Influence of d- and q-axis currents on demagnetization in PM synchronous machines

This paper investigates the influence of d- and q-axis current components on the static demagnetization behavior of permanent magnet (PM) synchronous machines. Finite element (FE) analysis is used to analyze and simulate the behavior of an interior permanent magnet (IPM) machine. The flux density is recorded at several points inside the magnets for various magnitudes of both d- and q-axis current and compared to a threshold value that would result in irreversible demagnetization. Both current components are found to have a significant influence on the demagnetization behavior of the permanent magnets, particularly in the regions that are most at risk for demagnetization. Results show that q-axis current supplied to the machine under some circumstances can offset the degrading effect of d-axis current that would otherwise result in demagnetization. Similar trends are exhibited in IPM machines with both rare-earth and ferrite magnets. Implications of this current component interaction for reducing magnet vulnerability to demagnetization are examined to better understand the opportunities to use it constructively in the design future IPM machines and control strategies with improved electromagnetic robustness.