Line-start permanent magnet motors: proper design for pole-changing starting method

Pole-changing of line-start permanent magnet (LSPM) motors at start-up eliminates all their drawbacks such as poor starting torque, vibration at start-up and synchronisation problems. In addition, by using this method almost all the inherent limitations in the design parameters of line-start motors such as rotor resistance, permanent magnet strength and mechanical stress influenced by pulsating torques are alleviated. Therefore there is no need to compromise between the motor parameters. In this study, the design procedure of these motors is investigated and a high-performance motor based on the pole-changing starting-method is designed and fabricated. Next, the possibility and advantages of replacing laminated cage-bar rotors with solid rotors are investigated for pole-changing LSPM motors. Then, simulations are done by the two-dimensional finite element method and finally, the experimental results are presented. The good agreement between simulation and experimental results validates the theoretical method and also the new design.