Design of permanent magnets to guarantee frequency-changing startup for PM synchronous machines

The permanent-magnet synchronous machine (PMSM) is becoming more and more attractive for both industrial and electric vehicle applications because of its inherent advantages of high power density and high efficiency. However, the PMSM is not self-starting. Apart from inserting additional cage windings in the rotor, the most common starting method is to gradually increase the applied frequency by using a frequency-changing inverter. Nevertheless, due to the nonlinear dynamics of the PMSM, this frequency-changing startup may be failure or exhibit chaotic behaviors. In this paper, the nonlinear relationship between the sizing of PMs and the startup behaviors of PMSMs was investigated. Both computer simulation and experimental results were given to support the design criterion.