Permanent Magnet Synchronous Machine Non-Uniform Demagnetization Detection Using Zero-Sequence Magnetic Field Density

Demagnetization in permanent magnet synchronous machines results in a decrease in the motor average torque and could also increase the torque ripple and consequently vibration and acoustic noise, degrading the overall performance and reliability of the drive. Demagnetization detection can be therefore of tremendous importance. Use of Hall-effect sensors has proven to be a viable option for demagnetization detection. Results reported using this method were based on the analysis of the flux density complex vector; the accuracy of this implementation strongly depends on the angle of the Hall-effect sensor, being also sensitive to implementation issues such as offsets and gain variations of the sensors, magnet temperature, manufacturing tolerances, and stator current injection. This paper proposes the use of the zero-sequence component of the magnetic flux density for demagnetization detection. The use of this signal will improve the accuracy and reduce the sensitivity to implementation issues compared to the use of the flux complex vector.