Analysis and Suppression of Cross-Coupling Demagnetization in Dual Permanent Magnet Machine for Direct-Drive Application

Dual permanent magnet (PM) machines synthesize two PM excitations together and potentially exhibit higher torque density than conventional single-PM excited machines. In dual-PM excited machines, the existence of one PM excitation tends to cause interior flux density reduction and irreversible demagnetization of the other PM set, and this feature is recognized as cross-coupling demagnetization. Therefore, this article systematically analyzed the mechanism and influence of this unique phenomenon in a dual-PM prototype machine. The results reveal that the cross-coupling demagnetization can result in up to 18% torque reduction under a severe working conditions if the machine is not properly designed. Increasing one set of PM thickness along the magnetization direction is beneficial to enhance the self-demagnetization withstanding ability, whereas the cross-coupling demagnetization on the other PM set has deteriorated. In order to eliminate such a side effect, some techniques, e.g., removing the demagnetization region and alleviating the mutual flux path, are presented to suppress the demagnetization. It is revealed that the demagnetization rate can be reduced to less than 3% with proper design. Finally, a dual-PM prototype is manufactured and tested to validate the improvement of demagnetization withstanding capability by using the presented suppression technique.