A finite element based optimisation tool for electrical machines

[摘要] ENGLISH ABSTRACT: Knowledge of the magnetic fields in the domain of electrical machines is required in orderto model machines accurately. It is difficult to solve these fields analytically because ofthe complex geometries of electrical machines and the non-linear characteristics of thematerials used to build them. Thus, finite element analysis, which can be used to solvethe magnetic field accurately, plays an important part in the design of electrical machines.When designing electrical machines, the task of finding an optimal design is not simplebecause the performance of the machine has a non-linear dependence on many variables.In these circumstances, numerical optimisation using finite element analysis is the mostpowerful method of finding optimal designs.In this thesis, the work of improving an existing finite element simulation package, formerlyknown as the Cambridge package among its users, and the use of this package in theoptimisation of electrical machine designs, is presented. The work involved restructuringthe original package, expanding its capabilities and coupling it to numerical optimisers.The developed finite element package has been dubbed SEMFEM: the Stellenbosch ElectricalMachines Finite Element Method.The Cambridge package employed the air-gap element method, first proposed by Razeket. al. [2], to solve the magnetic field for different positions of the moving componentin a time-stepped finite element simulation. Because many new machine topologies havemore than one air-gap, the ability to model machines with multiple air-gaps is important.The Cambridge package was not capable of this, but during the course of this work, theability to model machines with multiple air-gaps using the air-gap element method wasimplemented.Many linear electrical machines have tubular, axisymmetric topologies. The functionalityto simulate these machines was newly implemented because the original program was notcapable of analysing these machines. Amongst other things, this involved the derivationof the coefficients of an axisymmetric air-gap element's stiffness matrix. This derivation,along with the original air-gap element derived by Razek et. al. [2] and the extension ofthe method to the Cartesian coordinate system by Wang et. al. [29, 30], completes thederivation of all two-dimensional air-gap elements. In order to speed the numerical optimisation process, which is computationally expensive,parallelisation was introduced in two areas: at the level of the finite element simulationand at the level of the optimisation program.The final product is a more powerful, more usable package, geared for the optimisationof electrical machines.

[发布机构] Stellenbosch University