Browsing by Author "Gerber, Stiaan"
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- ItemEvaluation and design aspects of magnetic gears and magnetically geared electrical machines(Stellenbosch : Stellenbosch University, 2015-12) Gerber, Stiaan; Wang, R-J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: In the past decade, magnetic gears and magnetically geared electrical machines have emerged as electromechanical devices with exceptionally high torque densities. Their distinct advantages such as low maintenance requirements and overload protection make these devices attractive for many applications. Although significant amount of research has been carried out in this fast-moving field, there are still many design related aspects that have not been thoroughly investigated. This study is concerned with the design optimization and performance evaluation of these devices. An efficient design optimization methodology, specifically aimed at magnetically geared machines (MGMs), is proposed. This design approach allows the components of these integrated machines to be appropriately matched. Challenges associated with the accurate modeling of these special machines, such as the prediction of the impact of end-effects and the high computational cost of simulating movement, are investigated. The proposed design methodology is successfully applied to the design of two different MGMs, of which one features a novel rotor structure. Prototypes based on the designs have been constructed and experimentally evaluated. There is generally a good correlation between the predicted and measured performance results. A method of analyzing the operating points of these machines is also presented. In addition to the two MGMs, a vernier machine, which is based on similar operating principles, is designed, constructed and experimentally evaluated. A detailed comparison of these machines with a more conventional direct-drive permanent magnet machine is conducted in order to assess their respective advantages and disadvantages. The comparison considers small machines with an active stack length of 50mm and an outer diameter of 140 mm. In this fixed-volume comparison, it is found that the MGMs are superior in terms of their torque capability and efficiency. The vernier machine also has a good efficiency and produces the highest torque per volume of magnet material. Based on the merits of MGMs that are demonstrated in this study, further development of these machines is warranted.
- ItemA finite element based optimisation tool for electrical machines(Stellenbosch : University of Stellenbosch, 2011-03) Gerber, Stiaan; Strauss, J. M.; Randewijk, P. J.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Knowledge of the magnetic fields in the domain of electrical machines is required in order to model machines accurately. It is difficult to solve these fields analytically because of the complex geometries of electrical machines and the non-linear characteristics of the materials used to build them. Thus, finite element analysis, which can be used to solve the 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 simple because the performance of the machine has a non-linear dependence on many variables. In these circumstances, numerical optimisation using finite element analysis is the most powerful method of finding optimal designs. In this thesis, the work of improving an existing finite element simulation package, formerly known as the Cambridge package among its users, and the use of this package in the optimisation of electrical machine designs, is presented. The work involved restructuring the original package, expanding its capabilities and coupling it to numerical optimisers. The developed finite element package has been dubbed SEMFEM: the Stellenbosch Electrical Machines Finite Element Method. The Cambridge package employed the air-gap element method, first proposed by Razek et. al. , to solve the magnetic field for different positions of the moving component in a time-stepped finite element simulation. Because many new machine topologies have more 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, the ability to model machines with multiple air-gaps using the air-gap element method was implemented. Many linear electrical machines have tubular, axisymmetric topologies. The functionality to simulate these machines was newly implemented because the original program was not capable of analysing these machines. Amongst other things, this involved the derivation of 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.  and the extension of the method to the Cartesian coordinate system by Wang et. al. [29, 30], completes the derivation 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 simulation and at the level of the optimisation program. The final product is a more powerful, more usable package, geared for the optimisation of electrical machines.