Surface permanent magnet synchronous machine design for saliency-tracking self-sensing position estimation at zero and low speeds

Elimination of externally mounted position sensors and their associated cables is a goal for virtually all drive manufacturers. This paper addresses design methods of surface permanent magnet (SPM) synchronous machines for saliency-tracking self-sensing (position sensorless) position estimation. Machine saliency is created by stator magnetic saturation due to the rotor zigzag leakage flux from surface permanent magnets. Using the machine saliency created by zigzag leakage flux can allow a SPM machine to be suitable for saliency-tracking position estimation without the need of any further special rotor design modification. In addition, another major benefit is achieved, i.e. a saliency role reversal whereby L_d>L_q. This has the advantage of reducing machine cross-saturation and increasing the feasible region for accurate position estimation. All the design procedures are verified by the finite element analysis (FEA), and a 50 W SPM machine prototype is used for performance validation.