and
• estimating the polarity-determined position of the WFSM rotor based on the values of the negative first harmonic αβ coordinate harmonic current vectors.

For a multiphase alternating current (AC) wound field synchronous machine (WFSM) that has a stator with a selected number of poles, the WFSM having an associated exciter and multiphase AC permanent magnet machine (PMM) directly coupled to the WFSM, a method of sensing the position of a rotor in the WFSM comprising the steps of:

• configuring a stator for the PMM to have a number of poles that is a sub-multiple of the selected number of WFSM stator poles;
• inducing saturation saliency in a rotor for the PMM;
• applying multiphase AC power of a selected frequency to the PMM stator;
• detecting at least the positive second harmonic stator currents of the multiphase AC power resulting from the rotor saliency;
• converting the detected PMM positive second harmonic stator currents from their multiphase coordinates to αβ coordinates;
• rotating the converted PMM positive second harmonic stator currents into their reference frame to generate αβ coordinate positive second harmonic current vectors;
• and
• estimating the position of the WFSM rotor based on the values of the αβ coordinate positive second harmonic current vectors.