Analytic modelling and dynamic analysis of pole-changing line-start permanent-magnet motors

Pole-changing of line-start permanent magnet motors at start-up has many advantages and improves starting torque, synchronisation capability and steady-state performance. However, some oscillations may occur after switching which may cause dynamic problems. Depending on the speed and torque angle at switching time, the magnitude of oscillations may be large and even may lead to instability and reoccurrence of the sub-synchronous mode. In this study an analytic modelling is implemented to analyse the dynamic performance of motor with pole-changing method and the results have been verified by the 2-D finite-element method. In the analysis the various impacts of parameters such as switching speed, torque angle, inertia and load torque on the synchronisation capability are investigated. Next, two solutions are presented that overcome the stochastic dynamic problems and cause a suitable synchronisation. Finally, the experimental results are presented to verify the validity of the proposed methods and the overcoming of the dynamic problems.