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Although cogging torque in magnetic gears (MGs) has been studied, the additional degree of freedom inherent to MGs makes it unclear exactly what is defined as the cogging torque of a MG. Although MGs generally have relatively smooth torque transfer characteristics, this paper reveals that when the gear is used in an up-speed configuration, cogging effects may be amplified under startup conditions. This paper distinguishes between two kinds of cogging torque in MGs, termed the synchronous cogging torque and the true cogging torque. Calculation of the true cogging torque is more difficult than the synchronous cogging torque, but an approximation to the true cogging torque can be obtained using the synchronous cogging torque. The theory is verified experimentally and supported further by results from dynamic simulations. The impact on magnetically geared machines is also considered. [ABSTRACT FROM AUTHOR]

It is well known that the Newton–Raphson method is the most popular iterative method for nonlinear finite element problems. The method has a quadratic convergence. Under certain conditions on the Jacobian of the functional and the initial guess the Newton–Raphson method can converge very fast. However, standard evaluation of such Jacobian may not be possible for the solution of nonlinear hysteresis field problems. This is due to the nature of the magnetization curves that may not be differentiable or possess a very steep gradient. In this paper, an alternative finite element implementation using the Newton–Raphson method for hysteresis field problems is described in detail. To improve the convergence of the method, a method for evaluation of the initial guess is also proposed. It is shown that the Newton method can be reliably used for solving hysteresis field problems. [ABSTRACT FROM PUBLISHER]

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 \,\cdot \,\textm/\textm^\text 3 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

In the past decade, wind power generation has taken center stage in renewable energy development. Currently, the mainstream power-train of a wind turbine system consists of mechanically geared doubly-fed induction generator with a partially rated converter. However, gearbox failures account for the largest amount of downtime, maintenance and loss of power generation. Recently, magnetic gears emerged as an alternative technology to mechanical gears as they offer distinct advantages, such as high torque density, reduced acoustic noise and vibration, lower maintenance and improved reliability, inherent overload protection and contact-less power transfer. In this paper, magnetic gear technologies for wind power applications are investigated in some detail. The distinct merits of magnetic gear technologies are explored together with the challenges associated with this technology for wind energy applications. [ABSTRACT FROM AUTHOR]

In this paper, two design optimisation methods are evaluated using gradient-based optimisation for electric vehicle traction applications. A driving cycle-based approach is used to evaluate specific operational points for the design optimisation procedure. To determine the operational points, an energy centre of gravity (ECG) approach is used. Both optimisation methods are described, namely the point based method and the flux mapping method, with a focus on the flux mapping procedure. Within the flux mapping approach, an inner optimisation loop is defined in order to maintain the stability of gradient calculation for the gradient-based optimisation. An emphasis is placed on the importance of how the optimisation problem is defined, in terms of the objective function and constraints, and how it affects a gradient based optimisation. Based on a design case study conducted in the paper, it is found that the point-based strategy realised motor designs with a slightly lower overall cost (5.66% lower than that of the flux mapping strategy with 8 ECG points), whereas the flux mapping strategy found motor designs with a lower input energy (1.48% lower than that of the point-based strategy with 8 ECG points). This may be attributed to the difference in the definition and interpretation of constraints between these two methods. It is also shown that including more operational points from the driving cycle in the design optimisation leads to designs with reduced total input energy and thus better drive-cycle energy efficiency. This paper further illustrates the significant computational advantages of a gradient-based optimisation over a global optimisation method as it can be completed within a fraction of the time while still finding a global optimum, as long as the problem definition is correctly determined. [ABSTRACT FROM AUTHOR]

In recent years, the permanent magnet vernier machine (PMVM) has attracted much attention in the research community. Many studies have shown that PMVMs possess superior torque density and are suitable for high-torque and low-speed applications. Some of them compared PMVMs with the direct-drive permanent magnet synchronous machines (PMSMs), but these studies focused mainly on sub-kW power levels. There is little work in the literature that conducted the comprehensive evaluation of PMVM technology for more specific applications. This article presents the design optimization of a 15-kW surface-mounted PMVM and its comparison with an equivalent conventional PMSM for wind generator applications. It attempts to objectively weigh the relative merits of the two wind generator systems and outline their respective advantages and disadvantages. For validation purposes, an optimally designed 15-kW PMVM was constructed and experimentally evaluated, which is one of the largest PMVM prototypes ever reported in the literature. It shows that the PMVM can be a competitive alternative to the PMSM for this application. [ABSTRACT FROM AUTHOR]

This paper presents the design, construction, and experimental performance evaluation of an axial flux magnetically geared permanent magnet (MGPM) machine for wind power application. The optimum electromagnetic design for both magnetically coupled and decoupled configurations is described. Considering the complex structure of the axial flux MGPM machine, special attention is also paid to the mechanical design aspects. The optimized results show that a torque density in excess of 100 kNm/m3 could be achieved for the active gear part. The inherent overload protection of the MGPM machine has also been demonstrated. Furthermore, the design-related aspects and issues are analyzed and discussed in detail in an attempt to outline problem areas in the design process. Relevant discussions are given and conclusions are drawn. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]