High-speed Electrical Machines Research Articles

Optimization of conductors arrangement in slot for alternating current winding losses reduction

PurposeThe purpose of this study is to evaluate and minimize the losses of alternating current (AC) in the winding of electrical machines. AC winding losses are frequently disregarded at low frequencies, but they become a significant concern at high frequencies. This is the situation where applications require a high speed. The most significant applications in this category are electrical propulsion and drive systems.Design/methodology/approachAn analytical model is used to predict the AC losses in the winding of electrical machines. The process involves dividing the slot into separate layers and then calculating the AC loss factor for each layer. The model aims to calculate AC losses for two different winding arrangements involving circular conductors. This application focuses on the stator winding of a permanent magnet synchronous motor that is specifically designed for electric vehicles. The model is integrated into an optimization process that makes use of the genetic algorithm method to minimize AC losses resulting from the arrangement of conductors within the slot.FindingsThis study and its findings demonstrate that the arrangement of the conductors within the slot has a comparable effect on the AC losses in the winding as the machine's geometric and physical properties. The effectiveness of electrical machines depends heavily on optimizing the arrangement of conductors in the slot to minimize AC winding losses.Originality/valueThe proposed strategy seeks to minimize AC winding losses in high-speed electric machines by providing a cost-effective and precise solution to improve energy efficiency.

Influence of Scallops on Windage Loss and Flow Characteristics in Disk-Type Gap

Abstract Windage loss and flow characteristics in a disk-type gap featuring scalloped structures are investigated in this paper. Special attention is paid to the size of the scallops and the associated loss models. The respective losses and scallop effects in the gap are explored with various combinations of depths, quantities, and rotating speeds. The results indicate that scallop structures positively contribute to increased windage losses, accounting for more than 60% of the overall losses. An internal spiral vortex band is formed along the scallop wall, with the scallop depth ratio exerting influences on loss, reaching a maximum of 8.1%. The current scallop loss model overlooks the consideration of the total arc length ratio of scallops to the circumference, presenting a limitation, and the maximum relative deviation from numerical simulation results is observed to be 111.4%. An increase in arc length ratio results in a higher total loss, although the loss per individual scallop is diminished, manifesting in reduced vortices and pressure differences. Furthermore, a modified model is proposed to increase the precision of the current loss model. The maximal relative deviations of 13.8% confirm that the modified model is accepted to predict the windage loss in disk-type gaps with scallops. The conclusions offer valuable insights into the structural design of impellers and high-speed electrical machines with superior efficiency.

AC Loss Analytic Method and Optimization of Litz Winding for High-Speed Electrical Machines

AC Loss Analytic Method and Optimization of Litz Winding for High-Speed Electrical Machines

Combined Electromagnetic and Mechanical Design Optimization of Interior Permanent Magnet Rotors for Electric Vehicle Drivetrains

In many high-speed electrical machines, centrifugal forces within the rotor can be first-order constraints on electromagnetic optimization. This can be particularly acute in interior permanent magnet (IPM) machines in which magnets are usually retained entirely by the rotor core with no additional mechanical containment. This study investigates the nature of the trade-off between mechanical and electromagnetic requirements within the context of an eight-pole, 100 kW IPM machine with a base speed of 4000 rpm and an extended speed range up to 12,000 rpm. A series of mechanical and electromagnetic models are used to estimate the level of shaft interference, mechanical stress in critical regions of the rotor and the impact of various features and dimensions within the machine on electromagnetic torque. A systematic exploration of the design space is undertaken for rotor diameters from 120 mm to 180 mm, with optimal designs in terms of torque per unit length established at each diameter while meeting the constraints imposed on mechanical stress. The final preferred design has a rotor of 165 mm and an axial length of 103 mm long with a fractional slot winding in a 30-slot stator. The overall machine has an active mass of 42.3 kg, which corresponds to ~2.4 kW/kg. This paper describes the optimization study in detail and draws on the results to explore the nature of the design trade-offs in such rotors and the impact of core properties.

Equivalent 2-D FEA Modeling Method for AC Loss Analysis of High-Speed Electrical Machines With Litz Winding Considering Incomplete Transposition

In high-speed electrical machines, litz wire shows great performance on reducing the AC loss under complete transposition, which is well-known. However, due to technological limitation, its pitch cannot be made to match the stack length in small aspect ratio machines, bringing significant AC loss. And 3D FEA modeling method is too complicated for its twisted structure and time-consuming. This paper proposed an equivalent 2D FEA modeling method for high-speed electrical machines with litz winding. The machine is divided into several parts along the axial equally, and each part is established by a 2D FEA model approximatively in which litz winding transposition is considered. All 2D models are connected in series in field-circuit coupling model. The influences of structural parameters on AC loss are also analyzed, providing guidance for the optimal design of litz winding in high-speed electrical machines.

Material Tradeoff of Rotor Architecture for Lightweight Low-Loss Cost-Effective Sustainable Electric Drivetrains

The art of the successful design of high-speed electrical machines comes with many challenges in the mass, size, reliability, and energy efficiency. Material engineering of electrical machines has been identified as a key solution for higher power dense electric drivetrains. One of the main challenges at high speed is the eddy-current losses in the active electromagnetic parts, especially magnetic materials and permanent magnets (PMs). This study is devoted to the selection of PM rotor materials using multidisciplinary design optimization for a high-speed electric drivetrain. Beside AC loss minimization, more disciplines are considered, such as the minimization of weight, and cost. Different laminations are investigated with different magnetic properties as well as cost. Additionally, different PMs are optimized considering low-cost ferrite and high-coercivity permanent magnets (HCPMs). Moreover, the optimal materials are identified which have the best balance between loss, weight, cost, ripples. Finally, different rotor designs are prototyped, assembled, and tested using the same stator configuration. Also, the best rotor design is selected, and the electromagnetic performance is measured and compared with conventional designs. The optimal design results in 8% extra torque with at least 20% weight reduction.

A Novel Sleeve Design to Reduce the Eddy Current Loss of High-Speed Electrical Machines

Demand for high-speed motors is increasing. Surface-mounted permanent magnet synchronous motors (SPMSM) used in high-speed applications have magnets attached to the rotor, so there is a risk of damage and scattering due to centrifugal force as the speed increases. For this reason, applying the retaining sleeve to the rotor is essential. However, when using sleeves, there is a problem of reducing efficiency due to eddy current loss. In this paper, a study was conducted on a motor for a 100 kW building air conditioning system operating at a speed of 20,000 rpm. The purpose of the study is to reduce eddy current loss by optimizing the sleeve geometry. To this end, 3D finite element analysis (FEA) using JMAG 22.1 was conducted to analyze eddy current loss, the minimum safety factor was analyzed through mechanical stiffness analysis using ANSYS Workbench, and the validity of sleeve shape was proved through cause analysis. Through the research results, it is expected that the shape change of the sleeve will have the effect of reducing eddy current loss.

Design and Experimental Analysis of an Ultra-High Speed Switched Reluctance Machine With Aerostatic Bearings

High-speed electric machines have become a hot research topic in recent years. Switched reluctance machines (SRMs) are good candidates for high speed applications due to their simple rotor structure without magnets. However, the double-salient structure of conventional SRM rotors are not suitable for ultra-high speed applications due to the high windage friction. In this paper, a novel ultra-high speed SRM is proposed using a solid cylindrical rotor. A detailed electromagnetic design of dimension calculation, air-gap calculation, material selection, winding selection, windage torque calculation, drive system and control strategy are presented. A closed loop control model is built using Maxwell/Simplorer co-simulation to estimate the performance of the machine. Then, in order to explore the feasibility of using other types of bearings for SRMs than ball bearings at ultra-high speeds, the machine is prototyped and integrated with aerostatic bearings. Detailed experimental results are presented. The measured inductance and current profiles match the design value well. However, the unexpected large windage friction beyond 40,000 rpm prevents the motor from reaching even higher speeds beyond 90,000 rpm. Some possible reasons are suggested to explain this interesting phenomena.

Optimized rotor structural design methodology for high-speed electrical machines based on mechanical characteristics

In high-speed electrical machines (HSEM), mechanical vibration associated with critical speeds of rotor systems can be detrimental to the machine operational stability, especially for vibration near resonances. The structural sizing of a rotor system is often constrained to its mechanical parameters, such as its overall weight, maximum torque, and rated power, which complicate the design, necessitating an iterative design optimization process. This work presents a systematic and iterative rotor structural sizing optimization methodology that incorporates semi-analytical and numerical modeling, specifically taking into account multiple mechanical design parameters from the static, rotordynamic, and electromagnetic-thermal evaluation. The proposed methodology provides an effective design optimization procedure for a general application of HSEM to accelerate its design process, by which the power density and the dynamics stability during high-speed operation are optimized simultaneously. A parametric analysis was carried out where a 24-kW, 12,000-rpm aviation starter-generator was optimized. It was demonstrated that the power density of the machine could be increased by 14.7% from 2.3 to 2.6 kW/kg, while the critical speed was increased by 128.6% from 1,400 to 3,200 Hz.

Surrogate Model-Based Multiobjective Optimization of High-Speed PM Synchronous Machine: Construction and Comparison

This article employs surrogate models for large-scale high-speed (HS) electrical machine optimization to reduce heavy computational burden caused by the finite-element method (FEM) based on nondominated sorting genetic algorithm II. Three artificial neural networks, namely, multilayer perceptron (MLP), support vector regression (SVR), and generalized regression neural network (GRNN), and the classical Kriging model are developed based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula> -fold crossing validation method. To find out the most suitable surrogate model, a HS permanent magnet synchronous machine (PMSM) applied in electrically assisted turbocharger (EATC) considering its multiphysics characteristics is optimized by different models. A detailed comparison is provided in terms of prediction accuracy and modeling time consumption. The optimal design is verified to guarantee the accuracy of optimization results. The key contributions of this article include an automatic HSPMSM optimization process is proposed, where complete modeling and tuning method as well as a reasonable comprehensive evaluation metric of different surrogate models are conducted. It is found that invalid samples from the initial dataset contain useful information to improve prediction accuracy. Hence, an entire surrogate process should benefit from a pretrained classifier. Also, it reveals that MLP, SVR, and Kriging model can greatly improve the design optimization effectiveness with high accuracy, whereas GRNN is not suitable for this specific optimization scenario.

Development of dual phase soft magnetic laminate for advanced electric machines

The development of dual phase soft magnetic laminate for advanced electric machines at General Electric is summarized, including alloy development, properties, manufacturing trials, prototype experience, potential applications, and future material development. Dual phase soft magnetic laminates provide the flexibility to tune magnetic/non-magnetic state at the desired locations, using solution nitriding treatment with protective mask/coating. This enabling material technology benefits electric machine performance by reducing flux leakage in the laminates. It also decouples the electromagnetic and mechanical design, which opens up the design space for advanced electric machines. Magnetic and mechanical properties of dual phase laminates were compared to commercial FeSi and FeCo soft magnetic laminates. Driven by the market needs for high power density and high-speed electric machines, a synchronous reluctance (SynRel) machine without PMs using dual phase soft magnetic laminates was assessed in machine electromagnetic performance as well as rotor stress analysis by finite element simulation. Successful prototype build and testing further retired manufacturing risks and advanced the technology maturity level. Future material development with higher mechanical strength, higher saturation magnetization, higher permeability, and lower loss are highly desired for ground and air transportation electrification.

Development of Novel Semi-Stranded Windings for High Speed Electrical Machines Enabled by Additive Manufacturing

Recent advances in electrical machines and energy storage technologies make electric vehicles (EVs) feasible replacements to conventional internal combustion engines. One of the main challenges of high speed electrical machines is providing maximum output power with minimum energy losses, weight, and volume. At high frequency operation, the conductors of AC electrical machines can suffer from skin and proximity effects. This results in high AC losses in the machine windings and can eventually lead to machine failure. In this paper, a novel design for a semi-stranded coil is proposed to limit these undesirable effects. Enabled by additive manufacturing (AM) technology, this sophisticated design is 3D printed using ultralight aluminum alloy. Finally, the AC performance of this coil is measured and compared with conventional single-strand copper coil at different frequency levels. It is found that the proposed design can effectively limit the eddy current losses in the high frequency domain.

Optimal Design of High-Speed Electric Machines for Electric Vehicles: A Case Study of 100 kW V-Shaped Interior PMSM

The need of compact machines increased in recent years due to increases in raw materials’ price. Hence, many studies are currently being conducted on high-speed challenges to propose an optimal design methodology. AC losses in windings are often not included in the optimization process and are treated in post-processing by choosing a suitable conductor’s diameter to mitigate skin and proximity effects. This paper presents an optimization and design methodology for high-speed electric machines considering these losses, using models with an interesting trade-off between computation time and accuracy, which is helpful for large-scale optimization, in which more than 9,600,000 machines are evaluated. Optimizations are conducted on 100 kW high-speed one-layer V-shaped interior permanent magnet synchronous machines, widely used in vehicles thanks to their high power density, based on the specifications of the Peugeot e208, for different values of pole pairs and maximum speed. The influence of lamination thickness, fill factor, and maximum current density on the optimal design is also investigated. This paper concludes the utility of increasing speed to achieve high power density and proposes best alternatives regarding automotive constraints. Results show that the number of pole pairs is not always a key parameter in obtaining the lowest volume, especially at high speed.

Multidisciplinary Design Overview and Comparison for Two Case Studies of High Speed Permanent Magnet Machines

High-speed electrical machines have become more and more popular applications driven by electric vehicles and all-electric aircraft. Their design usually requires a high level of integration, including loss, thermal, cooling, and mechanical aspects. This article makes a comprehensive overview of the multidiscipline design method of high-speed permanent magnet (HSPM) machines. A 4-kW machine with the flexible rotor operating above the first bending critical speed is presented, and a 30-kW machine is also developed with consideration of the multidisciplinary design process for contrast. The constraint and the mechanism in the overview are investigated to clarify the influence of different design variables on the rotor structure and performance. Finally, two machines are fabricated and tested, and the values are compared with theoretical results.

Suppression of Winding AC Copper Loss in High-Speed Electrical Machines by a Practical Transposition Technique

The ac copper loss, which results from the skin effect, the proximity effect, and the bundle-level circulating current, is widely concerned in high-speed electrical machines since they grow rapidly with the frequency. While the skin effect can be easily suppressed by the utilization of thinner wires, the circulating current is generally restrained by a complicated transposition technique. Moreover, the transposition technique is better suited to the preformed winding other than the random-wound winding, hence, it is still difficult to suppress the circulating current ac loss in the random-wound winding. In this article, a practical transposition technique is proposed for the circulating current loss suppression for high-speed electrical machines with random-wound windings. To implement this technique, a specific winding former is designed and manufactured. The proposed transposition technique is verified in a 200 kW, 54 000 r/min high-speed permanent magnet machine, contributing to a reduction of 55.2% copper loss compared to the untransposed winding. The experiment result indicates that the proposed transposition technique is practical in engineering.

Convection Heat Transfer Coefficient Regression Models Construction for Fast High-Speed Motor Thermal Analysis

This article proposes a computationally efficient thermal study method that substitutes computational fluid dynamics (CFDs) with a finite-element analysis (FEA) involving minimal loss of accuracy and omission of the increased computational load. The suggested technique contributes toward the realization of multiphysics optimization of high-speed electrical machines that effectively includes critical thermal evacuation phenomena. The strategy is regression-based and succeeds in constructing convection coefficient regression models that typically involve many variables and small training datasets. The proposed scheme is verified in high-loss density and high-speed outer rotor surface-mounted permanent magnet (SMPM) motor geometries that an optimization algorithm typically encounters during execution. The reference target specifications correspond to 20 kW output power, 15k r/min rotating speed, and 2 kHz electrical frequency.

Microstructure and Mechanical Properties of Steel and Ni-Based Superalloy Joints for Rotors of High-Speed Electric Motors.

High-speed electric motors, e.g., axially laminated anisotropic synchronous reluctance motors (ALA-SynRM), use a solid rotor manufactured by joining alternating layers of magnetic and non-magnetic metallic sheets. The strength of the dissimilar metallic joints is critical for the rotor’s ability to withstand the operating conditions of the high-speed electrical machine. In this work, various dissimilar metallic joint configurations that can be used in high-speed ALA-SynRM rotors are studied by analyzing the shear strength, microstructure, hardness, and composition of the joints. Metallic joints of structural steels and Inconel® alloys fabricated by vacuum brazing and hot isostatic pressing (HIP) are studied. Finite element analysis (FEA) was performed to calculate the maximum shear stress of the joints that were subjected to various high speed operating conditions. The shear strength of the test specimens was measured and compared with FEA results. The microstructure and chemical composition of the joints were studied by using optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) on SEM. The results show that the hot isostatic pressed S1100MC-IN718 joint achieved the highest ultimate shear strength (233.3 MPa) followed by vacuum brazed S355MC-IN600 joint (230.1 MPa) and HIP S355-IN718 (203.5 MPa), thereby showing that vacuum brazing and HIP can be viable manufacturing methods to fabricate a high-speed ALA-SynRM rotor.

Open-Circuit Fault-Tolerant Control and Topology Switching Strategy of Active Magnetic Bearing Power Electronics Controller

Active magnetic bearing (AMB) technology has been widely used in high-speed electrical machines. Power electronics controller amplifier is an important segment in AMB system. Failure of power electronics device is a common threat to the reliability of AMB amplifier and can cause serious damage. In order to improve the robustness of the amplifier, this article proposes open-circuit fault-tolerant control strategies based on different topologies. For single-axis systems, a pair of windings with a single degree of freedom can work in four different working modes based on the three-phase full-bridge structure. It can detect and locate the open-circuit fault of a power electronics switch in operation. After promotion to multiaxis systems, a novel kind of topology for amplifier with fault tolerant strategy has been proposed that can also detect the open-circuit fault of power electronics switch and switch to fault tolerance mode for a multiaxis system. Fault tolerant experiments verify the feasibility and rapid response of different fault tolerance strategies with an AMB testbed in this article.

Rotor Investigation of High-Speed Permanent Magnet Motor with Roundness Error and CFD-Thermal Distribution Analysis

The rotor overtemperature caused by losses is one of the important issues for the high-speed electrical machine. This paper focuses on the rotor loss analysis and CFD-thermal coupling evaluation for 105 kW, 36,000 r/min HSPMSM. Three types of sleeve materials as carbon-fiber, Titanium alloy, and stainless steel are introduced in this paper, researching the effects of sleeve conductivity, thickness and rotational speed on rotor eddy current loss, balancing rotor mechanical strength. The sleeve made of titanium alloy material with a thickness of 3.5 mm is chosen to effectively suppress the rotor eddy current loss in high-speed motors in the paper. The air friction loss becomes significant based on the PM motor at high rotational speed. The roundness error of the rotor sleeve has the important impact on the air friction loss of the rotor and the rotor temperature of the motor, which leads to the over temperature of the rotor. Therefore, based on the CFD fluid model, the influence of roundness error, cooling parameters, rotational speed and temperature boundary on the air friction loss is studied in detail, and the expression is summarized to provide reference for estimating the air friction loss. According to the rotor structure in this paper, the optimal cooling air inlet velocity is 10 m/s. Finally, the loss separation method is used to obtain the air friction loss measurement results. The accuracy of the finite element calculation results of air friction loss is verified through the experimental data. The temperature rise of the HSPMSM was also measured with 5.5% error. In this paper, the conclusion and analysis method could provide some reference for the research of the rotor structure and the improvement of the efficiency of HSPMMs.

Sensorless Switched Reluctance Machine and Speed Control: A Study to Remove the Position Encoder at High Speed of Operation

High-speed electrical machines have been of great research interest because of their excellent efficiency and high storage capacity. In the case of switched reluctance machines (SRMs), position feedback is required for effective operation. The installation of this sensor in a high-speed flywheel is difficult and expensive. This paper proposes and analyses a methodology to estimate the position of a SRM and remove the position encoder to apply the machine as a flywheel at 50,000 rpm. The machine is modeled with non-linear characteristics, and is simulated under single-pulse operation due to the high-speed. Two configurations of the sensorless method are presented: Robust Method and Sequential Method. The robust configuration identifies the firing angles position only, while the sequential setup can track any position. Both configurations present advantages and disadvantages in relation to the error of estimation and to the number of estimations. The methods are tested in closed-loop speed control. In the two cases, the position estimation supports satisfactory results for simulating operation of the machine at high speed.