This study considers the design of surface-mounted permanent magnet electrical machines for high-speed applications and proposes a methodology to determine the maximum achievable power density. Power density is usually improved by increasing rotational speed. At high speed, a mechanical retaining system for the rotor magnets must be considered. As the speed increases, the thickness of the retaining sleeve becomes larger, reducing torque capability. There will be an optimal speed at which the output power will be maximised. Both structural and electromagnetic design must be considered simultaneously to properly address this design problem. To simplify the design procedure, static finite-element simulations are used for the electromagnetic analysis and analytical formulae are employed for retaining sleeve sizing. The procedure is aided by multi-objective optimisation algorithms. A case study based on the specification of an aeronautical actuator is presented. The performances that can be obtained using different iron cores, high-grade silicon steel, and cobalt iron steel are compared. Finally, results obtained from transient finite-element electromagnetic and structural analysis are presented to validate the feasibility of the proposed procedure.

This study presents an optimisation method for slotless permanent magnet synchronous machines to maximise torque density. The slotless structure with outer rotor and Halbach array has been selected to limit iron losses, torque ripple, cogging torque, and high-order harmonics. High-speed operation compounds both ac copper loss and mechanical stress. The former causes a temperature rise in the machine, while the latter is induced by strong centrifugal forces. A finite-element analysis-based optimisation method that utilises a parallel multistart, mesh adaptive direct search strategy is proposed to consider ac copper loss and mechanical stress as constraint variables. Finally, the torque densities of titanium and aermet shell designs were compared to show how material selection provides a trade-off in terms of torque production, mechanical stress, and weight.

The three degree-of-freedom (3-DOF) hybrid magnetic bearing (HMB) sets radial, axial at one entirety, which can effectively save the bearing installation space. Here, a 3-DOF HMB is designed, optimised, and tested for a 30 kW 60,000 r/min high-speed motor system. The radial and axial bearing capacity is analysed by equivalent magnetic circuit method and three dimensional finite element model (FEM) of initial model of 3-DOF HMB is established. Then, the radial bearing capacity, axial bearing capacity, current-stiffness, and displacement-stiffness are selected as the optimised design target by using chaos particle swarm optimisation algorithm. Meanwhile, the axial length, eddy-current loss, and air-gap flux density are selected as constraints of optimization. The optimal results showed that the axial length is decreased, the eddy-current loss is reduced, and the harmonics in the air gap is lower while the bearing capacity is improved. Furthermore, a 30 kW 60,000 r/min high-speed motor with proposed 3-DOF HMB is manufactured, and the experiments of the radial/axial static bearing capacity test, dynamic performance of high-speed motor with no load in 60,000 r/min and with load in 55,000 r/min are carried out. Experiment results show that the optimised 3-DOF HMB has good force performance and dynamic performance.

A comprehensive description of a bearingless permanent magnet synchronous machine is presented including simulation, design, control and measurement focusing on a 1 kW/60,000 min⁻¹ machine. A combined six-phase winding is used for the excitation of the two-pole motor field wave and the four-pole levitation field wave by applying two parallel three-phase current systems. The decomposition into the individually controllable current systems for motor torque and lateral rotor position control and the calculation of the relevant control parameters is explained. Measurements give an insight on the controlled motor performance. Thus, it is shown that the combination of torque and lateral force production with a single six-phase winding, fed by two three-phase inverters, not only leads to advantages in winding manufacturing but can be operated with a conventional field-oriented control also at high speed.

High-speed permanent magnet motors (HSPMM) have attracted much attention due to the inherent characteristics such as high-power density, small size, small inertia, and high response. HSPMM is a comprehensive and complex system of multidisciplinary cross-coupling such as electromagnetism, structural mechanics, rotor dynamic, fluid mechanics and heat transfer. Therefore, the design of HSPMM requires a multidisciplinary and integrated design approach. In this study, a 20 kW, 20,000 rpm HS interior PMM (HSIPMM) is designed based on multi-physics fields. To reduce the end length of winding, the back round winding type is adopted, compared with the common structure, it is found that the temperature rise of the stator used back round winding type can be reduced by 11.5%. Finally, the superiority of the proposed HSIPMM is proved by the experimental results, and the efficiency of the motor is about 96.1%.

For the high-frequency permanent magnet electrical machine, a reasonable mechanical aspect design is crucial to meet its stability and reliability. This study focuses on the accurate modelling and analysis of the natural frequencies and modes of the rotor assembly for a designed and manufactured 100 kW 32,000 r/min motor. The influence of contact stiffness and friction on bending frequencies is analysed in detail. To obtain the accurate results of first two bending frequencies, on the basis of the finite-element method, the optimisation method is carried out to acquire appropriate variables of the contact stiffness and friction. The optimised results show that the method proposed in this study can realise the accurate analysis of the rotor mode, which are verified by free–free modal testing of the rotor.

This study presents two design methodologies for high-speed synchronous reluctance (REL) machines. The interest for high-speed drives comes from the request for compactness and high efficiency. The synchronous REL motors have been widely studied for several applications, but a coherent design procedure for high speed has not been proposed in the literature. The study proposes some analytical procedures to get an initial design. Then the rotor geometry optimisation through a differential evolution algorithm is described. Finally, a design example is given and thoroughly analysed using these two approaches.

Owing to the definite merits of high-efficiency and high-power density, the permanent-magnet (PM) brushless machines have been dominating the high-performance industrial applications. However, the problems of high PM material cost, fluctuating supply of rare-Earth materials and ineffective PM flux control have hindered the widespread applications of the PM brushless machines. In recent years, many attentions have been shifted to the magnetless candidates, while the focuses are mainly placed on the classical candidates. In this study, an overview of magnetless brushless machines including both the classical and advanced types is presented, with emphasis on their machine topologies, features and performances. In addition, the upcoming trend of these machines is reviewed and discussed.

Depending on its mechanical and thermal advantages, solid rotor induction motors (SRIMs) are widely used in demanding high-speed applications. Since eddy currents are set free in SRIMs, great part of rotor losses is caused by space harmonics created in the air-gap. Rotor losses are increased tremendously in high-speed applications with the remarkable increase in driving frequency. Here, an innovative design representing a novel stator and rotor combination that is not achieved in previous studies is proposed by structural changes to stator to eliminate major effective space harmonics. An unconventional stator slotting pattern and winding distribution is calculated by nature-inspired numerical optimisation techniques while keeping the fundamental winding factor relatively high. An example design where novel concepts are implemented is presented and a comparison is given in terms of important operational quantities with that of a standard SRIM.

This study investigates the usage of a nine-phase induction motor (IM) in internal combustion engine vehicle hybridisation. Aiming to minimise structural changes, the parallel-through-the-road (TTR) hybrid architecture was chosen. First, a real vehicle was experimented on the mobility technology centre Federal University of Minas Gerais (CTM-Universidade Federal de Minas Gerais (UFMG) laboratory) to get its characteristics. After that, this technical information was used to model and simulate on the software advanced vehicle simulator (ADVISOR). The simulated model results were compared with the experimental tests results realised with the vehicle on the tests track and CTM-UFMG. Posteriorly, through a validated vehicle model, a drivetrain powered by a prototype of a nine-phase IM was integrated into the rear axle to do the hybridisation process simulation. To do that some structures modifications were necessary on ADVISOR since this tool does not include the parallel-TTR architecture. Vehicles modelled were simulated using the urban driving dynamometer schedules. Finally, the comparative analyses of simulation results show the improvements in fuel consumption, vehicle efficiency, emission gas, and the nine-phase motor operation in a hybrid TTR.

Surface-mounted permanent magnet (SPM) machines are preferred for high-speed aerospace applications over induction and switched reluctance machines, since they combine the advantages of high torque density and efficiency. Also, in aerospace applications, where low rotor weight and inertia are essential requirements, a permeable hollow shaft is proposed to replace the need for rotor back-iron and reduce the overall rotor weight. For rotor mechanical integrity, a retaining sleeve is commonly used, leading to thicker magnetic airgap. Furthermore, when permeable rotor endcaps are applied, an increase of the magnetic end leakage occurs, i.e. end-effect. In this study, the influence of the rotor endcaps on the mechanical and electromagnetic performance of a high-speed SPM machine is investigated through 3D-finite element analyses. Also, different endcap thickness and different rotor shaft materials are investigated and compared in this work. Finally, a prototype of the SPM machine under study has been manufactured and tested. The comparison between simulation and experimental results is presented and discussed.

Accurate calculation of rotor losses in permanent magnet (PM) synchronous machines can be critical because these losses tend to be very small relative to others in the machine. Numerical methods, such as finite element analysis (FEA), can now provide accurate estimates of these losses, but they, especially 3D-FEA, can be time consuming. Analytical methods therefore remain very useful as quick tools for estimating losses at the early design stages. This study presents a new improved analytical method for the calculations of rotor eddy current losses in PM machines using a reformulation of the current sheet model into transfer matrices to solve Helmholtz's diffusion equation. Such methodology reduces the complexity of the problem significantly, particularly in machines with retaining sleeves, and simplifies the numerical evaluation of the resulting equations. A high-speed PM machine with a retaining sleeve is presented as a case study. The analytical results are verified using FEA.

This study proposes a novel dual stator composite rotor axial flux induction motor (DSCRAFIM) whose solid rotor is coated with copper layers. A novel multi-slice and multi-layer method is developed and applied to analyse the three-dimensional electromagnetic field distribution in DSCRAFIM. In the application of this analytical method, DSCRAFIM is equivalent to a finite set of equal-width and increasing-length double primary composite secondary linear induction motors, whose steel secondary is divided into a finite set of equal-height layers. The surface impedance theory is applied to derive the improved equivalent circuit model (IECM) of DSCRAFIM, which considers the coupling relationship between dual stator windings. The accuracy of this IECM is then verified by both finite-element analysis and experimental test.

On the basis of predecessors, a theory named inverse transient complex inductance vector is proposed for air-gap eccentricity fault diagnosis of interior permanent magnet synchronous motors, and a specific voltage sequence injection method with simple implementation is proposed here. It is a real-time visualised diagnostic approach. A unique fault index is proposed to diagnose eccentricities. The absolute value of the fault index is positively correlated with the total eccentricity degree. Three types of artificial eccentricities and one type of artificial partial demagnetisation are tested. Both simulations and experiments match the proposed theory and diagnostic approach. The approach gives a clear distinction in detecting air-gap eccentricity and partial magnet demagnetisation. It performs best in the low-speed operating condition.

This study presents dynamic demagnetisation investigations of less-rare-earth (LRE) flux switching permanent magnet (LRE-FSPM) motor under three-phase short-circuit (SC) fault. Owing to relatively low coercivity of ferrite PMs, it is necessary to investigate demagnetised risk of LRE PM motors. Actually, motors suffer from larger demagnetising risk under SC faults than normal conditions. Hence, it is essential for LRE PM motors to comprehensively investigate and enhance anti-demagnetisation capability during design stage. Here, by integrating electrical–magnetic field calculation and driving control circuit, dynamic demagnetisation characteristics of the LRE-FSPM motor under SC faults are calculated as an example. To fairly evaluate demagnetisation withstand capability of LRE-FSPM motor, the non-rare-earth (NRE)-FSPM motor is also presented and compared as a referenced motor. Then, the dynamic demagnetisation characteristics of two motors are analysed and compared, including demagnetising d-axis current, operating points, and demagnetised area. It is found that, the proposed LRE-FSPM motor exhibits improved operating points and less demagnetised area, which is only about one-third of that of NRE-FSPM motor. Finally, the demagnetisation calculation results not only verify the validity of dynamic demagnetisation investigation approach, but also prove the reasonability of LRE-FSPM motor, which provide a promising research path for the design of LRE PM motors.

For surface mounted permanent magnet synchronous motor (PMSM), due to the large rotor rotational centrifugal forces, a sleeve is often used to prevent damage to rotor permanent magnets. However, eddy current losses appearing in the sleeve can increase the temperature of surface mounted PMSM. If the rotor heat dissipation condition is poor, high temperature can influence the surface mounted PMSM performance and even result in thermal demagnetisation of the permanent magnets. Thus, a sleeve scheme designed with low eddy current loss is very necessary. In this study, taking a 12.5 kW, 2000 rpm PMSM with 0.2 mm thickness stainless steel sleeve as an example, first, the influences of sleeve thickness on the eddy current loss and temperature field are analysed. Then, sleeve various composition structures of carbon fibre and stainless steel are presented, and the influences of different composition percentages on the eddy current losses and temperature field are analysed in detail, which shows the effectiveness in reducing the eddy current losses and temperature in the rotor. The obtained conclusions can provide useful reference for the design and research of surface mounted PMSM.

Normally, electrical and mechanical systems are designed and analysed in separate domains but, in this study, interactions between electric and mechanical elements are analysed looking for improvement in the performance of electromechanical drivetrains. The work considers a doubly fed induction generator, evaluated with a frequency analysis of the full electromechanical drivetrain developed and applied to identify how tuning gains and system parameters affect the electromechanical interactions. Analytical transfer functions are presented and validated by simulation and test results.

To achieve high-performance sensorless control of permanent magnet motors with non-sinusoidal back electromotive force (EMF), an improved sliding mode observer (SMO) adopting synchronous rotating low-pass filter (SRLPF) is proposed. The SRLPF is utilised to reduce the back-EMF harmonics and extract the fundamental component. Different from the traditional rotor position observer, the proposed observer can calculate the rotor position with the back-EMF fundamental component. Owing to the decrease in the influence of non-sinusoidal back-EMF, the estimated rotor position harmonic ripple error can be greatly reduced. Then, the high estimated accuracy and excellent sensorless control performance can be obtained. In addition, the proposed strategy is easy for implementation. With the comparison between the traditional SMO and the proposed observer, the experiments of the system steady-state error, the speed tracking performance, and the disturbance rejection ability in the speed range from 60 r/min to the rated speed 750 r/min are presented. The validity of the proposed method is conformed.

A magnetohydrodynamic (MHD) thruster is a type of electric motors which does not have mechanical moving parts and directly converts electrical energy into mechanical energy. In this study, the effect of magnetic field intensity and seawater electrical conductivity on the performance of a marine MHD thruster model is investigated using fully three-dimensional numerical simulations. For the first time, all electric, magnetic and fluid flow fields are considered in three dimensions. The effects of seawater electrolysis and end loss are taken into account in all simulations and a simple analytical model is developed to verify the numerical results. It is shown that increasing the magnetic field intensity or the electrical conductivity of the working fluid decreases the electrochemical and ohmic losses of the thruster at a specific velocity. Therefore, a higher efficiency can be achieved at higher magnetic field strengths and higher seawater electrical conductivities. Also, it is revealed the end loss of the channel increases with an increase in the electrical conductivity of the working fluid and decreases with an increase in the magnetic field intensity.

This study proposes a speed estimation scheme for the sensorless-vector-controlled linear induction motor (LIM) drives for medium–low-speed maglev applications, which is composed of two parts: (i) a sliding mode model reference adaptive system observer for speed estimation; and (ii) a parallel secondary resistance online identification for achieving the improvements of the proposed speed estimation scheme performance. The sliding mode observer (SMO) is established on the basis of the state space-vector model of the LIM considering the dynamic end effect. Based on SMO, both speed and secondary resistance estimation algorithms are obtained by utilising Popov's hyperstability theory. Moreover, the Lyapunov stability theory is adopted for the stability analysis of the proposed speed estimation scheme. The effectiveness of the proposed speed estimation algorithm has been verified and compared with the performance of the conventional speed estimation scheme based on single-manifold SMO by the simulation and hardware-in-the-loop tests.

This study investigates the accurate modelling and the modal natural frequencies of the stator system of a permanent magnet synchronous motor with concentrated winding used in the in-wheel motor system of the electric vehicle. The equivalent material physical properties of each component in the stator system are determined by the correction formula and the empirical coefficient. Meanwhile, the contact conditions between each component are also analysed. According to the structural analysis of stator system, different equivalent finite-element models of winding and frame, together with their effects on the accuracy of simulation results, have been built and investigated, respectively. In addition, the prototype of the motor is fabricated; then the experimental modal analysis of the stator system and its subassemblies are carried out during the manufacturing process. Through comparisons of the results between experiments and finite element anaysis (FEA), the final model of the stator system is determined and verified to be of high accuracy to predict the vibration behaviours of the investigated motor with concentrated winding. Finally, several factors influencing the modal frequencies of stator system are analysed, which could provide certain reference value to the structural design of stator system.