Combined magnetic vector-scalar potential finite element computation of 3D magnetic field and performance of modified Lundell alternators in space station applications.

摘要

A novel method of combined use of magnetic vector potential (MVP) based finite element (FE) formulations and magnetic scalar potential (MSP) based FE formulations for computation of three-dimensional (3D) magnetostatic fields is developed in this dissertation. This combined MVP-MSP 3D-FE method leads to considerable reduction by nearly a factor of 3 in the number of unknowns in comparison to the number of unknowns which must be computed in global MVP based FE solutions. This method allows one to incorporate portions of iron cores sandwiched in between coils (conductors) in current-carrying regions. Thus, it greatly simplifies the geometries of current carrying regions (in comparison with the exclusive MSP based methods) in electric machinery applications. A unique feature of this approach is that the global MSP solution is single valued in nature, that is, no branch cut is needed. A Newton-Raphson procedure with a novel concept of an adaptive relaxation factor was developed and successfully used in solving the 3D-FE problem with magnetic material anisotropy and nonlinearity.; The combined MVP-MSP 3D-FE solution method, in conjunction with the state-space equations using the natural abc-frame of reference, forms a complete computer aided model to analyze and predict machine parameters and performances. This modeling tool was applied to 3D magnetic field analysis and machine performance computations of an example 14.3 kVA modified Lundell alternator. The effects of magnetic material nonlinearity and the space harmonics due to complex magnetic circuit geometries were fully included in the 3D-FE computed machine winding inductances. Results of computed open-circuit, short-circuit, as well as rated load and over-rated load conditions were found to be in excellent agreement with corresponding test values. In addition, a design alteration, in which the stator stack length of the example alternator is stretched in order to increase voltage and volt-ampere rating, were studied. These results demonstrate the inadequacy of some conventional 2D-based design concepts and the imperative of this type of 3D magnetic field modeling in analysis of such MLA class of machines. The modeling technique and algorithm developed in this research can serve as an excellent tool for design optimization and synthesis studies of electric machinery.