New compositions of Nd-Fe-B powders were produced via gas atomization. Helium and argon were used as atomizing gases. For the same process parameters, helium resulted in a powder that is 6 times finer than the powder produced with argon. In both cases, the atomization conditions were set to achieve fine powders and, therefore, fine microstructures, since this is critical to obtain a suitable coercivity. The powders were sieved to separate the fraction below 20 mu m(similar to 90 % of powder atomized with He). The microstructure is formed by a mix of elongated and equiaxial grains with random crystallographic orientation and an average grain size of similar to 1 mu m, which was measured by Electron Backscattered Diffraction. This kind of measurements and images were taken for the first time for fine helium atomized Nd-Fe-B powders. The embedding of the powder in copper was found to be useful, as the conventional mounting in metallographic conductive resin produced charging of the sample. Annealing up to 1000 degrees C did not cause any significant grain growth that could deteriorate the magnetic properties. Annealing at 700 degrees C for 15 min improved the magnetic properties due to the crystallization of residual amorphous phase. Warm compaction was used to produce magnets with a high volume fraction of magnetic powder (>70 %) and low real porosity (similar to 5 %). These magnets exhibit a high remanence (similar to 0.5 T) and maximum energy product (similar to 35 kJ/m(3)), combined with a suitable intrinsic coercivity (>500 kA/m). The new compositions and processing route could cover a market niche. The thoroughly analyzed powders could be also suitable for some additive manufacturing technologies that require spherical powders with very specific particle size distributions. (c) 2023 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Losses created by skin and proximity effects can be significant in medium to high-speed ac machine designs. These have been extensively studied for form wound coil machines, but regarding randomly-placed round-wire windings, bundle-level proximity losses have been either neglected, computed via finite element (FE) simulations or estimated analytically by methods that require to know the location of each strand within the slot. This article presents a practical, yet accurate method to estimate bundle-level proximity losses in random-wound ac machines without having to specify the location of each individual conductor. The method consists on approximating the turn size and the arrangement of the conductors within the slot from the overall dimensions of the slot and the winding via simple expressions. This procedure is successfully validated via FE simulations and by constructing and experimentally testing two Interior Permanent Magnet Synchronous Machine prototypes with different winding characteristics.

In the last few years, the reduction of the dependency on rare-earth magnets has been one of the main concerns for electrical machine manufacturers. Synchronous reluctance machines (SynRMs) and ferrite permanent magnet-assisted synchronous reluctance machines (PMa-SynRMs) are emerging as alternatives to permanent magnet synchronous machines (PMSMs) in several applications. In low-speed high-torque applications, PMSMs with large amounts of rare-earth magnets are commonly employed. Thus, it is of particular interest to replace PMSMs by SynRMs or PMa-SynRMs. This article studies the feasibility of using SynRMs and ferrite PMa-SynRMs for a direct-drive elevator system. The challenge lies in obtaining performance characteristics comparable to those of PMSMs, but without resorting to the use of rare-earth permanent magnets. The main criteria for designing SynRMs and PMa-SynRMs for low-speed high-torque applications are presented. Afterwards, a SynRM and a ferrite PMa-SynRM are designed for 160 rpm 200 Nm rated conditions, and a performance and cost comparison between these machines and a commercial PMSM is conducted.

It is well known that multiphase machines exhibit the better performance (efficiency, torque density, fault tolerance, etc.) than three-phase machines. From the manufacturing point of view, it is interesting to have the possibility of improving a machine design by just conducting minor changes in the production process. In this regard, six-phase machines emerge as the natural choice to improve a design without modifying the active parts. This article presents an optimal procedure to shift from a three-phase to a six-phase induction motor design by just rearranging the coil connections. By starting from a three-phase winding design, different six-phase winding arrangements are analyzed. A methodology to define all the possible six-phase winding arrangements is presented. Discard criteria based on balanced radial forces and impedances are defined. Afterward, selected winding candidates are compared in terms of analytical calculations and later on, based on finite element (FE) simulations for a 690 V, 1-MW induction machine design. Different possible configurations are evaluated in terms of stator Joule losses, torque ripple, power factor, and electromagnetic efficiency both under healthy and faulted inverter conditions. Finally, a six-phase machine prototype is tested in order to verify the improvement in machine characteristics, thus validating the proposed method.

This study presents the electromagnetic, thermal and mechanical analysis of a 750 kW, 1200 rpm, 690 V surface permanent magnet motor aimed at marine propulsion (azimuth thruster). Based on a preliminary machine design, key electromagnetic design aspects including magnet demagnetisation and magnet loss reduction by tangential and axial segmentation are assessed. Then, three different cooling solutions are evaluated via computational fluid dynamics simulations combining the use of a water-jacket surrounding the stator, wafters attached to the rotor structure and the addition of an inner fan. Subsequently, the dynamic design analysis method is applied in order to check the machine's response to shock loadings due to underwater explosions. Finally, a machine prototype is successfully manufactured and tested, showing the proper fulfilment of the design requirements.

Interior Permanent Magnet Synchronous Machine (IPMSM) are high torque density machines that usually work under heavy load conditions, becoming magnetically saturated. To obtain properly their performance, this paper presents a node mapping criterion that ensure accurate results when calculating the performance of a highly saturated IPMSM via a novel magnetic reluctance network approach. For this purpose, a Magnetic Circuit Model (MCM) with variable discretization levels for the different geometrical domains is developed. The proposed MCM caters to V-shaped IPMSMs with variable magnet depth and angle between magnets. Its structure allows static and dynamic time stepping simulations to be performed by taking into account complex phenomena such as magnetic saturation, cross-coupling saturation effect and stator slotting effect. The results of the proposed model are compared to those obtained by Finite Element Method (FEM) for a number of IPMSMs obtaining excellent results. Finally, its accuracy is validated comparing the calculated performance with experimental results on a real prototype.

This paper studies the feasibility of using synchronous reluctance machines (SynRM) for low speed-high torque applications. The challenge lies in obtaining low torque ripple values, high power factor, and, especially, high torque density values, comparable to those of permanent magnet synchronous machines (PMSMs), but without resorting to use permanent magnets. A design and calculation procedure based on multistatic finite element analysis is developed and experimentally validated via a 200 Nm, 160 rpm prototype SynRM. After that, machine designs with different rotor pole and stator slot number combinations are studied, together with different winding types: integral-slot distributed-windings (ISDW), fractional-slot distributed-windings (FSDW) and fractional-slot concentrated-windings (FSCW). Some design criteria for low-speed SynRM are drawn from the results of the study. Finally, a performance comparison between a PMSM and a SynRM is performed for the same application and the conclusions of the study are summarized.

A computational fluid dynamics (CFD) model representing the effect of wafters in a totally enclosed electric machine is presented, introducing the most relevant theoretical assumptions and simplifications. The validation of the model is conducted through experimental measurements. From the CFD simulation data, a second-order response surface is developed using statistical tools, from which the wafters' influence on the convective heat transfer from the stator end windings is predicted. Wafter design criteria are obtained from the response surface information. Finally, a specific case is analysed, showing through CFD simulations that temperatures in the machine are reduced by including wafters in the design.

An analytical thermal model of an IC71W Induction Machine (IM) is presented, introducing the most relevant theoretical assumptions and equations. The validation of this model is conducted through experimental measurements. Some criteria for design of the most critical parts of the cooling system are provided using both a model based on Computational Fluid Dynamics (CFD) techniques and the analytical thermal model. First, the design of the water jacket and its main parameters are broadly analysed and some correlations for the design of the cooling ducts are presented. The influence of wafters on this cooling arrangement is also discussed.

This paper proposes, analyses and validates, both computationally and experimentally, an AC small signal model for a Trans quasi-Z-source inverter working in continuous conduction mode (CCM). For the implementation of the small-signal model, the dynamics of the particular Trans-gZSI network components have been considered. The presented AC small signal model is used for a detailed analysis of the performance of the Trans-gZSI topology, involving various aspects; a parametric study of the influence of the passive components on the dynamic response of the Z network, as well as the influence of their associated losses. Duty cycle and load variations are studied too, for Z topology operating point performance analysis. The AC small-signal model is then used to design a compensator for a closed -loop control scheme. Computer simulation results are presented to validate the model and the control method, comparing PSIM TransqZSI detailed simulations to the MATLAB derived results. Finally, experimental validation is achieved for the AC model in a low-medium power Trans-gZSI design, both in time and frequency domain. According to experimental results analysis, a snubber circuit is designed too, for the converter.