Analysis of High-Speed Permanent Magnet Machines

High-speed permanent magnet machines (HSPMM) are a competent candidate for high-speed applications due to its better efficiency, power factor, and utilization factor in comparison to other types of high-speed electrical machines. In this thesis, both the electromagnetic and mechanical issues of HSPMM including rotor split ratio optimization, rotor stress analysis, and parasitic effects such as rotor eddy current loss and UMF are investigated elaborately by means of analytical and finite element analyses, together with experimental validation.
Firstly, the optimal rotor split ratio of HSPMM is investigated analytically with consideration of stator iron loss as well as rotor mechanical stress. The influence of design parameters such as air gap length and rotor pole pairs on the optimal split ratio is investigated. Both analytical and finite element analyses reveal that the optimal split ratio for HSPMM will be significantly reduced when stator iron loss and mechanical constraints are taken into consideration.
Secondly, the rotor eddy current loss of the four-pole HSPMM with alternate stator winding configuration is investigated. The contribution of each harmonic in the production of magnet loss, either from PM field or armature field, is determined by the proposed method with consideration of stator slotting effect. In addition, the armature reaction induced magnet losses with different stator winding configurations are compared as well. It is found that the value of magnet loss is dependent on both the penetration depth and the amplitude of asynchronous spatial harmonic, which are determined by the specific slot and pole number combination.
Following from this, the existence criterion of UMF in PM machines with odd number stator slot is determined. In addition, the influence of slot and pole number combination on the rotor UMF is investigated.
Finally, a novel HSPMM design methodology considering both electromagnetic and mechanical issues is illustrated. The rotor stress is firstly analysed with consideration of PM segmentation effect. The corresponding worst operating scenarios and influential factors are then investigated. Based on the stress analysis of the HSPMM, the mechanical stress limitation is incorporated as the geometric constraints in the electromagnetic design so that the mutual influence of two different design aspects can be considered.