Rotor Design of Line-Start Synchronous Reluctance Machine With Round Bars

Within the field of industry applications, the induction machine (IM) is the most used motor type, due to its robustness and line-start ability. However, the need to constrain global warming demands new sustainable technologies with high efficiency. Therefore, line-start synchronous reluctance machines could be an opportunity to achieve a high efficiency for several industry applications, especially for constant-speed drives. This paper introduces a unique rotor design for line-start synchronous reluctance machines (LSSynRMs). Additionally, the influence of the rotor bar material/resistance and the stator resistance in comparison to common IMs for industrial applications is investigated. Finite element method calculations were used for the design and the efficiency enhancement was verified using experiments. Within the context of this analysis, a 4-kW-rated IM with an efficiency rating of IE3 was chosen as a benchmark motor. The new rotor-cage design decreases the motor losses at steady state by about 28%. This promising approach could be used to upgrade IMs in industry environments instead of replacing them. Nevertheless, a challenge in the design is a good balance between the steady-state performance and synchronization capability, which in turn limits the range of industrial applications for highly efficient LSSynRMs.