This paper reviews the current technologies used in high-speed electrical machines through an extensive survey of different topologies developed and built in the industry and academia for several applications. Developments in materials and components, including electrical steels and copper alloys, are discussed, and their impact on the machines' operating physical boundaries is investigated. The main application areas pulling the development of high-speed machines are also reviewed to better understand the typical performance requirements.

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High-Speed Electrical Machines: Technologies, Trends, and Developments

The high-speed (HS) electric machines are gaining attention in several different applications, and the development of advanced materials, electronic components, and control algorithms is pushing ahead the technological speed limits. In the electromagnetic sizing of HS machines, the mechanical and thermal involvements are very tight to make it necessary to deal with all the different aspects at the same time. This paper aims to summarize and discuss the electrical and the mechanical aspects involved in the HS machine design, highlighting the main issues and the tradeoffs that the designer has to consider. Furthermore, the correlation between volume reduction and speed increase, based on commercial high-frequency rotor-stator units, is also presented.

Electrical Machines for High-Speed Applications: Design Considerations and Tradeoffs

Permanent-magnet (PM) machines are considered the most suitable machine type for very high speed applications. Still, due to the growing demand for the ever higher rotational speeds, PM machines are approaching their limits. The focus of this paper is the different factors that lie behind the inherent speed limitations of PM machines. The limits-thermal, elastic, and rotor dynamical-are defined, classified, and correlated to basic machine parameters.

On the Speed Limits of Permanent-Magnet Machines

Linear Synchronous Motors: Transportation and Automation Systems

The maximum-power limits for high-speed permanent-magnet (PM) electrical machines for air compressor applications are determined in the speed range 20000-100000 r/min. For this purpose, five PM machines are designed and the electromagnetic, thermal, and mechanical designs of each machine are simultaneously performed. The critical values of the thermal and mechanical constraints are considered in order to obtain the maximum powers of the electrical machines. The electromagnetic losses generated in the machine are the output parameters of the electromagnetic design and input parameters for the thermal design. The thermal design is performed using a multiphysics method, which couples computational-fluid-dynamics equations with heat-transfer equations. The mechanical design considers the retention of the rotor elements against the huge centrifugal forces that arise during the high-speed operation and also the rotor dynamics properties of the rotor. The reliability of these design techniques is experimentally validated in the paper. The obtained maximum-power limit defines the speed-power region, in which the high-speed PM electrical machines intended for compressor applications can have a safe operation.

Power Limits of High-Speed Permanent-Magnet Electrical Machines for Compressor Applications

This paper describes the design and analysis of a high-speed and high-power density BLDC motor for a 50-kW, 70 000-rpm class centrifugal compressor. Design criteria and power loss analysis of the high-speed machine structure are described by analytical method, and the results are validated by finite element method. And then, the prototype machine has been fabricated and tested. The experimental results confirmed the validity of the proposed design and analysis scheme of the high-speed BLDC motor

Design and Analysis of a High-Speed Brushless DC Motor for Centrifugal Compressor

Recently, high-speed centrifugal turbo-compressors have been under intensive research and development. Since, compared to conventional compressors, high-speed centrifugal compressors have numerous qualities such as simple structure, light weight, small size, and high efficiency, etc. In order to maintain the mechanical integrity of a high-speed permanent magnet (PM) machine rotor intended for high-speed operation, the rotor assembly is often retained within a stainless steel or carbon-fiber sleeve. The sleeve is exposed to fields produced by the stator from either the slotting or the mmf harmonics that are not synchronous with the rotor. These non-synchronous fields cause the significant rotor losses. An optimum design of PM machines requires the accurate prediction for these rotor losses. On the basis of analytical field analysis and 2D finite element analysis (FEA), this paper deals with the rotor losses in high-speed PM machine. In particular, the difference of the rotor losses between the Inconel718 and Carbon-Fiber/Epoxy sleeve is quantitatively made clear in this work.

A Design Approach to Reduce Rotor Losses in High-Speed Permanent Magnet Machine for Turbo-Compressor

This paper discusses the braking torque and normal force analysis of axial flux permanent magnet (AFPM)-type eddy current brakes (ECB) on the basis of an analytical field computation using a space harmonic method. On the basis of the magnetic vector potential and a 2D polar coordinate system, permanent magnets considering the eddy current effect are obtained. Additionally, by utilizing the derived analytical field solutions, the braking torque and normal force are predicted. Finite element analysis is employed to confirm the validity of the analysis and compare it with the experimental results obtained from the prototype AFPM-type ECB.

Analytical Torque Calculations and Experimental Testing of Permanent Magnet Axial Eddy Current Brake

For permanent-magnet synchronous motors driven by high-frequency drives, the rotor speed is normally above 30 000 rpm, and it may exceed 100 000 rpm. Designing high-speed motors from both in an electromagnetic and a mechanical aspect requires a different approach from designing conventional motors with low-medium operation speeds. This paper deals with rotor natural frequencies that are particular to high-speed permanent-magnet synchronous motors for turbo-compressor applications. It is very important to accurately predict rotor natural frequencies at the design stage in order to minimize operational failure. On the basis of the finite element method (FEM), this paper predicts the natural frequencies of a designed and manufactured permanent magnet rotor. The experimental results confirm the validity of the FEM calculations of the proposed design process.

Rotor Natural Frequency in High-Speed Permanent-Magnet Synchronous Motor for Turbo-Compressor Application

This paper deals with analysis and experiments of moving-magnet linear actuators with cylindrical Halbach arrays. On the basis of analytical two-dimensional field solutions, this paper predicts magnetic fields, thrust, flux linkage, and back electromagnetic fluctuation. The results are validated extensively by comparison with finite element analysis. Test results such as thrust measurements are also given to confirm the analysis.

Han-Wook Cho

Papers

Design and Analysis of a High-Speed Brushless DC Motor for Centrifugal Compressor

A Design Approach to Reduce Rotor Losses in High-Speed Permanent Magnet Machine for Turbo-Compressor

Analytical Torque Calculations and Experimental Testing of Permanent Magnet Axial Eddy Current Brake

Rotor Natural Frequency in High-Speed Permanent-Magnet Synchronous Motor for Turbo-Compressor Application

Analysis and experimental verification of moving-magnet linear actuator with cylindrical Halbach array