This paper presents a literature review on magnetic gears, highlighting the advantages of using these technologies for mechanical power transmission applications in wind energy conversion systems and transportation, such as in electric vehicles. Magnetic gear technologies have important advantages over their mechanical counterparts. They can perform the speed change and torque transmission between input and output shafts by a contactless mechanism with a quiet operation and overload protection without the issues associated with conventional mechanical gears. The paper describes the fundamentals and operating principle of the field-modulated magnetic gear topologies and investigates the magnetic torque transmission mechanism. However, despite all the advantages highlighted in different research and development reports, there is still no convincing evidence to show that magnetic gear technologies are an acceptable alternative for industrial applications. The aim of this paper is to summarize previous work on magnetic gears to identify the topologies most suited for mechanical power transmission systems in wind energy conversion systems and electric vehicle applications. These applications will show that research and development of magnetic gear technologies contribute significantly to solutions for sustainable systems, a subject to which our current civilization must pay a lot of attention.

In this article, the parameter identification of a brushless DC motor (BLDC) is presented. The approach here presented is based on a direct identification considering a three-phase line-to-line voltage electromagnetic torque as function of the electric currents and rotor speed. The estimation is divided into two stages. First, the electrical parameters are estimated by well-known no-load and DC tests. Consequently, estimation of mechanical parameters is performed using a recursive Least Square Algorithm. The proposed approach is validated by comparing model responses to motor real time responses. Additionally, the design, digital simulation and real time implementation of a PI rotor speed controller, based on the estimated model, validate the identification proposal presented here.

This paper presents a new and rigorous analytical calculation of electromagnetic field and eddy current losses in the zones of transformer tanks where bushings are mounted. This is done by solving Maxwell's equations in the regions surrounding bushings, with the corresponding boundary conditions and considering linear permeability. Then, by solving the modified Bessel's equation, the analytical formulas to calculate the magnetic field and eddy current losses in these regions are obtained and several cases are studied. The results are compared with 3-D finite element simulations and show very close correspondence. The obtained formulas allow straightforward calculations that can help designers to select proper parameters to optimize the design of transformers. This paper can be taken as the basis for the analysis of the nonlinear permeability case.

Successful analytical formulas have been previously proposed to calculate the losses in tank regions of transformers assuming linear permeabilities in the analyzed boundary-valued problem. This has resulted in easy-to-implement and low-cost computational design procedures from a transformer factory economical point of view. However, designers and analysts of transformers are constantly seeking new ways of reducing transformer losses in actual power networks with thousands of transformers. As a result, this paper has focused on proposing new analytical formulas to determine the electromagnetic field in bushing regions of transformers, taking account of the true nature of the nonlinear permeability behavior of the tank wall. This way, the nonlinear Maxwell's equations in the regions surrounding the bushings are solved using an integral equation formulation that properly includes boundary conditions. A practical iterative procedure is thus proposed to solve the resulting nonlinear equation. The iterative scheme shows excellent numerical convergence properties with a very low computational demand as compared with finite-element (FE) nonlinear models. A comparison between our analytical results and those of 3-D FE simulations reveals a close match for a wide range of conductor currents. Hence, our new formulas can be used to improve the design of transformers, increasing their efficiency.

Existing circuit-field coupling schemes can deal with a single magnetic field model connected to an external circuit. However, modern electrical systems are a complex interconnection of multiple magnetic devices, which opens up the question of how to consider multiple interacting field models. In this paper, we propose a scheme based on the finite element and modified nodal analyses, to solve the problem of coupling multiple magnetic field systems with circuit networks. The proposed methodology is systematic since each element within the electrically connected problem has a building block, which is easily inserted into the global system of equations. This applies to any magnetic field system, where massive and filamentary conductors are equally accommodated. Hence, each electrical network component can be modeled with any desired level of detail: as a magnetic system (distributed parameter model) or as a circuit (lumped parameter model). To show the flexibility and power of the proposed methodology, the finite-element models of a three-phase induction motor and a transformer are electrically interconnected through circuits that represent an infinite bus bar and a short transmission line.

A strong circuit-field coupling technique that can analyze multiple magnetic field systems (2D Cartesian and axisymmetric) is adapted to study power transformers. The technique is based on finite-element (FE) and modified nodal analyzes, leading to a multi-field system approach than can effectively take account of the 3D magnetic field existing inside and outside the transformer core. Hence, cumbersome 3D FE simulations are circumvented, overcoming high computational costs. A 2D Cartesian FE model is set up to represent the cross-section of the transformer core and its three-phase winding, whereas an axisymmetric representation is employed for the end sections of each set of windings (one per phase). All models and their associated circuit systems are simultaneously solved, providing a circuit-field method that is easy to implement at low computational cost, keeping the well-known advantages of 2D FE modeling. Electrical currents and local values of magnetic flux density are calculated for two limiting conditions: rated-load and short-circuit operation. Our approach shows a remarkable small difference (no higher than 1%) with a full 3D FE model.