Effects of toothless stator design on the dynamic performance of permanent magnet generators
Abstract
A comprehensive study on the impact of a toothless stator design on dynamic performance characteristics of high speed permanent magnet (PM) generator-load systems is presented. The study is performed using a computer-aided method which is based on state space models in natural abc frame of reference. The approach is general in nature and includes the effects of magnetic saturation and space harmonics on machine parameters. The approach involves a series of two dimensional nonlinear magnetostatic field solutions in conjunction with energy perturbation method. Based on this approach the machine-load system performance characteristics are predicted under normal and fault conditions. The approach is applied to a 75 kVA, 208 V, 400 Hz, two-pole, PM generator. Two particular stator designs, a toothless and a conventional type stator (with iron teeth), are considered. Using this approach, the effects of toothless design on dynamic model parameters of PM generator are presented. Also, a validation by comparison to experimentally based data is given. Hence, it is demonstrated that the effects of rotor saliency and armature loading on machine parameters are minimized for toothless design. Furthermore, the impact of toothless design on core and stator conductors eddy current losses in PM generator are studied. The method involves a series of magnetic field solutions, which results in radial and tangential flux density components and associated space harmonics throughout the machine cross-section, including stator conductor regions. The conductor eddy current and core losses are estimated and compared for both designs. Furthermore, the results of a study on the effect of conductor size on the stator conductor eddy current loss are given. Accordingly, it demonstrated that the sum of conductor eddy current and core losses in toothless design can be at a lower level than that encountered in conventional design. In addition, the computer-aided modeling approach is used to analyze and predict the dynamic performance of PM generator when feeding ac and dc rectified loads. Based on above, it is demonstrated that toothless design could result in lower levels of harmonics in the delivered power to the load. Also, it is shown that toothless design results in lower power levels compared to conventional design. Accordingly, an extruded toothless design is studied and it is shown that output power level can be boosted by increasing the axial length of machine while maintaining lower level of harmonics.
This paper has been withdrawn.