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

Energy storage systems (ESSs) play a very important role in recent years. Flywheel is one of the oldest storage energy devices and it has several benefits. Flywheel Energy Storage System (FESS) can be applied from very small micro-satellites to huge power networks. A comprehensive review of FESS for hybrid vehicle, railway, wind power system, hybrid power generation system, power network, marine, space and other applications are presented in this paper. There are three main devices in FESS, including machine, bearing, and Power Electronic Interface (PEI). Furthermore, advantages and disadvantages all of them have been presented. In addition a brief review of new and conventional power electronic converters used in FESS, have been discussed. Finally, practical ways to develop this technology in the future are presented.

A comprehensive review of Flywheel Energy Storage System technology

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

In flywheel based energy storage systems (FESSs), a flywheel stores mechanical energy that interchanges in form of electrical energy by means of an electrical machine with a bidirectional power converter. FESSs are suitable whenever numerous charge and discharge cycles (hundred of thousands) are needed with medium to high power (kW to MW) during short-time periods (seconds–minutes). Monitoring of the FESS state of charge is simple and reliable as only the spinning speed is needed. The materials for the flywheel, the type of electrical machine, the type of bearings and the confinement atmosphere which all together determine the FESSs energy efficiency (>85%) are reviewed. Main FESS applications: power quality, traction and aerospace are presented. Additionally in this paper it is presented the simulation of an isolated wind power system (IWPS) consisting of a wind turbine generator (WTG), a consumer load, a synchronous machine (SM) and a FESS. A low-speed iron flywheel driven by an asynchronous machine (ASM) is sized for the presented IWPS. The simulation results with graphs for system frequency, system voltage, active powers of the different elements, and FESS-ASM speed, direct and quadrature currents are presented showing that the FESS effectively smoothes the wind power and consumer load variations.

Flywheel energy storage systems: Review and simulation for an isolated wind power system

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

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

Slotless machines have been applied for a very high rotational speed and/or the ripple-free torque. In this paper, slotless machines equipped with external 4-pole field Halbach and radially magnetized PM array for electro-mechanical battery. This paper describes the comparison of the design guidelines, magnetic field characteristics, required magnet volume and optimal thickness of windings for two types of PM rotors.

Design and analysis of high speed slotless PM machine with Halbach array

The rotational loss is one of the most important problems in high-power flywheel energy storage system (FESS) which supplies the electrical energy from the mechanical rotation energy. In our FESS with PM synchronous motor/generator (PMSM/G) and non-contacting system, the rotational loss is mainly generated in the laminated iron stator when PM rotor mounted on the flywheel is rotated. Therefore, this paper presents design and evaluation of a PMSM/G model composed of double-sided Halbach magnetized PM rotor and ironless 3-phase winding stator to minimize speed reduction of the flywheel. For one such motor structure we give analytical formulae for its magnetic field and back-electromotive force in a uniform way via the magnetic vector potential. As a result of experiment, dynamic performance of a manufactured double-sided PMSM/G is evaluated by comparison with those of the slotless PMSM/G in the idling mode. The result shows that the presented PMSM/G can be applicable to the high-power FESS.

Design and Experimental Evaluation of Synchronous Machine Without Iron Loss Using Double-Sided Halbach Magnetized PM Rotor in High Power FESS

The paper reports on the comparison of three types of permanent magnet machines as the motor/generator for an electromechanical battery. To apply to high-speed drives, slotted, slotless ring-wound and coreless Halbach machines are designed to have the same capability and limited size. Three types are also compared with respect to their topology, size, magnetic field, inductance, torque and generating voltage, loss, and efficiency.

Sang-Kyu Choi

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

Design and analysis of high speed slotless PM machine with Halbach array

Design and Experimental Evaluation of Synchronous Machine Without Iron Loss Using Double-Sided Halbach Magnetized PM Rotor in High Power FESS

Comparison of three types of PM brushless machines for an electro-mechanical battery