High-speed Electrical Machines Research Articles

Comparison of three measuring systems at high frequency for non oriented silicon steels: influence of the rolling direction on magnetic losses and B(H) curve

Loss data available in literature on laminated magnetic materials excited by alternating induction are often limited to rather low frequencies, (e.g., below 1 kHz). This is far below the frequencies experienced by materials used in high speed electrical machines. In this work, an appropriate measurement setup is used to evaluate losses in 0.35 mm thick iron silicon NO lamination up to an alternating peak induction of 1 T at a frequency of 10 kHz. In these conditions the capacitive effects are relevant on the B-coil and the H-coil when standard Epstein frame is used and might affect the measurements. A method to avoid this problem is proposed, based on a comparison between three characterization systems: a new single sheet tester that we use as a reference system, a conventional Epstein frame with 700 turns and a second Epstein frame with 200 turns dedicated to high-frequency. In the first part of the study we present an assessment of the limits of each system. An empirical correction factor is introduced to obtain the true loss value from measurement using the Epstein frame (700 turns from DC to 400 Hz and 200 turns from 400 Hz to 10 kHz). Finally, a comparison between two non-oriented FeSi of different quality and different thicknesses (0.35 mm and 0.2 mm) is presented in a wide range of frequencies (from DC to 10 kHz). Based on the loss separation theory, the skin effect on the two samples has been highlighted.

Amorphous and Nanocomposite Materials for Energy-Efficient Electric Motors

Fil: Silveyra, Josefina Maria. University Of Carnegie Mellon; Estados Unidos. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Solidos Amorfos; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Tecnologias y Ciencias de la Ingenieria; Argentina; Argentina

Skin effect in steel sheets under rotating induction

By means of a newly developed broadband measuring setup we have overcome the usual upper limit for the test frequency, around a few hundred Hz, which is encountered in the two-dimensional characterization of magnetic steel sheets at technical inductions and we have measured the rotational losses in low-carbon steels up to 1 kHz and peak induction 1.7 T. An important piece of information is thus retrieved upon a frequency range useful to predict the performance of high-speed electrical machines. Our experiments, performed on thick (0.640 mm) laminations, have brought to light the emergence of the skin effect under rotational fields. This is revealed by an abrupt deviation of the excess loss component, calculated under the conventional loss separation procedure, from its well-known linear dependence on the square root of the frequency. A simple magnetic constitutive law under rotating induction is proposed and introduced into the electromagnetic diffusion equation, which is solved by finite elements coupled to a non-linear algorithm. The classical rotational eddy current loss, largely prevalent with respect to the hysteresis and excess loss components on approaching the kHz frequencies in low-carbon steels, is then calculated in the presence of skin effect, permitting one to achieve full analysis of the rotational losses and good predicting capability upon a broad range of frequencies and peak inductions.

Combined FE and Particle Swarm algorithm for optimization of high speed PM synchronous machine

Purpose – The purpose of this paper is to optimize the stator slot geometry of a high-speed electrical machine, which is used as an assist for a turbocharger. Meanwhile, the suitability of the Particle Swarm algorithm for such a problem is to be tested. Design/methodology/approach – The starting point of the optimization is an existing design, for which the Particle Swarm algorithm is applied in conjunction with the transient time-stepping 2D finite element method. Findings – It is found that regardless of its stochastic nature, the Particle Swarm work well for the optimization of electrical machines. The optimized design resulted in an increase of the slot area and increase of the iron loss, which was compensated by a dramatic decrease in the Joule losses. Research limitations/implications – The optimization was concentrated on the stator design whereas the rotor dimensioning was carried out withing the compressor and turbine design. Originality/value – A turbocharger with electric assist is designed optimized and manufactured. The Particle Swarm algorithm is shown to be very stable.

Loss Calculation and Thermal Analysis of Rotors supported by Active Magnetic Bearings for High-speed Permanent Magnet Electrical Machines

The rotor overtemperature caused by losses is one of the important issues for the high-speed electric machine. This paper focuses on the loss analysis and thermal performance evaluation for a rotor of 100 kW, 32 km/min high-speed permanent-magnet motor. The rotor temperature distribution based on the finite element method is obtained by accounting for various losses, including air-friction loss of the rotor, iron loss of the active magnetic bearing, and eddy-current loss of the motor. The influence of the stator core temperature on rotor thermal performance is analyzed by using a coupling simulation of fluid-temperature field. The temperature rise measurement of rotor is employed to study the impact of different cooling way on rotor thermal performance and to verify the computational accuracy of losses and temperature distribution. The analysis result of air-friction loss is compared with the measurement, which is obtained from the total losses by using the method of loss separation. It has great significance for the cooling structure design and the efficiency enhancement of electrical machine.

Rotational Magnetic Losses in Nonoriented Fe–Si and Fe–Co Laminations up to the kilohertz Range

Literature data on the energy loss behavior of steel sheets under rotating induction are restricted to quite low frequencies, i.e., up to a few hundreds of hertz. This is not sufficient to predict the loss in high-speed electrical machines, where frequencies in the kilohertz range are commonly encountered. We have overcome this difficulty by making loss measurements under alternating and circular induction in 0.2 mm thick Fe-(3 wt%)Si and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">49</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">49</sub> V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sheets using a specially designed experimental setup. Peak polarization levels and frequencies up to 1.6 T at 2 kHz have been reached in the Fe-Si laminations, whereas the Fe-Co alloy, endowed with much higher permeability, has been characterized up to 2.1 T at 5 kHz. In the first part of this paper, the measured loss behavior versus peak polarization and magnetizing frequency is presented. In the second part, a loss model for circular induction is proposed, considering the skin effect. To this end, we have derived a simple magnetic constitutive law for the material, assumed to be isotropic, and we have introduced it into the electromagnetic diffusion equation. The solution of this equation by an iterative algorithm provides the induction profile across the sample thickness and eventually the classical loss component, which represents the major contribution to the total loss at high frequencies. Good agreement with the experiments is obtained.

2-D Analytical Subdomain Model of a Slotted PMSM With Shielding Cylinder

Due to their high efficiency and power density, permanent magnet synchronous machines (PMSMs) operating at high speed have recently gained a lot of attention. The development of high-speed PMSMs requires a good understanding of the physics related to the operation of such machines. Moreover, accurate modeling tools are needed when designing high-speed electrical machines. In this paper, the subdomain modeling technique is used to analytically compute the magnetic field of an electrical machine. The idea behind this technique is to divide the machine in a number of subdomains, in which the problem is simplified. The solutions in the different subdomains are then linked by imposing physical boundary conditions. The described model immediately considers the slotting effect and the eddy-current reaction field of a shielding cylinder (SC). The SC is a conductive sleeve, which is wrapped around the magnets. Its goal is to reduce the rotor losses at high-speed operation. This paper starts by introducing the applied modeling technique and the studied machine. Second, the basics of the model and its development are discussed. Finally, the results are compared with results of a finite-element (FE) model. A very good agreement between the proposed model and the FE model is observed. This implies that the developed model is indeed a powerful modeling tool for high-speed PMSMs. Moreover, it provides great insight in the machine's physics as well.

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

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.

High-speed electrical machines and drives [Special section intro.

This special section topic generated 53 papers submitted for peer review. Of these, only 19 papers have been accepted for publication. All the accepted papers include strong experimental activities to validate the proposed solutions. The special section starts with a paper presented by highspeed-machine specialists from Cummins together with the Guest Editors concerning the state of art of the high-speed electrical machines and drives. In this paper, a review of the current technologies used in high-speed electrical machine applications is discussed through an extensive survey of different topologies developed and built in the industry and academe. In addition, the developments in materials and components, including electrical steels and copper alloys, are also reported. The other 18 accepted papers have been grouped in several parts, taking into account their main topics. The Guest Editors provide an overview of the remaining 18 papers presented in this special section.

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

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.

A 120 °C Ambient Temperature Forced Air-Cooled Normally-off SiC JFET Automotive Inverter System

The degree of integration of power electronic converters in current hybrid electric vehicles can be increased by mitigation of special requirements of these converters, especially those regarding ambient air and cooling fluid temperature levels. Today, converters have their own cooling circuit or are placed far away from hot spots caused by the internal combustion engine and its peripheral components. In this paper, it is shown, how the use of SiC power semiconductors and active control electronics cooling employing a Peltier cooler can help to build an air-cooled inverter system for 120 °C ambient temperature. First, a detailed analysis shows, how the optimum junction of this high-temperature system can be calculated. Then, the operating temperature ranges of power semiconductors, thermal interface materials, capacitors, and control electronics are investigated, leading to a comprehensive analysis of mechanical concepts for the inverter system in order to show new ways to solve electrical and thermal tradeoffs. In particular, the operation of the signal electronics and the gate driver for power semiconductors with a junction temperature of 250 °C within the specified operating temperature range is ensured by appropriate placement and cooling methods, while taking the electrical requirements for limits on the wiring inductances and symmetry requirements into account. The analysis includes an accurate thermal model of the converter and an optimized active cooling of the signal electronics using a Peltier cooler. Finally, a hardware prototype with discrete power semiconductor devices and thus with a junction temperature limit of 175 °C driving high-speed electrical machines is shown to validate the theoretical considerations in a custom-designed high-temperature test environment.

Fully Processed Fe–Co Soft Magnetic Laminations for High-Speed Electrical Machines

Unlike the research conducted in the last few decades toward inhibitor-precipitate-aided high-strength FeCo strips, a high strength process (HSP) based on continuous annealing and partial recrystallization is proposed starting from usual industrial Fe49Co49V2 melts and cold-rolled strips. With the help of improved ductility phenomenon in such metallurgical state and of ordering avoided by fast cooling, smart and coexisting working properties have been demonstrated: wide and controlled yield stress up to at least 1000 MPa even applied to thin laminations, easy punch into parts from the HSP strip, ability to get by an added final annealing-if needed-low magnetic losses for punched parts, high stability of parts geometry through a subsequent static annealing, and good aging stability. To get the full benefit of such improvements in many electrotechnical applications, this promising new grade family has yet to be deeply characterized (aging, anisotropy, and creep) and improved in performance (losses and permeability).

Study of a High-Speed Motorization With Improved Performances Dedicated for an Electric Vehicle

This paper presents the study of an entirely electromagnetic traction system to be used for electric vehicle (EV) application. To have a reduced mass and compact system, the electric motor will work at 40500 r/min. Usually, the high-speed electrical machines are rather used for ventilation or compressor systems, with low dynamics. The high variation of the load torque in EV application demands the best possible mechanical/energetic performances. The traction system proposed here is composed by a high-speed permanent magnet motor linked to a magnetic gear. This paper will present the technology of the entirely electromagnetic traction chain and its energetic and mechanical performances. The results are validated numerically through finite-element analysis.

Overview of Bearingless Permanent-Magnet Synchronous Motors

Bearingless permanent-magnet (PM) synchronous motors (BPMSMs) are a new type of machines combining the characteristics of conventional PM synchronous motors and magnetic bearings. With ever-increasing concerns on applications, such as high-speed electric machines, canned pumps, high-speed-precision mechanical processing, aeronautics and astronautics, flywheel energy storage, life science, vacuum technique, and semiconductor and biotechnology industries, there is a fast growing interest in BPMSMs. In this paper, after a general description of the generation principle of radial suspension forces, a comprehensive overview of BPMSMs is presented, with particular emphasis on mathematical models, motor topologies, and control strategies. Moreover, several possible development trends of the BPMSM are also discussed.

A Study on the Design Procedure of the Eight Pole Magnetic Bearings for the Inner-rotor and the Outer-rotor Type

This paper presents design procedure of the magnetic bearings used for high-speed electric machines and flywheel energy storage systems. Magnetic bearing can be categorized by inner-rotor type and outer-rotor type according to the position of the rotary disc. These two types are applicable based on application environments such as application space, required attraction force, and controllability. Magnetic bearing is generally designed based on the ratio (geometrical coefficient or geometrical efficiency) of pole width to rotor journal radius but proper ratio is only decided by the analysis. This is the difficulty of the magnetic bearing design. In this paper, proper design technology of the inner-rotor type and outer-rotor-type eight pole magnetic bearings is introduced and compared with the FEM analysis results, which verifies the proposed design procedure is suitable to be applied to the design of the magnetic bearings for the industrial applications and flywheel energy storage system.

Design and Characterization of an E-booster Driven by an High Speed Brushless DC Motor

Engine downsizing has become one of the main strategies to reduce C02 emission. Turbochargers are well-adapted to this purpose but one of their biggest drawbacks is the turbo-lag which reduces the driving comfort especially during acceleration. Electrically driven compressors also known as E-compressor or E-booster could be a well-adapted solution to boost the engine intake pressure in order to reduce the turbo-lag. Since centrifugal compressors operate at high rotational speeds, high speed electric machines are therefore required. To achieve a significant reduction of the turbo-lag, a very fast response time is needed leading to the development of electric machines able to typically spin from idle to 75kRPM in less than 300ms. With 20 years of expertise in the development of innovative brushless DC motors for automotive applications, MMT has recently investigated the design of such high power-high rotation speed motors. After first integrated an electric motor into a turbocharger described in [1], MMT has decided to optimize the complete system in collaboration with SwissAuto Wenko AG, a specialist in the design and characterization of advanced charging systems. The initial specification was an overpressure of 1.3 within 300ms, reached by using a 2kW@80kRPMs electric motor. The motor optimization, the mechanical design of the system as well as experimental measurements are presented. Details about the brushless DC motor design will be given as well as compressor maps and transient response behaviors. Results will also show that the transient state performances are better than expected.

Stator Design and Air Gap Optimization of High Speed Drag-Cup Induction Motor using FEM

A huge number of modern applications nowadays require the use of high speed electrical machines which need to be highly optimized in order to achieve the best efficiency and the lowest ...

Study on Stiffness and Damping Characteristic of Hybrid Magnetic Bearing for High-Speed Electrical Machine

This paper focuses on the stiffness and damping characteristic of hybrid magnetic bearing for high-speed electrical machine. Firstly, it analyzes the structure and working principle of hybrid magnetic bearing, according to the bearing’s magnetic circuit properties, it deduces the equation of the bearing’s magnetic force with displacement and current. Then, combining with the controller parameters it deduces the stiffness and damping equation of magnetic bearing. At last it simulates the stiffness and damping characteristic curve, and the obtained simulation results can give theoretical support for rotor dynamic analysis and modal analysis.

The Strength Analysis of Rotor Sleeve and PM for High-Speed Electrical Machine

For high-speed permanent magnet (PM) electrical machine, the PM material has very small tensile stress, and it can’t withstand the huge centrifugal force. So, a high-strength sleeve with interference fit is necessary to protect the PM. This paper mainly analyzes the strength of rotor sleeve and PM. It deduces the theoretical calculation method of the strength according to Lame equation, and it also analyzes the stress of sleeve and PM by ANSYS Workbench. The result show that the theoretical calculation value is closely to the ANSYS result, and it can meet the requirements of protecting the permanent magnet in high rotation speed.

A Five-/Nine-Level Twelve-Switch Neutral-Point-Clamped Inverter for High-Speed Electric Drives

A five-/nine-level twelve-switch inverter is described for three-phase high-speed electric machines having a low per-unit leakage reactance. By reducing the voltage blocking requirement of the semiconductors, the neutral-point-clamped (NPC) variant of the coupled inductor (CI) inverter topology (NPC-CI) is more suited to high dc bus voltages than the six-switch alternative (six-switch CI). Operational and design details are described for the NPC-CI inverter using a three-limb inductor core, including practical considerations for the inverter construction and operation, 480 V/208 V inductor mass comparison between six- and twelve-switch topologies, natural voltage balancing of the split-capacitor dc link, and voltage stresses of the freewheel diodes. Improvements in machine performance are illustrated using two experimental test rigs: an unloaded 18 000-r/min 15-hp induction machine to illustrate improved harmonic quality when operating with a limited switching frequency and a high fundamental output frequency, and a loaded 2-hp utility speed induction machine to demonstrate transient performance.