Line-Start PM-Assisted Synchronous Motor Design, Optimization, and Tests

Line-start synchronous motors (LSSMs) have been recently introduced in the motor market to meet the new efficiency class requirements. They exhibit high efficiency and power factor compared with induction motors (IMs), but the complex design, manufacture, and high cost due to presence of permanent magnets (PM) limit their widespread use. This paper proposes a new approach for the design of LSSMs, in which an important torque contribution is given by the reluctance torque component. Both steady-state and dynamic capabilities are considered. A stochastic optimization is used to determine the parameters that maximize the synchronous torque. The possibility to apply the recent improvements on the synchronous reluctance machine design to LSSMs is discussed. Experimental measurements are carried out on an LSSM prototype achieved from the optimization. The results are compared with the predictions. Two different PM volumes are tested in the same rotor structure, evaluating their impact on motor performance. From the experimental tests, an overview comparison between the IM and LSSM performance is given.