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Abstract This article presents a new rotor with fractional slot distribution winding permanent magnet (FSDWPM) machine to improve the torque density of in‐wheel motor. In order to achieve the high torque/power density and reduced material weight with constrained rotor inner diameter and stator outer diameter, three traditional rotor topologies, including single‐layer V‐shaped, double‐layer V‐shaped, and delta‐type, are selected and compared with the proposed FSDWPM machine. Subsequently, the corresponding basic electromagnetic performances, including open‐circuit back‐EMFs, on‐load torque, and efficiency distributions, of the four machines are investigated and compared by finite element (FE) analysis. The simulated results shows that the proposed rotor arrangement exhibits the highest average torque, excellent field‐weakening capability, the largest high‐efficiency region compared with conventional rotor structures. Finally, a 50 kW FSDWPM machine prototype with double‐layer PM arrangement is manufactured, and some experimental results are conducted to confirm the feasibility and effectiveness of the proposed design.

Abstract A permanent magnet synchronous machine (PMSM) temperature estimation method fusing the classic lumped‐parameter thermal network (LPTN) and the stator sensor temperature information is investigated. With respect to the industrial servo applications, it is important to monitor the rotor magnet temperature to extend the machine thermal utilisation. A simple LPTN is developed and the quadratic programming is applied to identify the model parameters. The research work shows that the rotor temperature is sensitive to the rotor speed even at low speeds, and this simple estimation network can provide an accurate estimation. The winding sensor information can further improve the performance. A compound mechanism is built, by which the winding temperature estimation error is used as feedback to suppress the model‐based temperature estimation error accumulation. The estimation performance is compared with a regular constant LPTN‐based method. Experimental results based on a PMSM are presented to validate the proposed method.

Abstract The influences of slot/pole number combinations on electromagnetic performances, including flux linkage, inductance, and torque ripple harmonic components etc., resulting from unbalanced characteristics between north and south poles in concentrated winding permanent magnet (PM) machines with symmetrical and asymmetric rotor pole shaping methods are theoretically analysed and experimentally validated in this paper. It shows that for the PM machines with odd number of coils per phase per submachine, including consequent pole (CP) and surface‐mounted PM (SPM) machines, the influences of unbalanced pole characteristics can lead to additional torque ripple harmonics due to additive effects in windings, but can be cancelled in other machines. Compared with symmetrical pole shaping method, asymmetric pole shaping method can result in lower torque ripple for CPPM machines with odd number of coils per phase per submachine, while symmetrical and asymmetric pole shapes have similar effects on torque ripple reduction for other CPPM machines and all the SPM machines. The findings have been validated by finite element analyses on 12‐slot/8‐pole, 12‐slot/10‐pole, 9‐slot/6‐pole, and 12‐slot/14‐pole machines, and by experiments with 12‐slot/8‐pole and 12‐slot/10‐pole CPPM prototypes.

Abstract Electric machines are widely employed in a variety of sectors, including automotive and aerospace industry. With the rising trend towards electrification in aviation, electric machines with increased power density and efficiency are becoming key enabling technologies, requiring the development of innovative design procedures. In this study, a preliminary design procedure for Surface Mounted Permanent Magnet Synchronous Machines (SPMSMs) intensively cooled by means of oil channels placed in the stator slots is proposed. The analytical derivation of SPMSM sizing equations, including the sub‐domain model and optimisation algorithm will be reported in detail. Indeed, both the electromagnetic and thermal equations of the machine are considered for the derivation of the sizing tool. As a result, the latter allows to capture variation of the machine design not only in terms of mechanical demands, such as power and speed, but also in terms of coolant characteristics, and can be effectively employed to perform trade‐off studies at a preliminary design stage. The proposed design tool will be used for a specific case study: The design of a high‐speed machine for an aerospace hydraulic actuator. The accuracy of the proposed design tool is validated for different parameters by comparing the results to experimental measurements performed on an existing 8‐pole 9‐slot prototype SPMSM.

Abstract This article proposes an equivalent magnetic network (EMN) model to improve the accuracy of electromagnetic analysis, where a modular modelling of hybrid cross‐shaped mesh (CS‐M) elements is introduced. By applying hybrid CS‐M elements, the modelling of air gap and its surrounding regions is regulated into an identical width. As a result, the relative motion of the motor is simpler to simulate by changing the nodal connection without involving the non‐linear permeance. The airgap flux density is solved more accurately than the regular CS‐M elements as well. A 12‐slot/10‐pole ferrite permanent magnet (FPM) motor with assisted poles of unequal pole‐arc ratios is selected as an example to be built with the proposed EMN model. After solving the EMN model, the effectiveness and accuracy of the proposed EMN model are verified by comparing it with the FEA model and experiments. Additionally, based on the frozen permeability (FP) method, transient torque components can be separated accurately with a transient torque solution related to virtual work principle (VWP) for the EMN model.

Abstract This paper investigates the unbalanced magnetic force (UMF) produced by angular eccentricity in a magnetic screw. The principle of eccentricity is briefly outlined and an analytical expression that can be used to predict UMF of a magnetic screw is established. A 3D magnetic screw model with helically magnetized permanent magnets (PM) has been built and simulated in ANSYS Maxwell with different angular eccentricities. Comparing the finite elements (FE) simulation and analytical calculation results, there is a certain difference in the UMF of the magnetic screw, which is also caused by the asymmetry of the magnetic screw structure. It has been shown that compared to the linear tubular PM motor with the same thrust force capability, the magnetic screw has a much small UMF, which greatly simplifies the mechanical design of the magnetic screw.

In this article, a hybrid analytical model for a quasi‐regular polygon rotor (QPR) is proposed. It mainly uses the subdomain method and conformal mapping to solve a non‐circular boundary in the QPR. Firstly, the subdomain method combined with an equivalent surface current method is used to calculate the air‐gap magnetic field considering a slotted stator with a circular rotor. Secondly, by segmenting the non‐circular boundary in the QPR, the complex relative air‐gap permeance of the QPR can be calculated using the conformal mapping. Thirdly, this complex relative air‐gap permeance modifies the air‐gap magnetic field calculated in the first step to obtain the actual magnetic field distributions. Consequently, no‐load and loaded air‐gap flux densities, back‐electromotive force and torque can be obtained. A 12‐pole/3‐phase permanent magnet motor is modelled using the proposed hybrid analytical model, which is validated by finite‐element analysis and experiment. This proposed hybrid analytical model presents a new way of processing the QPR. Its calculation speed is nearly 50 times faster than the finite‐element analysis, which is of great help to the initial design and optimisation of machines with QPRs. [ABSTRACT FROM AUTHOR]

The contra‐rotating machine (CRM) has been a preferable selection of the contra‐rotating propulsion system (CRPS) owing to its high efficiency, high compactness, and low noise. However, the conventional CRM with rotating stator has the problem of brush and slip ring, and the conventional brushless CRM has the problem of coordinated control of equal and opposite torque. Aiming at the above problems, this article proposes a transverse‐dislocated magnetic‐field modulated brushless contra‐rotating machine (TDMFM‐BCRM). The proposed TDMFM‐BCRM has some advantages of no rotating winding, no associated brushes and slip rings, and equal and opposite torques at any time, therefore it has good potential for the CRPS. The working principle of the TDMFM‐BCRM including three dimensional magnetic‐field modulated theory, back electromotive force (EMF) generation, and torque relation is studied. Then, the influences of main parameters including magnetic block parameters and PM sizes on torques are investigated. The critical electromagnetic performances of the TDMFM‐BCRM are analysed. A prototype of TDMFM‐BCRM is manufactured and measured to validate the above analysis. Finally, the comparison of the TDMFM‐BCRM and the existing schemes are analysed. [ABSTRACT FROM AUTHOR]

A multi‐phase permanent magnet synchronous motor (PMSM) with fractional‐slot windings is proposed to reduce electromagnetic vibration and improve torque performance. Firstly, the analytical expression of electromagnetic force is derived, and the stator teeth modulation effect of electromagnetic force is introduced. The spatial order of the electromagnetic force and the stator teeth modulation are closely related to the slot‐pole combination of the PMSM. Then, three PMSMs with different slot‐pole combinations are presented, and they represent fractional‐slot concentrated winding, integral‐slot distributed winding and fractional‐slot distributed winding, respectively. Their torque performance and electromagnetic vibration performance are studied and compared considering stator teeth modulation. In addition, the multi‐phase winding technology is adopted to further improve the torque performance of the proposed PMSM. Finally, a 90s20p PMSM is manufactured, and the finite element method and experimental method are used to verify the proposed low vibration design method. [ABSTRACT FROM AUTHOR]

This article presents a novel method for fastly obtaining orthotropic material parameters in permanent magnet synchronous motor. First, a theoretical model of the equivalent single cylindrical shell is introduced with three orthotropic material parameters by considering the orthotropic characteristics of the motor. Then, the relationship of three orthotropic material parameters and the axial mode order m, the radial mode order n and modal frequency f is established. On this basis, an analytical method with m = 0 is proposed to acquire three values, and its adaptability is pointed out. Meanwhile, based on the above obtained orthotropic material parameters, the calculation method of modal frequencies is presented. Finally, the modal test and finite‐element method are implemented to verify the rationality of the proposed method. [ABSTRACT FROM AUTHOR]

A general analytical model is developed in a concise block matrix form for surface‐mounted permanent magnet (SPM) machines with series‐parallel coil connections under inter‐turn short circuit (ITSC) fault. In the model, branch currents are used as state variables and inductances of different series‐parallel coil connections are calculated using an analytical method, namely winding function approach (WFA) together with slot permeance method. Based on the characteristics of the calculated inductances and the developed fault model, the multiphase Clarke transformation has been proposed to simplify the fault model. In the process of model simplification, the healthy machine model using branch currents as state variables have been proven to be equivalent to that using 3‐phase currents as state variables. The proposed fault models of a 3kW 96‐slot 32‐pole SPM machine with different series‐parallel coil connections have been built in Matlab/Simulink and validated by time‐stepping 2D FE simulations. Simulation results show that different series‐parallel coil connections have little influence on the amplitude of the ITSC current. Finally, a small scale 24‐slot 8‐pole SPM machine prototype has been built to further validate the accuracy of the proposed fault model. [ABSTRACT FROM AUTHOR]

Recently the new topologies of the permanent magnet (PM) motor attract a lot of attention. These newly introduced PM motors are not mature in design aspects and suffer from different perspectives. Therefore, it is necessary to develop a common design procedure to overcome these drawbacks. One of the common problems with newly introduced PM motors is the phenomenon of irreversible demagnetisation (ID) at high temperatures. So, a solution to this problem will be presented. The recently introduced ring winding axial flux PM (RWAFPM) motor is considered as a case study. First, a modified approach for modelling ID is introduced. Then, the effect of rotor geometry parameters on the ID of the RWAFPM motor is discussed. Finally, developed multi‐level multi‐objective design optimisation considering ID is presented based on the developed Taguchi method. [ABSTRACT FROM AUTHOR]

In the context of a collaboration between the Medical University of Vienna, the Power Electronic Systems Laboratory of ETH Zurich, and Charité Berlin, the novel implantable total artificial heart ShuttlePump is currently being developed. Its novel low-complexity pumping concept requires a compact linear–rotary actuator (LiRA). The linear actuator (LA) part was designed, realized, and experimentally verified in previous work, and it can provide a peak axial force of about 45 N with about 8 W of continuous power dissipation. This article presents the details of the rotary actuator (RA) part. This has considerably lower output power requirements (about 100 mW) due to the low operating torque and angular speed (3.1 mN$\cdot$m and up to 300 r/min, respectively). However, the RA is highly constrained spatially, as it needs to be integrated very close to the previously realized LA. This forces a permanent magnet synchronous machine (PMSM) design with a rotor only partially equipped with permanent magnets and stators covering only half of the total circumference, which introduces a considerable cogging component to the total torque. The proposed PMSM is, hence, optimized using finite-element method simulations to select a final design with low power losses and low cogging-induced angular speed ripple. The machine is realized as a hardware prototype, and the experimental measurements confirm that the proposed RA can meet the continuous torque requirement with 324 mW of power losses. The successful implementation of the RA (and LA) finally verifies the practical feasibility of the integrated LiRA and provides the basis for a comprehensive test of the complete ShuttlePump in a hydraulic test rig in the course of further research.

This paper investigates the unbalanced magnetic force (UMF) produced by angular eccentricity in a magnetic screw. The principle of eccentricity is briefly outlined and an analytical expression that can be used to predict UMF of a magnetic screw is established. A 3D magnetic screw model with helically magnetized permanent magnets (PM) has been built and simulated in ANSYS Maxwell with different angular eccentricities. Comparing the finite elements (FE) simulation and analytical calculation results, there is a certain difference in the UMF of the magnetic screw, which is also caused by the asymmetry of the magnetic screw structure. It has been shown that compared to the linear tubular PM motor with the same thrust force capability, the magnetic screw has a much small UMF, which greatly simplifies the mechanical design of the magnetic screw. [ABSTRACT FROM AUTHOR]

The potential of wind energy resources is propelled fast and power extraction is increasing considerably due to the development of reliable and cost-effective wind turbine generators. Various permanent magnet (PM) wind generators have been implemented for wind power generation, among which, the conventional transverse-flux permanent magnet generator (TFPMG) is popular due to their higher torque density and simple coil design, but it has some disadvantages in comparison with radial flux PM generator, i.e., higher flux leakages and complex 3D flux pattern. In this article, a fall-back inner rotor transverse-flux PM wind generator FB-TFPMG has been investigated to override the disadvantages of conventional TFPMG. It employs half of the total PMs on the rotor and U-shaped stator cores. An analytical model of the proposed FB-TFPMG has derived using magnetic equivalent reluctance circuit (MERC) to predict the performance of the generator, i.e., flux densities in the air-gap, under aligned and unaligned conditions of rotor PMs with U-shaped stator cores. The results of the MERC model is verified with the results obtained through 3D finite element analysis. [ABSTRACT FROM AUTHOR]

This article presents a new rotor with fractional slot distribution winding permanent magnet (FSDWPM) machine to improve the torque density of in‐wheel motor. In order to achieve the high torque/power density and reduced material weight with constrained rotor inner diameter and stator outer diameter, three traditional rotor topologies, including single‐layer V‐shaped, double‐layer V‐shaped, and delta‐type, are selected and compared with the proposed FSDWPM machine. Subsequently, the corresponding basic electromagnetic performances, including open‐circuit back‐EMFs, on‐load torque, and efficiency distributions, of the four machines are investigated and compared by finite element (FE) analysis. The simulated results shows that the proposed rotor arrangement exhibits the highest average torque, excellent field‐weakening capability, the largest high‐efficiency region compared with conventional rotor structures. Finally, a 50 kW FSDWPM machine prototype with double‐layer PM arrangement is manufactured, and some experimental results are conducted to confirm the feasibility and effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

The article describes a new approach to line start permanent magnet synchronous motors (LSPMSM) design process. This different, novel approach is based on the modification of mass-produced induction motors. The presented method facilitates and expedites the electrical motor design process. A field-circuit model of the motor has been created to expound the methodology of the process. Then, the machine's geometry was changed to apply permanent magnets. The problems and benefits associated with the use of permanent magnets were described. The created model was tested. The authors examined the operation of the LSPMSM motor in different states, such as starting, no-load, and blocked-rotor tests. Electromechanical characteristics have been plotted. The simulation results were compared with the parameters and characteristics of the induction motor. The conducted tests proved the correctness of the design process. The operational properties of the motor have been improved. Moreover, the validity of using LSPMSM motors instead of induction motors has also been demonstrated. [ABSTRACT FROM AUTHOR]

A permanent magnet synchronous machine (PMSM) temperature estimation method fusing the classic lumped‐parameter thermal network (LPTN) and the stator sensor temperature information is investigated. With respect to the industrial servo applications, it is important to monitor the rotor magnet temperature to extend the machine thermal utilisation. A simple LPTN is developed and the quadratic programming is applied to identify the model parameters. The research work shows that the rotor temperature is sensitive to the rotor speed even at low speeds, and this simple estimation network can provide an accurate estimation. The winding sensor information can further improve the performance. A compound mechanism is built, by which the winding temperature estimation error is used as feedback to suppress the model‐based temperature estimation error accumulation. The estimation performance is compared with a regular constant LPTN‐based method. Experimental results based on a PMSM are presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

The influences of slot/pole number combinations on electromagnetic performances, including flux linkage, inductance, and torque ripple harmonic components etc., resulting from unbalanced characteristics between north and south poles in concentrated winding permanent magnet (PM) machines with symmetrical and asymmetric rotor pole shaping methods are theoretically analysed and experimentally validated in this paper. It shows that for the PM machines with odd number of coils per phase per submachine, including consequent pole (CP) and surface‐mounted PM (SPM) machines, the influences of unbalanced pole characteristics can lead to additional torque ripple harmonics due to additive effects in windings, but can be cancelled in other machines. Compared with symmetrical pole shaping method, asymmetric pole shaping method can result in lower torque ripple for CPPM machines with odd number of coils per phase per submachine, while symmetrical and asymmetric pole shapes have similar effects on torque ripple reduction for other CPPM machines and all the SPM machines. The findings have been validated by finite element analyses on 12‐slot/8‐pole, 12‐slot/10‐pole, 9‐slot/6‐pole, and 12‐slot/14‐pole machines, and by experiments with 12‐slot/8‐pole and 12‐slot/10‐pole CPPM prototypes. [ABSTRACT FROM AUTHOR]

This paper presents an analytical study of the air-gap magnetic field of a Surface Permanent Magnet (SPM) linear machine under no load. By means of the method of images, the complex expression of the magnetic field of a conductor, inside the air gap between two smooth iron surfaces, is retrieved. Then, integrating the conductor expression, the formulation of the magnetic field of a current sheet and thus the one of a SPM, using two vertical current sheets, is obtained. At last, the no-load magnetic field expression, for a generic time instant, of a slotless machine is retrieved. The novelty of the proposed approach is the availability, due to a different calculation approach, of a unique closed-form formulation for the slotless machine air-gap field, a quantity that, in literature, is usually present in Fourier series formulation. Additionally, as a means to calculate integral quantities and show the goodness of the method a complex slotting function is introduced to account for the slotted geometry. Finally, starting from Lorenz's force formulation, the expression of the Maxwell tensor in complex form is retrieved and the contribution of forces, integral of the complex stress tensor quantity, will be calculated and compared with FEM simulations, showing a good agreement also with the analytical slotted model. [ABSTRACT FROM AUTHOR]

This article proposes an equivalent magnetic network (EMN) model to improve the accuracy of electromagnetic analysis, where a modular modelling of hybrid cross‐shaped mesh (CS‐M) elements is introduced. By applying hybrid CS‐M elements, the modelling of air gap and its surrounding regions is regulated into an identical width. As a result, the relative motion of the motor is simpler to simulate by changing the nodal connection without involving the non‐linear permeance. The airgap flux density is solved more accurately than the regular CS‐M elements as well. A 12‐slot/10‐pole ferrite permanent magnet (FPM) motor with assisted poles of unequal pole‐arc ratios is selected as an example to be built with the proposed EMN model. After solving the EMN model, the effectiveness and accuracy of the proposed EMN model are verified by comparing it with the FEA model and experiments. Additionally, based on the frozen permeability (FP) method, transient torque components can be separated accurately with a transient torque solution related to virtual work principle (VWP) for the EMN model. [ABSTRACT FROM AUTHOR]

Electric machines are widely employed in a variety of sectors, including automotive and aerospace industry. With the rising trend towards electrification in aviation, electric machines with increased power density and efficiency are becoming key enabling technologies, requiring the development of innovative design procedures. In this study, a preliminary design procedure for Surface Mounted Permanent Magnet Synchronous Machines (SPMSMs) intensively cooled by means of oil channels placed in the stator slots is proposed. The analytical derivation of SPMSM sizing equations, including the sub‐domain model and optimisation algorithm will be reported in detail. Indeed, both the electromagnetic and thermal equations of the machine are considered for the derivation of the sizing tool. As a result, the latter allows to capture variation of the machine design not only in terms of mechanical demands, such as power and speed, but also in terms of coolant characteristics, and can be effectively employed to perform trade‐off studies at a preliminary design stage. The proposed design tool will be used for a specific case study: The design of a high‐speed machine for an aerospace hydraulic actuator. The accuracy of the proposed design tool is validated for different parameters by comparing the results to experimental measurements performed on an existing 8‐pole 9‐slot prototype SPMSM. [ABSTRACT FROM AUTHOR]

The three-dimensional(3D) analytical model of the magnetic field in an Axial Flux Permanent Magnets Maglev Motor(AFPMMM) is proposed and investigated the influence of the structural parameters on electromagnetic characteristics. Firstly, the topology and working principle of the AFPMMM is introduced, and the model is transferred into a mathematical model in 3D cartesian coordinate. Then, the volume integral method and equivalent current sheets model is applied to find the 3D magnetic field distribution function of Halbach rotor. A unified form expression can be obtained by two dimensional discrete fourier transform (2-D DFT) is applied on the 3D magnetic field distribution function. Thirdly, the conductive and nonconductive regions of AFPMMM will be formulated by the second order vector potential (SOVP) to built the 3D analytic model. The expression of the lift force, torque and power losses was derived. Besides, the relationship between electromagnetic characteristics and structural parameters of the AFPMMM were analyzed based on 3D analytic model and validated using the 3D finite element analysis(FEA). Finally, the experiments based on a small scale prototype are carried out to verify the analytical results.

Accurate modeling of motor magnetic fields facilitates all aspects of motor analysis, design, and optimization. Existing methods are difficult to balance the speed and accuracy of modeling, among which the widely popular finite element method is relatively time-consuming and the accuracy of magnetic circuit modeling is difficult to guarantee. In this regard, this paper presents a magnetic equivalent circuit model based on the multiple flux source network for interior permanent magnet (IPM) machines. The model considers the magnetic saturation effect through a non-linear iterative process. The accuracy improvement of the proposed model has been verified by comparison with the traditional single-flux-source model. Furthermore, the proposed model greatly saves the calculation time while bringing fairly good accuracy compared to the finite-element method, which is beneficial for the design optimization of the IPM machines.

Permanent magnet synchronous generators (PMSGs) with high output density per unit volume are becoming widespread in wind-power generation systems. Among them, spoke-type PMSGs are more challenging to magnetize than other PMSGs, owing to their structural characteristics. Magnetization performance is critical because it is directly related to the demagnetization and mass productivity of permanent magnets, and load performance is reduced when non-magnetization occurs due to the low magnetization performance. Additionally, the starting performance is crucial in wind turbines and is influenced by the cogging torque of the PMSG. This is because starting a wind turbine with a large cogging torque is more challenging. Therefore, this study proposes a spoke-type PMSG rotor shape design for low capacity wind turbines that considers magnetization and cogging torques. We analyzed the principle of magnetization and the factors influencing magnetization performance, and designed a rotor shape with improved magnetization performance. Additionally, we applied an asymmetric rotor barrier structure to reduce the cogging torque and analyze the performance of the final model using finite element analysis. We analyzed the temperature saturation during the operation of the final model using a thermal network method and validated the irreversible demagnetization accordingly. [ABSTRACT FROM AUTHOR]

Fault diagnosis techniques applied to synchronous motors such as Permanent Magnet Synchronous Machines (PMSMs) and Synchronous Reluctance Machines (SynRMs) are scarcely addressed in the literature, in strong contrast to the attention paid to asynchronous motors. In addition, the most widespread techniques are those based on steady-state condition analysis, and little attention is paid to detection during transient operation. The present paper aims to identify research gaps on the topic and to demonstrate the potential of transient analysis. First, the different diagnostic methodologies in literature are thoroughly analyzed. Then, two laboratory case studies are presented to demonstrate the potential of fault detection under non-stationary conditions for a PMSM and a SynRM. Stator current analysis is performed by building time–frequency maps to analyze the evolution of different fault indicators. The results show clear differences between healthy and faulty conditions during the transient regime. [ABSTRACT FROM AUTHOR]

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.

Abstract A modular motor drive (MMD) can be considered as a multi‐agent system, in which the agents work together to reach a common goal. One agent in such an MMD comprises only a subset of the concentrated windings and power electronic converter modules and is equipped with an independent controller. The goal of this research is to let the agents cooperate to distribute a torque demand among them in a completely decentralised way, in order to comply with the flexibility and reliability of modular motor drives. However, the current condition of each agent must still be taken into account during this torque allocation. To limit the communication load, only communication between neighbouring agents is allowed. The combination of a gossip consensus algorithm and multiple decentralised PI current controllers is used for this purpose. Simulations and experimental results on a modular axial‐flux permanent magnet synchronous machine consisting of five agents confirm that the total torque demand is delivered under the proposed control strategy, even during agent malfunctions, under random communication link failures and with non‐identical agents.

Abstract In the field of a model predictive control of a permanent magnet synchronous motor (PMSM), the predictive flux control (PFC) has received great attention, which only takes the stator flux vector as the control variable instead of the electromagnetic torque and the stator flux amplitude. Because PFC does not involve the cumbersome setting of weight factors, it is a promising control algorithm. However, the prediction of the stator flux vector depends on motor parameters, which inevitably reduces the robustness of the control system. In order to solve this problem, this paper proposes a hybrid flux predictor‐based predictive flux control of PMSM drives. The proposed stator flux predictor combines the voltage prediction model and the current prediction model, and the proportional–integral regulator is utilised to control the switching between the two prediction models. Experimental results show that the proposed algorithm has better dynamic, steady‐state and robust performances than the traditional predictive flux control.

In this study, the electromagnetic performances of dual 3‐phase permanent magnet (PM) machines with coil span of two slot‐pitches are comparatively investigated. It mainly focuses on two PM machines with different slot/pole number combinations (Ns/2p), that is, the 24‐slot/10‐pole and 24‐slot/14‐pole machines (2p = Ns/2 ± 2). First, winding configurations are illustrated for these two dual 3‐phase machines with 30° angle displacement. Then, the winding factor, back electromotive force, average torque, torque ripple, iron and PM losses, short‐circuit (SC) current, and PM irreversible demagnetisation are analysed and compared for both machines on the conditions of healthy operation and one set of three‐phase fault, that is, SC or open circuit (OC), respectively. The comparative results show that on healthy condition the 14‐pole PM machine has a slightly larger torque output. Besides, on 3‐phase OC condition, the 14‐pole machine also performs better over‐rating torque capability. In terms of iron and PM losses, the 10‐pole machine has smaller iron losses but larger PM losses than the 14‐pole machine. Moreover, on 3‐phase SC condition, the 14‐pole machine has a significantly lower risk of PM irreversible demagnetisation than the 10‐pole machine, although both machines have very similar SC currents. Finally, the 24‐slot/10‐ and 14‐pole dual 3‐phase PM machines are both prototyped and some tests are carried out for validation. [ABSTRACT FROM AUTHOR]

This article presents a novel doubly salient permanent magnet (DSPM) machine with enhanced torque performance. The key is that an assistive magnetic flux is produced by using two sets of slot PMs inserted into the slot openings, which can effectively improve the torque production. Besides, a complementary magnetic path is built by dual rotors with 180° angle shift to reduce leakage flux, which can effectively suppress the torque ripple. In this article, the proposed machine design is presented, including working principle, winding configuration, magnetic path analysis. Then, the Genetic Algorithm is used to find the optimal designs for the proposed machine. Further, to verify the effectiveness of the proposed machine, three doubly salient machines are compared, including the proposed machine, a DSPM machine without assistive slot PM design, and a dual-rotor DSPM machine without complementary rotor structure. Finally, a prototype of the proposed machine is built and tested to verify the validity of the proposed machine design. [ABSTRACT FROM AUTHOR]

In this article, a new zero-sequence current suppression technique for electrical machine emulators with reduced component count is proposed. The proposed control scheme is implemented by properly regulating the zero states in space vector modulation (SVM). It is well known that a machine emulator allows fast experimental validation of the control and design of a drive system without having a physical electrical machine, since the machine is replaced by another voltage-source converter and a three-phase inductor. However, in emulators with a coupled dc link, circulating zero-sequence current is freely developed creating additional load for the power switches. The currently available control methods require additional hardware common-mode filters to effectively reduce this current. Contrarily, the proposed SVM algorithm suppresses the zero-sequence current more effectively via direct compensation of common-mode voltage, and thus, no additional hardware filters are needed. Thus, an electrical machine emulator with less hardware requirements can be developed with the proposed control technique for being utilized in several laboratory test-bench applications. Experimental results on a 60-kW system validate the effectiveness of the proposed SVM algorithm, since the zero-sequence current amplitude has been measured to be 3.7% of the phase current or even less than this. [ABSTRACT FROM AUTHOR]

Exoskeletons are powerful tools for aiding humans with pathological conditions, in dangerous environments or in manually exhausting tasks. Typically, they are designed for specific maximum scenarios without taking into account the diversity of tasks and the individuality of the user. To address this discrepancy, a framework was developed for personalizing an exoskeleton by scaling the components, especially the electrical machine, based on different simulated human muscle forces. The main idea was to scale a numerical arm model based on body mass and height to predict different movements representing both manual labor and daily activities. The predicted torques necessary to produce these movements were then used to generate a load/performance cycle for the power unit design. Considering these torques, main operation points of this load cycle were defined and a reference power unit was scaled and optimized. Therefore, a scalability model for an electrical machine is introduced. This individual adaptation and scaling of the power unit for different users leads to a better performance and a lighter design. [ABSTRACT FROM AUTHOR]

Abstract A fast hybrid analytical model is presented to predict the on‐load performance of double‐layer interior permanent‐magnet synchronous machines (IPMSMs) considering both iron bridges saturation and slotting effects. The saturation of the iron bridges is defined by a constant flux in the magnetic equivalent circuit method. The slotting effect is defined by a flux path function and virtual surface currents (VSCs) in one‐dimensional (1‐D) and two‐dimensional (2‐D) analytical methods, respectively. For the no‐load condition, double‐layer IPMSMs are modelled via surface‐mounted permanent magnet synchronous machines with two types of the permanent magnet model and the Magnetic Islands method are used to calculate the armature reaction. The effect of the stator slots is considered by using VSCs. To increase the computation speed in the 2‐D analytical method, the amount of VSC is calculated by 1‐D analysis. The 1‐D and 2‐D analytical results for a double‐layer IPMSM are compared with those of finite element analysis and experimental set‐up.

Switched Flux Permanent Magnet Machine (SFPMM) encompass unique features of conventional direct current machine, permanent magnet (PM) synchronous machine and switch reluctance machine therefore, applicable for high-speed applications. However, conventional SFPMM exhibits demerits of high PM volume $(V_{PM})$ , high torque ripples $(T_{rip})$ , higher cogging torque $(T_{cog})$ , lower torque density $(T_{den})$ and significant stator flux leakage. In this paper, a new topology of consequent pole (CP) SFPMM (CPSFPMM) is proposed having partitioned PM that improved flux modulation phenomena utilizing flux barriers. Moreover, due to non-linear behaviour of PM and complex stator structure alternate analytical sub-domain model is utilizes for initial design. However, initial design offers lower open-circuit phase flux linkage $(\Phi)$ , average mechanical torque $(T_{avg})$ and $T_{den}$ . Aforementioned electromagnetic key performance indicator with $T_{cog}$ , $T_{rip}$ , total harmonics distortion in $\Phi $ ( $\Phi _{THD}$ ), average power $(P_{avg})$ and power density $(P_{den})$ are refined utilizing Geometric-Based Deterministic Optimization (GBDO). Analysis reveals that proposed new topology of CPSFPMM with flux barriers reduces $T_{cog}$ by 34.90%, $T_{rip}$ by 20.27%, $\Phi _{THD}$ by 28.08% whereas it enhanced $P_{avg}$ by 17.79%, $T_{den}$ and $P_{den}$ by 34.38%.

Permanent Magnet Linear Flux Switching Machines (PMLFSMs) are potential candidates when higher thrust force ( $\boldsymbol {T}_{ \boldsymbol {F}}$ ) and low cost are the primal requirements. However, conventional PMLFSMs shows flux leakages and utilizes high Permanent Magnet (PM) volume ( $\boldsymbol {V}_{ \boldsymbol {PM}}$ ) that increase overall expense. Therefore, this paper proposed novel Segmented PM Consequent Pole Linear Flux Switching Machine (SPMCPLFSM) with flux bridges. In comparison with PMLFSM, the proposed SPMCPLFSM diminish detent force by $\boldsymbol {20.41\%}$ , suppress thrust force ripples by 27.68%, reduces ripple ratio by 1.77 times, improve $\boldsymbol {T}_{ \boldsymbol {F}}$ to 2 times and boost $\boldsymbol {T}_{ \boldsymbol {F}}$ density to 2.64 times utilizing 75% PM volume and reducing PM cost by 24.16%. Moreover, to overcome computational complexity and computation time, analytical model uniting Lumped Parametric Magnetic Equivalent Circuits, vector potential and Maxwell Stress Tensor method are utilized for open circuit flux linkages, magnetic flux density, detent force and thrust force. Finally, analytical model is validated with finite element analysis (FEA) that show good agreement with FEA. Thus, authors are assured to suggest analytical techniques for early design purpose and proposed SPMCPLFSM for roller coaster application.

Permanent magnet synchronous motors (PMSMs) are increasingly used in industrial drive applications. However, these motors can also undergo various failures, causing production line downtime and resulting in economic loss. Modern diagnostic systems allow the analysis of technical conditions based on a dataset containing fault symptoms. In most cases, the development of diagnostic patterns indicates the necessity for interference in motor mechanical construction. This fact speaks to the use of mathematical models, particularly those based on finite-element methods. This study investigated the possibility of fault classification using self-organizing Kohonen maps and a multilayer perceptron, based on training with data from a field-circuit model. The objective of this study is to demonstrate that such neural systems can detect and classify real motor faults under different operating conditions. Research has focused on stator-winding faults, demagnetization, and mixed faults. Experimental tests demonstrated the impressive diagnostic capability of the shallow neural networks developed for diagnostic tasks.

For applications with high torque demand, gearboxes are commonly used to convert torque and speed in order to receive higher specific values for torque and power. This causes additional losses, cost, inaccuracies, effort, and noise. Eliminating the need of a mechanical gear and the associated disadvantages, Transverse Flux Machines with their high torque density are a very promising alternative. Despite a high torque density and a high efficiency, these types of machines are not commonly used. Due to the complex structure, challenges with mechanical design, and modeling of the machine behavior arise. Additionally, there are high requirements for the inverter due to the low power factor. This paper provides an overview of the state of the art including the potentials and advantages but also the problems and hindrances of these types of machines. Relating to linear and rotary machines from research and industry, the machine is introduced with its history, application and classification. Further, the general technical aspects, the influence of materials for flux guidance, the methods of modeling, methods for a minimization of torque ripples, as well as methods for power factor improvement are presented.

Abstract High‐speed permanent magnetic machine (HSPMM) is attracting more attention due to its high power density, compact size, small rotating inertia, and rapid response capability. However, the design of the HSPMM rotor is a non‐linear, multi‐physics coupled process that makes it difficult to build an accurate mathematical model for optimisation. This study proposes a multi‐objective optimisation method based on the multi‐physics surrogate model (MPSM). This method uses an MPSM to replace the finite element model (FEM) for optimisation, which can effectively solve the problem of non‐convergence and time consumption of the traditional FEM in the optimisation process. Finally, a 1.1 MW, 18,000 r/min HSPMM is produced and related experiments are carried out; the feasibility of the method proposed in this study for HSPMM optimisation is verified.

Abstract The prosperous development of electric vehicles has promoted the application of interior permanent magnet synchronous motors (IPMSMs). The flux‐intensifying IPMSM has attracted more attention due to its high power‐density and better flux‐weakening performance. However, the optimisation efficiency and motor performance require further study in the actual optimisation design. To this end, this study is to optimise the electromagnetic field structure of motor rotors with the back propagation neural networks (BPNN) and multi‐objective optimisation methods. Concretely, dimensional parameters of an initial motor are extracted as optimisation variables. Then, the BPNN are utilised to stimulate the motor performance obtained with finite element methods (FEM). With the trained BPNN, FEM tools are replaced in the subsequent optimisation process, which alleviates the computational burden. Besides, to address the problem of multi‐objective optimisation with inequality constraints, the sequential unconstrained minimisation technique is incorporated into the non‐dominated sorting genetic algorithm to obtain the Pareto frontier. Finally, the optimal design point is selected from the Pareto frontier. The simulation and experiment have been implemented to verify the superiority of the optimised rotor structure. Generally, this study has laid the foundation of the following motor optimisation with the higher executability and lower computational burden.

Abstract In this work, a novel dual‐stator hybrid excited linear flux switching machine (DSHELFSM) is proposed. The proposed machine is suitable for long‐stroke applications as all the excitation sources are mounted on a short mover and the stator is completely passive. Second, the proposed machine uses ferrite magnets rather than the expensive rare earth permanent magnets (PMs) with the addition of field excitation to achieve flux‐regulation capability at various field currents. An iron bridge that provides an additional path for flux linkage to complete its circuit is used. Various design parameters such as split ratio, stator pole width, width and height of PM, the width of the iron bridge, width of mover's tooth, and stator slot depth are optimised using multivariable geometric optimisation (MGO) while keeping the slot area, electric and magnetic loading constant. The optimised design has improved the performance as compared to the initial design. Furthermore, the results obtained by 2D analysis are verified by 3D analysis. Thermal analysis is carried out to set the operating limit of the proposed machine.

Abstract Operation of Vernier machines is based on flux modulation. They have some advantages including maintaining the rated torque in motor applications and the rated output power in generator applications at low speeds, high torque density and relatively low torque ripple due to their magnetic gear property and fault‐tolerance. In recent years, the motor with various topologies has been developed for different applications. Therefore, analysing and monitoring different faults is essential in the design and implementation stages. This study has two main purposes. First, to introduce an accurate frequency index independent of load variations for detecting the turn‐to‐turn short circuit (TTSC) faults in the stator windings of a permanent magnet Vernier machine. Second, modelling the machine in a healthy condition and in the presence of TTSC faults to investigate its effect on machine performance and output characteristics. An analytical model is presented using the modified winding function theory under the TTSC fault by taking into account the effect of stator slots which enhances the accuracy of the air‐gap permeance function estimation. In the process of calculating the fault index, frequency components of the output characteristics of the machine are obtained from the mathematical equations of the magnetic field. It is shown that the proposed indicators are robust against load variations.

Modular multilevel converters (MMCs) can be a reliable solution since they have modular structure and high quality output waveform for permanent magnet synchronous generator (PMSG) based wind energy conversion system (WECS). Capacitor voltage balancing in nearest level modulation (NLM) is required to keep the capacitor voltage of each submodule of MMC constant. In this paper, an efficient capacitor voltage balancing scheme under NLM is proposed for PMSG based WECS with MMC topology. Through proposed control scheme, arm voltages are separately controlled and voltage ripple of around 1.5% is obtained. This result provides high quality output waveform at the point of common coupling (PCC). Furthermore, DC-link voltage control is achieved via hysteresis current control based proportional-integral controller. The ripple of DC-link voltage is obtained quite well as nearly 0.25%. In addition, load voltage control is accomplished using dq reference frame-based voltage control scheme for voltage and frequency stabilization at the PCC by regulating the voltage at its reference value. Simulation studies show that all proposed control schemes give satisfactory results for MMC based WECS under variable dynamic operation modes. Finally, experimental verification is performed using laboratory prototype to show the applicability of the proposed capacitor voltage balancing scheme.

This article presents a real-time realization of a continuous-control-set model predictive current controller for the two types of permanent magnet synchronous machines: 1) surface-mounted permanent magnet synchronous machine (SMPMSM) and 2) interior permanent magnet synchronous machine (IPMSM). The constrained optimization problem is solved online using a slack formulation of the primal-dual interior-point method. The proposed controller is tested on a 14.5 kW SMPMSM based on the linear time-invariant (LTI) model of the machine and on a 0.5 kW IPMSM. For the latter, we present in detail how the nonlinear first-principles modeling yields the fastest possible transient as well as an offset-free steady-state performance. The experimental results were obtained at sampling times typically used in the electrical drive applications (125 and 100 $\mu$ s for the two machines, respectively). [ABSTRACT FROM AUTHOR]

This article reviews the state-of-the-art back electromotive force (EMF) based sensorless schemes for synchronous machines. Field-oriented control (FOC) of a synchronous machine requires real-time rotor position for decoupled torque and flux control. Extraction of rotor position without a sensor or sensorless control has been an enabling technology for the past few decades. Sensorless control using back EMF voltage induced by rotor movement is the most widely used method. However, the connections and differences between different methods have not been thoroughly investigated and documented. This article first reviews basic sensorless methods. The two implementation forms of an observer are examined to facilitate analysis. A detailed analysis puts in evidence the connections behind different methods in both stationary and synchronous reference frames. A summary is drawn that is meant to offer a few key points regarding different sensorless methods. Finally, a conclusion is given to summarize the major contributions of this article. [ABSTRACT FROM AUTHOR]

In high performance electric machines, the increase of fundamental frequency leads to additional losses in the winding due to parasitic effects such as the associated skin and proximity effects. In the first part, this paper presents an investigation into accurate modelling of AC losses in the winding using numerical methods and their experimental verification. Then, using experimental motorette setups, this research provides a comparative study between fixed strand positioning and fixed conductor shapes on the AC losses in the winding. It is shown that the exact position of strands in the conductor is not a critical factor; however, it is very important to control the conductor shape inside the slot. In the final section of this paper, an investigation into the relationship between AC losses in the winding and copper filling factor is presented. It is shown experimentally that counter-intuitive design choices such as using a lower copper fill factor and thicker strand diameters may be beneficial in achieving the highest overall efficiency. [ABSTRACT FROM AUTHOR]

Subdomain modeling is among the most reliable and accurate analytical tools for designing and analyzing permanent magnet machines. However, the application of the two-dimensional (2-D) subdomain model is mainly limited to permanent magnet machines with homogeneous rotor structures (with uniform permeability), such as surface-mounted or surface-inset permanent magnet machines. Solving Maxwell's equations and applying 2-D boundary conditions on structures with permanent magnets embedded in the rotor core, such as interior permanent magnet machines, are quite complex. Given the importance of enabling the tangential field component to capture accurate results, a 2-D hybrid analytical solution is proposed and applied to a multilayer interior permanent magnet machine. For this purpose, the radial components of the permanent magnet flux and the armature flux are first calculated using the magnetic circuit and the magnetic islands methods, respectively. Next, their respective tangential flux components are computed by solving Poisson's equation and applying a 1-D boundary condition along the tangential direction. Meanwhile, the stator slotting effect is included via the theory of virtual surface current. Finally, the steady-state performance metrics of the motor are calculated and verified via finite-element and experimental measurement. [ABSTRACT FROM AUTHOR]

Production deviations have a remarkable effect on the radiated sound of electrical machines, introducing additional signal components besides the fundamental field waves which significantly change and enrich the subjectively perceived sound characteristic. In literature these harmonics are mainly traced back to dynamic eccentricity, which modulates the fundamental fieldwaves. In this paper a thorough mechanic and electromagnetic analysis of a modern, well-constructed traction drive (permanent magnet synchronous machine) is performed to showthat for this typical rotor configuration dynamic eccentricity is negligible. Instead, deviations in the rotor magnetization are shown to be the dominant cause for vibration harmonics.

This paper presents an analytical study of the air-gap magnetic field of a Surface Permanent Magnet (SPM) linear machine under no load. By means of the method of images, the complex expression of the magnetic field of a conductor, inside the air gap between two smooth iron surfaces, is retrieved. Then, integrating the conductor expression, the formulation of the magnetic field of a current sheet and thus the one of a SPM, using two vertical current sheets, is obtained. At last, the no-load magnetic field expression, for a generic time instant, of a slotless machine is retrieved. The novelty of the proposed approach is the availability, due to a different calculation approach, of a unique closed-form formulation for the slotless machine air-gap field, a quantity that, in literature, is usually present in Fourier series formulation. Additionally, as a means to calculate integral quantities and show the goodness of the method a complex slotting function is introduced to account for the slotted geometry. Finally, starting from Lorenz’s force formulation, the expression of the Maxwell tensor in complex form is retrieved and the contribution of forces, integral of the complex stress tensor quantity, will be calculated and compared with FEM simulations, showing a good agreement also with the analytical slotted model.