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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]

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]

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]

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]