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The slot opening function, also called relative air gap permeance, is a function which, multiplied by the flux density distribution of a slotless geometry, gives the flux density distribution of a slotted configuration. Here, the magnetic field inside the air gap of a multi-slot surface facing a smooth one was studied, by solving the Laplace equation inside the air gap, in terms of a Fourier series. To obtain the Fourier coefficients, at first, the conformal mapping analytical solution of a single-slot configuration along the smooth surface, was considered. Then, the principle of superposition of the single-slot lost flux density distributions was applied to obtain the multi-slot distribution. The approach is valid in general, and in the case of interference among the flux density distributions of adjacent slots, where their mutual effect cannot be neglected. The field distributions obtained by using the proposed slot opening functions were compared with FEM simulations, showing satisfactory agreement. The numerical accuracy limits were also analysed and discussed. [ABSTRACT FROM AUTHOR]

This paper presents an analytical study of the air-gap magnetic field of a surface permanent magnet (SPM) linear, slot-less machine with a Halbach PM configuration, under the no-load condition. While other analytical formulations of the magnetic field generated by PMs are available, they exhibit some drawbacks, such as only providing a Fourier series, or being suitable to determine magnetic field average values, but not local magnetic field distributions. On the contrary, the proposed approach allows the determination of a unique, closed-form formulation for the slot-less machine air-gap field. This is obtained starting from the complex expression of the magnetic field of a conductor, inside the air gap, between two parallel smooth iron surfaces, obtained by means of the method of images. The magnetic field due to an infinitesimal conductor belonging to a current sheet is then integrated along a segment, providing the expression of the magnetic field due to the corresponding linear current density distribution, for current sheets perpendicular or parallel to the iron surfaces. Any Halbach PM segment disposition can, hence, be obtained via a suitable combination of field distributions generated by couples of current sheets with perpendicular and parallel orientation. Lastly, the no-load magnetic field expression with a Halbach array of PMs is retrieved. The proposed analytical model provides an accurate representation of the magnetic field distribution produced by any Halbach array, with an arbitrary number of segments and orientations. Additionally, the results obtained from the proposed analytical expressions are compared with FEM simulations realized by commercial software, and show an excellent agreement. [ABSTRACT FROM AUTHOR]

The following paper presents an analytical study of the air-gap magnetic field distribution produced by the armature reaction of a linear machine. Based on the method of images, the magnetic field generated by a current carrying conductor inside the air-gap between two smooth infinitely permeable iron surfaces is modeled as a complex 2D function. The conductor model then becomes a current sheet model and horizontally oriented current sheets are used to model the magnetic field produced by the armature reaction for smooth ferromagnetic surfaces. Focus will be given to the study of the slot opening function in front of energized slots in comparison to the not energized ones of the classical theory pointing out some remarkable differences. Later, the model is extended to slotted geometries using a complex slotting function adapted for energized slots. At last, the Maxwell tensor expressed in complex formulation will be integrated to obtain the force components acting on the machine tooth tips, quantities that will be compared with FEM simulations in order to validate the proposed analytical model. [ABSTRACT FROM AUTHOR]

This paper presents an analytical study of the air-gap magnetic field of a Surface Permanent Magnet (SPM) linear machine under no load. By means of the method of images, the complex expression of the magnetic field of a conductor, inside the air gap between two smooth iron surfaces, is retrieved. Then, integrating the conductor expression, the formulation of the magnetic field of a current sheet and thus the one of a SPM, using two vertical current sheets, is obtained. At last, the no-load magnetic field expression, for a generic time instant, of a slotless machine is retrieved. The novelty of the proposed approach is the availability, due to a different calculation approach, of a unique closed-form formulation for the slotless machine air-gap field, a quantity that, in literature, is usually present in Fourier series formulation. Additionally, as a means to calculate integral quantities and show the goodness of the method a complex slotting function is introduced to account for the slotted geometry. Finally, starting from Lorenz's force formulation, the expression of the Maxwell tensor in complex form is retrieved and the contribution of forces, integral of the complex stress tensor quantity, will be calculated and compared with FEM simulations, showing a good agreement also with the analytical slotted model. [ABSTRACT FROM AUTHOR]

In this paper, an analytical approach is proposed in developing a lumped parameter thermal model for the stator coils of naturally cooled axial-flux tooth-coil permanent magnet machines. The model comprises one tooth, the coil around it, and the air channels between coils and the teeth supporting structure; each component is subdivided into cuboidal or arc subelements. An expression of the convective exchange coefficient is proposed to take into account the radial position of each tooth. Experimental results validate the proposed model, which can also be used in the design stage of a machine. [ABSTRACT FROM AUTHOR]

This paper evaluates the parasitic currents that can occur in the structural part of some types of yokeless and segmented armature axial flux permanent magnet machines, where the frame-supporting stator floating teeth can originate stray paths. In this paper, these paths are defined and modeled, and the consequent effects (induced electro motive forces and currents) are estimated. The amount of these effects depends on the machine geometry, the magnetic circuit structure, and the winding layout. In this paper, the analysis is performed on two different rating machines, comparing their results. The model is validated by measurements on the corresponding prototypes. [ABSTRACT FROM AUTHOR]

In some topologies of yokeless and segmented armature (YASA) axial flux permanent-magnet (AFPM) machines, the particular frame structure required to fasten floating teeth can originate stray paths where parasitic currents may circulate. This paper investigates how the amplitude of these currents and the related additional Joule losses depend on the machine size. Reference is made to wind energy generators, rated from some tens of kilowatts up to a few megawatts. The developed model is mainly based on wind turbine basic data of vendor data sheets, and on the quantities evaluated and tested in two YASA AFPM prototypes, rated 50 and 200 kW. [ABSTRACT FROM PUBLISHER]

This paper analyzes some operational issues of three-phase surface-mounted permanent magnet synchronous generators (PMSGs) connected to a diode rectifier. This simple configuration coupled to a single-switch dc–dc converter is used in small-scale wind energy conversion systems, as well as in energy harvesting systems, to reduce costs. The diode rectifier causes an intrinsic limit for the maximum convertible power, which is related to the load impedance matching, and additional joule losses due to the distorted currents. By using an analytical steady-state model of the rectifier and of the PMSG, this paper discusses how to achieve two particularly meaningful operating conditions characterized respectively by the maximum power transfer and the maximum power per ampere. The theory is validated by simulation and test results on a prototype. [ABSTRACT FROM AUTHOR]

Due to the high torque capability, axial flux (AF) permanent-magnet (PM) machines are an interesting solution for direct driven wind energy conversion systems and low-speed motors. However, the structure of such machines makes them sensitive to geometrical imperfections due to manufacturing process. This paper analyzes the effects that various types of geometrical imperfections produce in concentrated coil AF PM generators. In particular, a case study is presented, where the mechanical stresses, the resulting axial force, and the bending torques on the shaft, as well as the circulation current in the winding parallel paths, are calculated. The results obtained by means of an analytical approach are compared with those based on finite element method simulations and are validated by some experimental results on a prototype. [ABSTRACT FROM PUBLISHER]

Electrical machines are generating and using most of the electrical energy converted worldwide from fossil fuels or renewable sources. An optimized electrical machine means not only less input energy used but also higher electromechanical energy available as output. This is translated into getting more with less and having an impact on the total amount of greenhouse gases released into the atmosphere, thus mitigating global warming. Benefiting from the latest developments in the electrical machine field are various industries such as electric propulsion [new electric vehicles (EVs) and plug-in hybrid EVs (HEVs)], renewable energy harvesting, consumer applications, and military and aerospace products. This article brings together the contributions from several authors working in academia and industrial research and development centers and comprises a collection of short analyses dedicated to the hottest topics in the electrical machine research community. The article focuses on special and difficult problems to be solved in the design process of the most important electrical machine topologies. The topics discussed cover new machine topologies such as fractional slot winding motors and synchronous reluctance motors; electromagnetic, mechanical, and thermal problems in permanent magnet (PM) machines design; operation of high-speed machines and high-power turbo generators; noise and vibration reduction in switched reluctance motors (SRMs) for automotive applications; high-efficiency induction machines (IMs) configurations compatible with the new international standard and a comprehensive analysis of universal motors (UMs). [ABSTRACT FROM PUBLISHER]

An analytical method is presented to evaluate the field and global quantities for the operation and design analysis of axial flux permanent-magnet (PM) machines. The method, of general applicability, is based on the definition and superposition of suited field functions, able to accurately model the different singularities of the studied device: PM field distribution, effects of slotting, and radial end effects. Selected explorative FEM analyses are used in order to investigate the field functions shape and to help in identifying their structure and parameters. Then, the flux density distribution is obtained, as a function of the rotor position, taking into account some manufacture dissymmetry effects, such as air-gap offsets and PM rotor disk inclinations. This approach allows to analyze the effect of dissymmetry on the circulation of current among winding parallel paths in no-load operation. Moreover, by using the Maxwell stress tensor, the stress distribution is evaluated, as well as the resultant axial forces and the bending torques on the shaft due to the rotor disk tilts. Several FEM simulations show the soundness of the proposed method, which exhibits high accuracy and great evaluation speed. [ABSTRACT FROM PUBLISHER]

This paper deals with the ac–dc interface conversion in grid-connected wind energy conversion systems based on modular permanent-magnet synchronous generators. In particular, some solutions based on diode rectifiers are extensively analyzed as for the waveforms, the efficiency, and the torque ripple, by considering several connections, which are allowed by the inherent modularity of the considered generators. Rectifier schemes with a high number of pulses can be easily realized without using special shifter transformers so that these solutions can be attractive for low- and medium-power applications. [ABSTRACT FROM PUBLISHER]

Some design and operation aspects of axial flux permanent magnet synchronous machines, wound with concentrated coils, are presented. Due to their high number of poles, compactness, and excellent waveform quality and efficiency, these machines show satisfactory operation at low speeds, both as direct drive generators and as motors. In this paper, after a general analysis of the model and design features of this kind of machine, the attention is focused on wind power generation: The main sizing equations are defined, and the most relevant figures of merit are examined by means of a suitable parametric analysis. Some experimental results obtained by testing a three-phase, 50-kW, and 70-rpm prototype are presented and discussed, validating the modeling theory and the design procedure. [ABSTRACT FROM AUTHOR]

Some electromagnetic and thermal aspects concerning special permanent magnet machines, employed in damping seismic oscillations in structural systems, are examined. The power generated by the machine during a seismic event is regulated by a suited converter and delivered to an external resistor. Some modeling features and selected simulations are examined, together with test results obtained by a prototype. Some special tests, aimed to identify the thermal parameters of the machines, are presented and discussed. [ABSTRACT FROM AUTHOR]

An equivalent circuit of universal motors is developed, based on the design data. After representing the magnetomotive force distribution in the air gap, an analytical expression of the flux linkage of the armature winding coils is derived; this allows for the determination of the expressions of the speed and transformer EMFs induced in the armature winding and theft representation by means of circuit parameters, as a function of the magnetic core saturation. The motor performances are computed, using the circuit parameters determined both analytically (by the design data) and by measurements. Some quantifies are also compared with the ones obtained by finite-element analyses. Finally, the model is validated by experimental tests. [ABSTRACT FROM AUTHOR]