I. Introduction
With the ever increasing global warming concerns, due to the electric motors have occupied relatively larger portions (∼50%) in total electricity consumptions and mass volumes in industrial and commercial applications, effectively improvements of their efficiencies and thus reduce the equivalent carbon-dioxide emissions have become the main issues in the motor manufacturing industries. Consequently, with comparatively larger output torques, more rigorous operational specifications and energy performance standards about the motor efficiencies have now been enforced for the related applications and market requirements. Based on the corresponding International Electrotechnical Commission 60034 standards [1], it can be seen that to achieve the desired super-(IE4) or even ultrapremium (IE5) classes for those common line-start alternative current (ac) motors [2], [3], proper insertions of the permanent magnets (PMs) into the motor structures are the general solutions. However, no matter it is for new motor installation or for upgrading the existing one, such ac motor will incur higher construction efforts and costs due to those rare-earth PMs. To supply a structural cost-effective scheme, by removing the rotor conductors while maintaining the same stator structures, the synchronous reluctance motor (SynRM) [4] presents a potential alternative for upgrading those applications that the small-power induction motors were commonly applied. Whereas at the tradeoff, the SynRMs are generally operated at comparably lower power factors than those of the induction motors, and more involved driver controls are generally required for the system operations [5]. Nevertheless, along with the fast advance in power electronics technologies, for supplying servo-controlled driven forces on metal and related heavy industries [6], only small portion of the system overall installation costs will be taken up due to such additional driver circuits.