J. Rhett Mayor

Electromagnetic design considerations for a 50,000 rpm 1kW Switched Reluctance Machine using a flux bridge

The Switched Reluctance Machine (SRM) is a robust machine and is a candidate for ultra high speed applications. Until now the area of ultra high speed machines has been dominated by permanent magnet machines (PM). The PM machine has a higher torque density and some other advantages compared to SRMs. However, the soaring prices of the rare earth materials are driving the efforts to find an alternative to PM machines without significantly impacting the performance. At the same time significant progress has been made in the design and control of the SRM. This paper reviews the progress of the SRM as a high speed machine and proposes a novel rotor structure design to resolve the challenge of high windage losses at ultra high speed. It then elaborates on the path of modifying the design to achieve optimal performance. The simulation result of the final design is verified on FEA software. Finally, a prototype machine with similar design is built and tested to verify the simulation model. The experimental waveform indicates good agreement with the simulation result. Therefore, the performance of the prototype machine is analyzed and presented at the end of this paper.

Design of a 750,000 rpm switched reluctance motor for micro machining

This paper presents a detailed design process of an ultra-high speed, switched reluctance machine for micro machining. The performance goal of the machine is to reach a maximum rotation speed of 750,000 rpm with an output power of 100 W. The design of the rotor involves reducing aerodynamic drag, avoiding mechanical resonance, and mitigating excessive stress. The design of the stator focuses on meeting the torque requirement while minimizing core loss and copper loss. The performance of the machine and the strength of the rotor structure are both verified through finite-element simulations The final design is a 6/4 switched reluctance machine with a 6mm diameter rotor that is wrapped in a carbon fiber sleeve and exhibits 13.6 W of viscous loss. The stator has shoeless poles and exhibits 19.1 W of electromagnetic loss.

Intelligent Tool-Path Segmentation for Improved Stability and Reduced Machining Time in Micromilling

This paper presents the method of variable-feedrate intelligent segmentation as an enhanced approach to feedrate optimization in micromilling that overcomes detrimental scale effects in the process and leads to improved stability and decreased machining time. Due to the high tool-size to feature-size ratio present in micromilling, the maximum allowable feedrate is limited by the sampling rate of the real-time trajectory generation and motion control system. The variable-feedrate intelligent segmentation method is proposed to compensate for the feedrate limitation by intelligent selection of the interpolation technique applied to segments along the tool path in order to reduce the trajectory generation computation time and enable increased sampling frequency. The increased sampling frequency allows higher maximum feedrates providing for increased productivity and improved process stability. The performance of the novel intelligent segmentation approach was benchmarked against recent non-rational B-splines (NURBS) feedrate optimization techniques. Results from the numerical evaluation of the intelligent segmentation technique have demonstrated significant reductions in machining time, with a maximum reduction of over 50% recorded. Furthermore, the results from the study demonstrate the advantages of the intelligent segmentation method in enhancing process stability and maintaining, or marginally decreasing, process error. The variable feedrate intelligent segmentation method developed in this study provides, therefore, an enhanced methodology for path planning in high-speed, high-precision micromilling operations.

Generic electric machine thermal model development using an automated finite difference approach

The paper has shown the development of a generic model for the thermal analysis of stator geometries that when base lined against a standard thermal analysis program has shown similar accuracy and reduced computational time. This paper has also shown a technique for transforming typical stator geometries to a simplified geometry in polar coordinates.

Practical Considerations for the Design and Construction of a High-Speed SRM With a Flux-Bridge Rotor

The practical considerations for a 50,000 rpm switched reluctance machine (SRM) are studied in this paper. A novel rotor design topology with a flux bridge is proposed to reduce the windage losses at high speed. The electromagnetic characteristics of this design are analyzed in this paper. In addition, the practical problems of fabricating the prototype and testing it at high speed are discussed. Finally, experimental results are presented and compared with FEA simulation results.

Experimentation of an Electric Machine Technology Demonstrator Incorporating Direct Winding Heat Exchangers

A novel advanced cooling technique for electric machines, which is termed the direct winding heat exchanger (DWHX), is presented. This technique uses a microfeature enhanced heat exchanger that is inserted between the stator winding bundles. The DWHX is innovative, with the capability of generating large heat transfer coefficients, i.e., ~30 000 W/m2 · K, due to the small channel size and microfeatures. This cooling technique significantly reduces the thermal resistance from the stator windings to the ambient. The cooling technique is explained in detail, and an initial DWHX technology demonstrator electric machine is presented. The technology demonstrator is shown to be capable of steady current densities in excess of 24.7 A/mm2 and transient current densities in excess of 40 A/mm2 for class F insulation.

Optimal electromagnetic-thermo-mechanical integrated design for surface mount permanent magnet machines considering load profiles

Most existing design and optimization methods treat the electromagnetic, thermal and mechanical designs separately. As a result, the effects of power supply, machine control, load profile, thermal effects and materials are not fully integrated and accounted for, which often leads to over- or under- design. This paper proposes an innovative and computationally efficient approach which integrates the electromagnetic and thermo-mechanical design for Surface Mount Permanent Magnet (SMPM) machines. Particle Swarm Optimization (PSO) is part of this integrated process to efficiently find designs which optimize certain requirements, such as weight, efficiency, etc. for example. The effects of power supplies, machine controls, load profiles, thermal effects and materials can thus all be considered systematically in the proposed multi-physics design approach.

Calculating the electromagnetic field and losses in the end region of large synchronous generators under different operating conditions with three-dimensional transient finite element analysis

The significant losses in the end components due to the leakage magnetic field excited by the armature and field end windings can result in partial overheating and is an important consideration in the design of large synchronous generators. This paper describes an approach based on the three-dimensional (3D) transient finite element analysis (FEA) to determine the fields and losses in the generator end region. Taking the nonlinear/anisotropic properties of the stator core, as well as the slitting and stepping shape of core-end packets into consideration, the electromagnetic field and loss distribution in the end region is calculated. The method is validated by the agreement found between the temperatures predicted by the 3D stationary thermal FEA and the temperatures obtained from a physical measurement at various points in the generator. Then, the field and loss distributions in the end region under the open-circuit test condition, power factor lagging condition and leading condition are analyzed and compared using the proposed transient 3D FEA method.

Applicability of an orthogonal cutting slip-line field model for the microscale

Mechanical micromachining is a very flexible and widely exploited process, but its knowledge should still be improved since several incompletely explained phenomena affect the microscale chip removal. Several models have been developed to describe the machining process, but only some of them consider a rounded edge tool, which is a typical condition in micromachining. Among these models, the Waldorfs slip-line field model for the macroscale allows to separately evaluate shearing and ploughing force components in orthogonal cutting conditions; therefore, it is suitable to predict cutting forces when a large ploughing action occurs, as in micromachining. This study aims at demonstrating how this model is suitable also for micromachining conditions. To achieve this goal, a clear and repeatable procedure has been developed for objectively validating its force prediction performance at low uncut chip thickness (less than 50 μm) and relatively higher cutting edge radius. The proposed procedure makes the model generally applicable after a suitable and non-extensive calibration campaign. This article shows how calibration experiments can be selected among the available cutting trial database based on the model force prediction capability. Final validation experiments have been used to show how the model is robust to a cutting speed variation even if the cutting speed is not among the model quantities. A suitable set-up, especially designed for microturning conditions, has been used to measure forces and chip thickness. Tests have been performed on 6082-T6 Aluminum alloy with different cutting speeds and different ratios between uncut chip thickness and cutting edge radius.

Design, Development and Characterization of a Micro-Reactor for Fast Pyrolysis of Biomass Feedstocks

This paper presents the latest results in the design, development and performance characterization of a novel prototype micro-reactor system that is uniquely capable of capturing the transient product evolution history of the fast pyrolysis of biomass products. With strong demand driving the technological development of sustainable energy solutions, the consideration of optimal conversion methodologies for biomass energy feedstocks has received a great deal of attention recent years. [1, 2] The pyrolysis of soft woods, in particular spruce and pine, has emerged as a credible alternative to bio-digestive strategies that are reliant on fermentation processes, typically of corn feedstocks. The design objectives for the micro-reactor system are reviewed, highlighting the multi-physics and multi-disciplinary complexity in designing for transient characterization of the pyrolized products by the micro-reactor system. One of the dominant challenges in the design of the micro-reactor for fast pyrolysis reactions is the requirement of very high heating rates for the feedstock, on the order of 100°C/s. A 1D transient thermal model of the reactor is developed that considers the average particle size and morphology, the initial surface temperature of the reaction surface within the micro-reactor, the heat loss to the ambient atmosphere in the reactor, the heat loss through the contact resistance between the sample and the reaction surface and the thermal capacitance of the reaction surface. A parametric evaluation of the design space was performed using the 1D model in order to identify a preferred range of particle size, reactor surface area and thermal input power. Based on the results for the domain reduction study, multi-physics thermo-mechanical 3D FEA was used to undertake a brute-force optimization process of the final design. The key metric considered in the FEA study was the maximum thermal gradient in the reaction surface and was driven to a minimum value. The thermal response of the prototype micro-reactor has been evaluated using infra-red thermography measurement techniques. Thermographical analysis of the results has demonstrated negligible thermal gradients in the reaction plane up to the maximum reaction setpoint of 450°C. Based on the results of the thermal testing of the micro-reactor, the achieved peak heating rates of the sample have been estimated to be on the order of 400°C/s, meeting and exceeding the design requirement.Copyright