Stiaan Gerber

Design and Evaluation of a Magnetically Geared PM Machine

This paper presents the design and evaluation of a magnetically geared permanent magnet (PM) machine with an inner stator. A brief overview of relevant operating principles is given first. A simplified design and simulation methodology, which can ensure that the magnetic gear and the stator are well matched, is then devised. The method is applied to the design optimization of a small machine resulting in a design with a maximum torque density of 115 kN · m/m3 per active volume. To validate the design, a working prototype has been built and experimentally evaluated. It shows that this computationally efficient design methodology is well suited for the optimization of magnetically geared PM machines. Finally, a method of analyzing the operating points of the machine is described. Relevant conclusions are drawn and recommendations for future work are given.

Asymmetric Flux Barrier and Skew Design Optimization of Reluctance Synchronous Machines

In this paper, an investigation into an alternative topology for reluctance synchronous machine rotor flux barriers is presented. The investigated topology employs a high number of flux barrier variables with an alternative asymmetric rotor structure. The focus in this paper is on maximizing average torque and minimizing torque ripple, using finite element-based design optimization, in order to study the possibility of achieving acceptably low torque ripple. A subsequent investigation into the effect of rotor skew on the proposed optimized design to reduce torque ripple even further is also conducted, as well as the manufacturing and testing of the proposed flux barrier prototype.

Magnetic gear technologies: A review

This paper reviews the historic and current development of magnetic gear technologies. There has been considerable amount of research and development activities on magnetic gear technologies in recent years. However, it is still not clear if this technology is ready for potential industry applications. The purpose of this paper is to summarize the historic and current development work of magnetic gear technologies in an attempt to give readers some insight into the advantages and disadvantages, challenges, opportunities and technology readiness.

Torque capability comparison of two magnetically geared PM machine topologies

This paper presents a comparison of the torque capability of two PM machines with integrated magnetic gears for low speed, high torque applications. The machines are also compared against a more conventional fractional-slot PM machine to evaluate the benefits of the geared machines. The comparison is based on the optimal torque per active mass that could be achieved within a given volume. The machines are optimized using 2D finite element (FE) analysis and the optimal designs are further evaluated using 3D FE analysis. For the geared machines, an optimization procedure is employed which ensures that the gear and stator parts are well matched.

Analysis of the end-effects in magnetic gears and magnetically geared machines

Magnetic gears and integrated magnetically geared machines have recently received much attention due to their exceptionally high torque densities. As in the design and analysis of conventional electrical machines, the finite element method (FEM) has been widely used for this class of electrical machine. For the sake of computational efficiency, the standard practice in FEM modeling is to reduce the problem complexity by applying only two-dimensional (2D) modeling and exploiting periodicity, if any. However, it has been shown by many researchers that there exists a significant discrepancy between the results from two-dimensional and three-dimensional (3D) FEM for these machines. Whilst it is generally believed that this discrepancy is due to severe end-effects, there has been no published work specifically looking into the end-effect mechanisms at work in these machines. This paper attempts to identify the origins of these end-effects and explain why they can be especially significant in magnetic gears and magnetically geared machines. The effect of some critical design parameters on the stall torque is investigated by using both 2D and 3D FEM. Special attention is given to the difference between 2D and 3D results, which helps to establish whether or to what extent 2D FEM can be utilized for the design analysis of these special machines. The impact that end-effects have on the stator load factor, a useful concept in the design of magnetically geared machines, is also investigated.

Evaluation of a prototype magnetic gear

In this paper, the design of a prototype concentric-type magnetic gear is evaluated. The effects that the mechanical bridges connecting the modulator segments have on the performance of the gear have been analyzed by using detailed two-dimensional (2D) finite element (FE) analysis. The magnetic gear suffers significantly from end-effects, which result in a considerable decrease in the peak torque capability as well as excessive losses under high-speed operation. Three-dimensional (3D) FE analysis is employed to identify the origin of the undesired end-effects and to determine which structural components have the greatest negative impact. Insight is then gained into how the prototype could be modified to reduce these end-effects.

Design and evaluation of a PM vernier machine

This paper presents the design optimization and performance evaluation of an outer-rotor vernier machine with surface mounted permanent magnets. First the design specifications of the machine are described, then the design strategy and the optimization procedure are given in detail. A prototype based on the optimum design is manufactured and experimentally evaluated. The measured performances compare favourably with the predicted ones. In addition, a comparison with a more conventional PM machine with non-overlap windings is presented. It shows that, despite the disadvantage of low power factor at high torque, vernier machines can be a competitive alternative to conventional PM machines in some applications.

Flux barrier and skew design optimisation of reluctance synchronous machines

In this paper an investigation into an alternative reluctance synchronous machine rotor flux barrier topology creation technique is presented. The technique investigated implements a high number of flux barrier variables with an alternative asymmetric rotor structure topology in combination with optimisation and finite element analysis. The investigation focuses on maximising average torque and minimising torque ripple in order to study the possibility of achieving acceptable torque ripple machine parameters without implementing rotor skew as torque ripple reduction technique. A further investigation into the effect of rotor skew on the proposed topology is conducted followed by the manufacturing of the proposed flux barrier prototype and testing.

Optimal Design of an Outer-Stator Magnetically Geared Permanent Magnet Machine

In this paper, a magnetically geared permanent magnet (MGPM) machine is proposed for the use in wind power generation. The structure layout, operating principles, and equivalent circuit of the MGPM machine are first described. Then, an efficient finite-element-method-based design optimization approach is formulated and implemented in the design of the machine. The optimized machine shows that a rated torque density close to 70 kNm/m3 can be achieved, which is significantly higher than that of the conventional electrical machines. Furthermore, a prototype machine based on the design is constructed and experimentally evaluated. The measured torque performance shows good agreement with the predicted one, but a significant difference exists between the measured and calculated efficiencies. This is mainly due to higher than the expected mechanical losses in the MGPM machine. Relevant conclusions are drawn based on the analysis of presented results and some key design-related aspects.

Evaluation of Movement Facilitating Techniques for Finite Element Analysis of Magnetically Geared Electrical Machines

The simulation of magnetically geared electrical machines using the finite element method is an especially demanding task when movement has to be considered. Several methods that facilitate movement exist. In this paper, two of these methods, the macro air-gap element (AGE) and the moving band (MB) are applied in a time-stepped static simulation of a magnetically geared machine (MGM). The methods are evaluated in terms of accuracy and computational efficiency, vitally important factors for numerical optimization. The implementation of both methods exploit the multi-core architecture of modern CPUs to solve several steps in parallel, drastically reducing the simulation time. Nevertheless, the computational cost of the AGE is prohibitively high in the simulation of MGMs. The MB is computationally efficient and good accuracy can be achieved using a multilayer approach.