###### Abstract  
Permanent magnet-assisted synchronous reluctance motors (PMA-SynRMs) are widely used in various fields due to their significant advantages, including strong torque output, high efficiency, excellent speed regulation, and low cost. The PMA-SynRM with asymmetric-rotor structure has a weaker anti-demagnetization performance than the conventional PMA-SynRM due to its multi-layer and thin permanent magnets construction. According to the finite element (FEM) simulation analysis, the anti-demagnetization performance of the asymmetric-rotor PMA-SynRM can be improved by adding bypass magnetic bridges on the ribs of the flux barriers and by changing the positions of the permanent magnets. The rotor structure of the proposed model is globally optimized by combining the two methods. Anti-demagnetization performance is improved as much as possible under the premise of ensuring the torque performance of the basic model. After multi-objective optimization, there is almost no difference between the optimized model and the basic model in terms of no-load air-gap flux density, no-load Back-electromotive force (EMF), and average torque. The maximum demagnetization rate of the optimized model is reduced by 81.44% compared with the basic model, and the anti-demagnetization performance is significantly improved. At the same time, the torque ripple is also reduced by 44.14%, which is obviously reduced. Compared with the basic model, the optimized model has better stability and reliability. PMA-SynRM; asymmetric-rotor; bypass magnetic bridge; anti-demagnetization; multi-objective optimization +
Footnote †: journal: Applied sciences  
Currently, the studies on anti-demagnetization performance of PMA-SynRM mainly focus on the design of the flux barrier structure, permanent magnets, and magnetic circuits. One study [22] investigated the flux density distribution at each position/layer on the permanent magnet. The risk of demagnetization was also assessed by obtaining the working point of the permanent magnet based on the variation of the excitation current, current phase angle, and temperature. The results of the analysis showed that a high current phase angle coupled with the effect of high temperature was the main cause of demagnetization of the permanent magnet. Another study [23] mentioned that the width and thickness of the permanent magnet should be increased to reduce the risk of demagnetization in PMA-SynRMs. An analytical method is also proposed, where the width and thickness of the permanent magnets could be calculated based on the given air-gap flux density and the stress of the permanent magnets themselves. Such an approach improved the anti-demagnetization performance of the PMA-SynRM, but also increased the cost of the permanent magnet. One study [24] comparatively analyzed the demagnetization under different number of layers of flux barrier, permanent magnet combinations, and number of poles. The results showed that the two-layer flux barrier and the eight-pole design had lower risk of demagnetization. In another study [25], it was shown that under continuous loading and demagnetization conditions, small and medium sized machines were more resistant to demagnetization compared to large machines and had scope for transient overloads. A subsequent study [26] pointed out that by introducing the bypass magnetic bridges at the end of the flux barriers, it was possible to allow part of the armature magnetic field to pass through the bypass magnetic bridges, reducing the demagnetization effect on the permanent magnets. Simulation results showed that this bypass magnetic bridge structure significantly improved the anti-demagnetization performance of the motor. A study [27] compared the anti-demagnetization performance of ferrite assisted synchronous reluctance motors with centralized and distributed windings and found that the distributed windings were able to provide stronger anti-demagnetization performance.