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Featured Application: The work specifically targets the enhancement of cooling mechanisms in high-power permanent magnet electrical machines, with a direct application in improving the thermal management of stator windings in such devices. This advancement can significantly benefit sectors like aerospace, where the efficiency, reliability, and longevity of electrical machines are critical. This paper investigates innovative methods for enhancing heat transfer efficiency in high-power permanent magnet electrical machines. The objectives are to quantify the effects of increasing the air speed, increasing the turbulence intensity, and introducing the spacing between windings on cooling performance. The cooling of stator windings is studied through experimental wind tunnel testing and Computational Fluid Dynamics (CFD) modelling. The CFD model is validated against wind tunnel measurements to within 4 Kelvin (K). The results demonstrate that each enhancement method significantly improves the cooling capability. Increasing the air speed from 10 m/s to 40 m/s reduces the winding hotspot temperature by 34%. Introducing a high turbulence intensity of 40% leads to a 21% lower hotspot temperature compared to 0.5% turbulence intensity. Creating a 1.5 mm spacing between coils also substantially improves convection and conduction heat transfer. Overall, combining these optimised design parameters yields over a 40% reduction in hotspot temperature compared to the original design. This research provides practical guidance for maximising heat transfer efficiency in high-power permanent magnet machines, without increasing complexity. The findings will lead to higher machine efficiency, reliability, and longevity for aerospace and other applications. [ABSTRACT FROM AUTHOR]

For the short-term high torque output, an improved model predictive direct torque control (MPDTC) method with field enhancing is proposed to increase torque. In order to avoid the possible loss of synchronism while increasing torque, the MPDTC method limits the load angle in the cost function. Under the constant load angle limitation, the improved method increases the torque output capability by increasing the magnetic field. This paper starts from the torque calculation, theoretically analyzes the torque-load angle characteristics, and illustrates the flux vector trajectory with the voltage limit circle and current limit circle. The proposed method maintains the dynamic and static performance of the traditional MPDTC method while ensuring the system stability. The experimental results show that the torque capacity of the proposed method has been improved, and it has stable extreme output torque. So, some applications, such as electric load simulators, can choose the motor with small capacity and small inertia, thereby weakening negative effects of the inertia torque. [ABSTRACT FROM AUTHOR]

This paper proposes a novel algorithm which made it feasible to predict the harmonic fault signatures under dynamic eccentricity in Permanent-Magnet synchronous machines with concentrated non-overlapping winding for any slot-pole combination. In the literature, only the appearance of the fractional harmonic components related with the pole number has been proposed but there are no studies to predict which exact components will rise in each topology. Initially, a mathematical equation is derived for the machine EMF under dynamic eccentricity based on the air gap permeance model. Later on, the terms of this equation are inserted in a Fault Signature Block Binary Array in which the position of each cell expresses a specific harmonic frequency component. After substitution of the machines parameters, the array results with zero and nonzero terms. The positions of the nonzero terms express the frequency components excited by this particular fault. 3-D FEA and experimental results of a Permanent-Magnet Axial-Flux Machine are used to validate the proposed algorithm. [ABSTRACT FROM AUTHOR]

Partial demagnetization is a condition that may occur in Permanent Magnet machines due to overloading or thermal stress. Whenthis happens, the magnetic field locally weakens leading to an asymmetry of the air-gap field. This asymmetry will cause harmonics, which will be expressed as extra losses and mechanical oscillations. Moreover, since the field becomes weaker, more current is required to serve the load leading to less efficiency, increased losses and consequently increase of the temperature, which will cause further progression of the demagnetization severity until a total machine breakdown. Several methods have been proposed in the literature for the online detection of the demagnetization, however they have not related the fault to the manufacturing characteristics of the machine, which play an important role on the expected harmonic index and the associated fault signatures. This paper presents for the first time a detailed analytical investigation of the expected harmonics in the stator current spectrum in case of demagnetization, as a function of the stator winding and number of poles. The analytical results are verified by extensive simulations via the finite element method and experimental testing. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of stator/rotor pole number combinations and permanent magnet (PM) numbers on electromagnetic performance of consequent-pole hybrid excited flux reversal machines (CP-HEFRMs), which have different numbers of PM poles and iron poles and concentrated AC and DC windings on the stator and a salient pole rotor. PMs in the slots of one stator pole are magnetized radially in the same direction, while opposite on adjacent stator poles. Magnetic field paths of DC, PM, and hybrid excitations are investigated. The phenomenon of flux cancellation, i.e., PM and DC MMFs in CP-HEFRMs are of opposite polarities in the flux-enhancing operating mode, is revealed and verified, for the first time, as the key feature that makes CP-HEFRMs different from other hybrid excited machines. Consequently, the saturation in stator pole and yoke can be mitigated and hence the overload capability of DC excitation is enhanced, which is verified by finite element analysis (FEA). Global optimizations are utilized to obtain the optimal rotor and stator pole number combinations and PM numbers for each stator pole. Torque, torque ripple, inductance, unbalanced magnetic force, and flux regulation capability are compared for different PM numbers and rotor pole numbers. Comparisons are made on consequent-pole and non-consequent-pole topologies in terms of torque capacity, flux regulation capability, and PM consumption to further illustrate the advantages of consequent-pole topology. A prototype machine is built and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

Consequent-pole (CP) permanent magnet (PM) configuration suffers asymmetric electromagnetic characteristics although it saves PM usage. The CP-based stator-PM synchronous machines are investigated in this paper, with particular reference to symmetrical issues. The electromagnetic performances of the CP-based stator-PM synchronous machines are firstly evaluated. Afterwards, the rule of even order harmonics cancellation is presented for different slot/pole number combinations and winding layouts, based on which symmetrical phase flux-linkages can be obtained although the unbalanced magnetic flux naturally occurs. Moreover, based on the three-dimensional finite element analysis, the unipolar end leakage-flux caused by the asymmetric magnetic field is identified, and the risk of the shaft magnetization is revealed. Finally, a pair of prototype machines are fabricated and measured to validate the analyses. [ABSTRACT FROM AUTHOR]

Asymmetric interior permanent magnet (AIPM) rotor topologies can achieve torque enhancement in IPM synchronous machines without the increase of PM usage due to utilizing magnetic-field-shifting (MFS) effect by reducing the current angle difference between maximum PM and reluctance torque components. This paper investigates the influence of armature reaction on MFS effect in AIPM machines. A general model of IPM machines considering MFS effect is analytically developed and the AIPM and IPM machines using the same stator, rotor diameter and total PM amount are comparatively studied. It shows that the armature reaction affects the MFS effect in both AIPM and IPM machines and the influence is more significant in AIPM machine. The relationships between MFS effects in PM flux-linkage and inductance characteristics and current angles for maximum PM and reluctance torque components are revealed. It confirms that the change of current angles of torque components is due to the MFS effect in PM flux-linkage and inductance characteristics in both AIPM and IPM machines. Besides, the developed machine model considering MFS effect is verified by finite element analysis. Finally, a small-scale AIPM machine prototype is fabricated and measured to validate the finite element analysis. [ABSTRACT FROM AUTHOR]

A comparative study of new partitioned stator hybrid excitation axial flux switching permanent magnet (HEAFSPM) motors with different partitioned excitation stator topologies for in-wheel traction applications is presented in this paper. The realization approaches of the partitioned stator HEAFSPM motor are discussed, and the motor topology with windings and permanent magnets (PMs) separately setting on different stators is selected in view of the advantageous structure for thermal management. On this basis, two partitioned excitation stator topologies including C-type tooth core and T-type tooth core stator configuration are proposed, and the air-gap flux modulation and flux regulation principle of the motors are analyzed. In addition, the design method of the partitioned stator HEAFSPM motor considering the effect of hybrid excitation sources is provided, and the two motors with different tooth cores are designed respectively. Meanwhile, for a fair comparison, the multiple objectives optimization method coupled with the sensitivity analysis is employed to optimize the two motors. The electromagnetic performances, anti-demagnetization capability, and flux regulation performance of the two motors are all investigated in detail. Finally, two prototype motors are fabricated and tested. Both the theoretical analysis and experimental results verify the effectiveness and reasonability of the motor. [ABSTRACT FROM AUTHOR]

In this paper, a high-speed permanent magnet (HSPM) motor having 6-slot/2-pole (6s/2p) number combination and 2 coil-pitch windings are developed for domestic appliance application. Two HSPM motors with different layouts of 2 coil-pitch windings are optimized and their electromagnetic performances are evaluated. The best winding configuration is then identified for shorter motor axial length and larger torque density. Since 3-slot/2-pole (3s/2p) HSPM motors with non-overlapping windings have the same winding factor, a comparison between 3-slot and 6-slot motors is also conducted, particularly for torque density, losses, and unbalanced magnetic force (UMF). It shows that 6s/2p PM motors with 2 coil-pitch windings are suitable for high-speed application without UMF and less rotor PM loss. Finite element predicted electromagnetic performances are validated by experiments made on two prototype motors. [ABSTRACT FROM AUTHOR]

Linear permanent magnet Vernier machines (LPMVMs) is an attractive solution for stroke and direct-drive applications. Several LPMVM topologies have been presented for different applications that operate based on magnetic flux modulation. LPMVMs have some advantages including high force, and torque density at low speeds. This paper introduces a double-excited linear Vernier machine for wave energy conversion. To model the machine, finite element analysis and nonlinear equivalent network model are used. To improve the accuracy of the model and compact the network, a new meshing method is proposed. For better continuity in the output waveforms of the machine, special positioning is utilized. The end-effect is modeled using two separate networks. Finally, the modeling and simulation results are compared with each other and validated experimentally. [ABSTRACT FROM AUTHOR]

The flux-switching permanent magnet (FSPM) machine has aroused wide interest recently due to high-power density, favorable PM cooling capability, and essentially sinusoidal electromotive-force (EMF) waveform per phase. Previously, the phase back-EMF generation mechanism of FSPM machines is exposed from a flux-switching perspective, however, which is rethought from the viewpoint of air-gap modulation magnetic field in Part I as in this article, and electromagnetic torque generation mechanism of FSPM machines will be reported in Part II as another sister paper. With the aid of magnetic field modulation theory, the air-gap PM magnetic field and back-EMF of the FSPM machine are modeled based on modulation and winding functions. Their characteristics are analyzed in detail and consequently, principles concerning FSPM machines on arbitrary stator-slot/ rotor-pole combinations can be obtained, including the basic feature of FSPM machines, the principle and necessary conditions for the back-EMF generation, the fundamental reason of sinusoidal back-EMF waveform, and the contributions of modulation harmonics to phase back-EMF. Finally, experimental verification on a 12s/10p prototyped machine is conducted. [ABSTRACT FROM AUTHOR]

The design rules of winding configurations and stator-pole/rotor-tooth (SP/RT) number combinations of doubly-fed flux-switching permanent magnet (DF-FSPM) machines are investigated in this paper based on coil electromotive force (EMF) vectors. The relationships between the components of stator and rotor coil-EMF vector diagrams are unveiled at first, including the numbers of stator and rotor phases, and the numbers of stator and rotor spokes. Then, the SP/RT number combinations are derived considering feasible stator/rotor phase number combinations and different winding configurations. The SP/RT number combinations are optimized considering the winding factors, magnetic field harmonics, unbalanced magnetic forces and machine diameter. It is shown that both of the stator and rotor pitch factors increase when the SP and RT numbers get closer. Furthermore, the influence of winding configurations and SP/RT number combinations on electromagnetic performances of DF-FSPM machines are analyzed by finite-element method. Finally, the analysis results are validated by experiment. [ABSTRACT FROM AUTHOR]

This paper formulates the difference in base frequency and maximum torque between distributed and concentrated windings taking into account the air-gap modulation of concentrated-winding permanent magnet (PM) motors. The design superiority is typically confirmed for each winding type during a development period by using time-consuming finite element analysis (FEA). We propose a quantification that enables motor designers to easily judge, at the initial design stage, a superior winding type and to shorten a design period. Throughout our formulation, we found that the distributed-winding PM motors, in principle, have larger q-axis inductance and smaller d-axis inductance than the concentrated-winding motors, which leads to a decrease in the base frequency. On the other hand, the distributed winding inherently has higher winding factor and needs shorter stack length of core than the concentrated winding for identical torque output, which results in an increase in the base frequency. And also, we theoretically quantified the difference in reluctance-torque contribution between the two winding types and found that it was too small to have much impact on practical design. We applied the proposed formulae to a 0.2-kW concentrated-winding Nd-Fe-B magnet motor and were able to quantify the base frequency, the maximum torque, and the minimum stack length of core for a distributed-winding motor with high accuracy without having to rely on FEA. The FEA and measurement results demonstrated the validity of the proposed approach for the fabricated distributed-winding PM motor. [ABSTRACT FROM AUTHOR]

It has been proved that dual-armature permanent magnet (PM) machines have higher power density than conventional PM machines under the same copper loss. However, the thermal conditions of these machines are different. This paper makes a fair comparison between a dual-armature linear switched flux PM machine (DALSFPMM) and a linear surface-mounted PM machine (LSPMM) by considering both electromagnetic performances and thermal conditions. First, the topologies of two machines and platform are introduced. Then, the 2D and 3D finite element (FE) models are employed for the electromagnetic and thermal analyses, respectively. During the machine optimization, the thermal analysis is used to determine the copper loss under the fixed machine dimensions, while the electromagnetic analysis is used to optimize the machine dimensions under the fixed copper loss. After iterations, two machines are optimized and their performances are compared. Under the limitations of 80 °C maximum PM temperature and 120 °C maximum winding temperature, the DALSFPMM can exhibit 38% higher thrust force density for the continuous duty and up to 43% higher thrust force density for the short-time duty. Finally, a prototype machine of DALSFPMM is tested to validate the analyses. [ABSTRACT FROM AUTHOR]

The brushless doubly-fed machine (BDFM) has two stator windings with different pole numbers, supplied with different frequencies. Therefore, the distribution of magnetic fields in stator and rotor iron is complex. In addition, the stator flux density distribution is non-sinusoidal and has a DC offset at the natural speed. This makes the use of conventional hysteresis models utilised for sinusoidal fields impractical for the BDFM. In this paper a new hysteresis model is proposed for the BDFM stator iron based on the scalar Preisach model. The rotational characteristics of the magnetic fields in the BDFM are also considered and their effects in generating iron losses are assessed. 2-D time-stepping finite element (FE) models are developed for a prototype D160 BDFM to estimate iron losses and are validated by experiments. [ABSTRACT FROM AUTHOR]

In this paper, a novel dual-armature (DA) flux reversal permanent magnet (PM) machine with halbach array magnets in the stator slot opening is proposed, which is abbreviated as DA-Halbach machine. Besides the stator armature windings, another set of windings is added in the rotor slots to further enhance torque performance via fully utilizing the rotor space. The influences of major geometric parameters on torque performance are investigated. Both DA-Halbach machine and conventional Halbach machine are optimized with the goal of maximum torque under the same copper loss using finite element (FE) method. The electromagnetic performance of two optimized machines are compared, the results show that the proposed DA-Halbach has larger torque and smaller torque ripple than conventional Halbach machine. When compared with surface-mounted PM machines, the proposed DA-Halbach machine still show better torque performance. [ABSTRACT FROM AUTHOR]

Aiming at the problem of high winding temperature caused by the large armature winding current of permanent magnet synchronous motor (PMSM) for compressors, a 560 kW PMSM for a compressor was studied. The three dimensional global fluid-heat coupled heat transfer model is established and is discretized by the polyhedral mesh. The fluid and thermal coupling field of a permanent magnet motor are numerically calculated when the rotor rotation is considered. The temperature distribution characteristics of the end windings at different positions are analyzed. Further, the structure of the motor cooling system is improved. The effects of different ventilation modes on the temperature distribution of the motor are compared and analyzed. The temperature distribution of the stator windings under different armature currents is calculated. The calculation results of the end winding temperature are compared with the measured data, verifying the correctness of the calculation method. Conclusions have been obtained that are helpful to the design and operation of the compressor water-cooled permanent magnet synchronous motor. [ABSTRACT FROM AUTHOR]

Permanent magnet machines are widely applied in motor drive systems. Therefore, condition monitoring of permanent magnet machines has great significance to assist maintenance. High temperatures are accountable for lots of typical malfunctions and faults, such as demagnetization of the permanent magnet (PM) and inter-turn short circuit of stator windings. Therefore, temperature monitoring of the PM and stator windings is essential for reliable operation. In this paper, an overview introducing and evaluating existing thermal monitoring methods is presented. First, the mechanism of thermal-caused failures for the PM and stator windings is introduced. Then, the design procedure and principles of existing temperature monitoring methods are introduced and summarized. Next, the evaluations and recommendations of application feasibility are demonstrated. Finally, the potential future challenges and opportunities for temperature monitoring of the PM and stator windings are discussed. [ABSTRACT FROM AUTHOR]

The interior permanent-magnet synchronous motor (IPMSM) has been widely used as the traction motor in electric/hybrid vehicles because of its high torque density and wide operating speed range. During the operation of the IPMSM, the stator winding temperature and magnet temperature should be monitored to prevent winding insulation breakdown and irreversible demagnetization and to improve the torque accuracy. This article devised a method involving the use of a high-frequency (HF) resistance and an HF inductance for estimating these two temperatures at low motor speeds. The relationship between the HF impedance and both temperatures was determined and verified using an experimental setup in which both temperatures could be measured. Based on the relation, the temperature estimation method has been proposed, in this article, and verified by the experimental test. The proposed method was used to estimate the stator winding and the magnet temperatures simultaneously for 6000 s, and the maximum error was 6 °C and 3 °C for the stator winding and magnet temperature, respectively, even when the load and the temperatures varied considerably. [ABSTRACT FROM AUTHOR]

This article proposes a series of split-tooth stator permanent magnet (PM) Vernier machines with zero-sequence current excitation, which integrates enhanced torque density and flux adjustment capability. The key is to design the split tooth to exert desired dual magnetic field modulation effect so as to efficiently utilize the hybrid magnetic fields by the PM and zero-sequence current. Meanwhile, with the split-tooth design, the paralleled flux paths are achieved to offer improved flux regulation capability and reduced PM demagnetization risk. In this article, the machine topologies and operation principle are introduced. Hybrid excitation magnetic field is analyzed with the consideration of dual magnetic field modulation of split-tooth structure. Influences of split tooth and PM on torque and flux regulation capability are analyzed. Electromagnetic performances of the proposed machine are analyzed and compared. A prototype is manufactured and tested to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

Axial-flux permanent magnet (AFPM) machines are gaining popularity in low-speed and high torque applications due to their high torque density, high efficiency, and compact structure. In this article, a dual-rotor slotless AFPM (DRSAFPM) machine equipped with equidirectional toroidal winding (EDTW) is proposed and compared with that equipped with conventional single-layer and double-layer concentrated windings (CWs). First, the differences between the DRSAFPM machine with EDTW and that with conventional CWs in coil layout, electromotive force (EMF), and winding magnetomotive force are revealed. Considering the special coil layout of the EDTW, the coil factor and size equations of the DRSAFPM machines with EDTW and conventional CWs are presented. Second, the electromagnetic performance including air-gap field, back-EMF, torque, and efficiency of the DRSAFPM machines with EDTW and conventional CWs are analyzed based on the three-dimensional finite-element method. The simulation results validate the correctness of the coil factor and size equations and indicate the EDTW–DRSAFPM machine has superiority in back-EMF amplitude and torque density. Finally, a prototype of the EDTW–DRSAFPM machine is manufactured and tested, which validates the feasibility of the EDTW–DRSAFPM machine and the correctness of the analysis. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous motors (PMSMs) due to their numerous advantages, such as simple and compact design, easy production and high power-to-weight ratio, high power factor in the range of constant torque, low inertia, and more precise control compared to other electric motors, are increasingly used in various applications, such as electric vehicles, wind power, home, and industrial appliances. However, PMSMs, such as other electrical machines, may subject to various types of damage during the operation. Due to their use in devices of a critical nature (e.g., transport applications), the detection of these damages at their initial stage constitutes an extremely important issue. In this article, we investigate the possibility of the permanent magnets (PMs) faults detection of PMSM using a convolutional neural network (CNN) based on the raw stator current data. The article aims to show the possibility of detecting the PM demagnetization using the information obtained directly from the measured current signal as well as indicate the influence of simultaneous incipient interturn short circuits and the operating condition of the drive on the accuracy of the developed diagnostic system. The results of the experimental research carried out on a specially designed PMSM show the impressive capability of the developed CNN-based diagnostic system to precisely detect the initial phase of PMs damage. [ABSTRACT FROM AUTHOR]

In this article, an iron loss for the flux switching permanent magnet machine with the pulsewidth modulation (PWM) inverter supply is calculated based on the general airgap field modulation theory (GAFMT). First, the amplitudes and rotation speeds of the main space harmonics of the airgap magnetic flux density with the supply of PWM harmonics are calculated based on the GAFMT. When calculating the source magnetizing magnetomotive force based on the GAFMT, the equivalent magnetic circuit is applied to calculate the working point of the permanent magnet. Second, each spatial harmonic in the airgap magnetic field is synthesized by an equivalent current layer in the airgap and then is substituted into the 2-D finite element analysis models to calculate the iron losses. Finally, the iron losses calculated by the proposed method with different speeds, loads, and control strategies are compared with the experimental results. [ABSTRACT FROM AUTHOR]

Dual permanent magnet (PM) machines have attracted numerous interests due to the high torque density and compact volume. This article investigates a synergistic PM machines with the synergies of flux switching and flux reversal effects. The flux-reversal and flux-switching PM (FSPM) flux paths circulate from two sides of the split teeth separately, which avoid the over-saturation with dual PM excitations. The preferred stator and rotor pole number is derived from a simplified analytical model and the influence of leading parameters is analyzed as design guidelines. Furthermore, the synergistic stator PM machine is optimized and compared with FSPM machines. It is revealed that the synergistic stator PM machine exhibits ∼20%, ∼10%, and ∼17% higher torque density than conventional FSPM machine, C-core FSPM machine, and E-core FSPM machine, respectively. Besides, good flux weakening capability is achieved with a larger inductance than conventional FSPM machine, and higher efficiency is obtained at both low-speed and high-speed operations. Finally, an experimental prototype is fabricated to validate the proposed concepts. [ABSTRACT FROM AUTHOR]

Thanks to the absence of rotor windings and permanent magnets, switched reluctance motors have a small weight construction. The integration of a modular power converter in a switched reluctance motor leads to a highly compact and fault-tolerant motor drive with small weight and high power density. In this article, a polygon-retrofitted integration topology is proposed for switched reluctance motors. Both the switched reluctance motor and the power converter are cooled with one shared cooling circuit. The power converter is designed and implemented using silicon carbide technology for its low losses and small thermal resistance. The proposed integration topology is extensively studied using multiphysics modeling and experimental measurements on a fully integrated rotating setup. A highly compact and power dense drive of 3.1 kW/L is obtained. [ABSTRACT FROM AUTHOR]

Variable reluctance resolvers (VRRs) have been widely used for rotor position detection in harsh working conditions. However, conventional installation of VRRs inevitably occupies the axial space of machine systems, and may weaken the reliability of rotor position detection encountering shock and vibration. In this article, a novel VRR structure with inner stator is investigated, which is radially integrated inside a permanent magnet synchronous machine (PMSM) to construct compact machine topology. The hybrid machine topology is first discussed, and detailed electromagnetic design is carried out. Improved analytical analysis on air gap flux density distribution and inductance evaluation of the integrated VRR is derived based on modified winding function approach, and testified by finite element analysis. A prototype is manufactured from an existing 2.2 kW PMSM, and experiments are conducted to validate the effectiveness of proposed machine topology. [ABSTRACT FROM AUTHOR]

Winding inductance is a crucial parameter of machines, which plays an essential role in flux-weakening capability, reluctance torque, power factor, etc. In this article, winding inductance characteristics of flux-switching permanent magnet (FSPM) machines are investigated from the perspective of air-gap modulation magnetic field. With the aid of the general air-gap field modulation theory, the air-gap magnetic field contributed by an arbitrary energized winding of FSPM machines is modeled and analyzed. Then, an analytical expression of winding inductance is derived based on winding function and single-phase magnetic field, through which the relationship between winding inductance and single-phase magnetic field harmonics is unveiled. It is found that the direct current (dc) and 2nd harmonic components of winding inductances in FSPM machines are caused by the dc and 2nd time-harmonic components of primitive harmonics, respectively, which are essentially different from that of traditional interior permanent magnet or reluctance machines. Finally, experiments on a prototype three-phase 12/10 FSPM machine are conducted to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

Dual-three-phase permanent magnet synchronous machines (DTP-PMSMs) are famous for their fault-tolerant capability. However, the complex modeling, high copper loss, and torque ripple under postfault operation limit their further application. In this article, a fault-tolerant control (FTC) strategy is developed for DTP-PMSMs under the open-phase fault (OPF) with straightforward modeling and smooth output torque. The virtual healthy DTP-PMSM model, where the coordinate transformation, the modulation strategy, and the controller structure remain unchanged under OPF, is adopted in the proposed FTC scheme. And the current references are derived in sinusoidal waves with minimum copper loss. The inaccurate transmission of control signals under OPF is also focused on. Comprehensive theoretical analysis shows the relationship between the controller output voltage and the actual stator voltage should be considered in the proposed FTC strategy; otherwise, distortion in torque and current will be introduced. The voltage compensation is utilized to compensate for the voltage difference and ensure the smooth torque output. Besides, a quasi proportional resonance controller is designed to further suppress the residual torque ripple. The proposed strategy will not induce complex implementation and heavy computation burden. The simulation and experimental results prove the analysis and the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Dual-pole line start permanent magnet (PM) synchronous machine is an emerging technology for replacing induction machines in two-speed applications, such as air coolers, compressors, and pumps. The machine structure includes two magnetic pole numbers on a single rotor layout and two separate sets of stator windings. Due to the unconventional and complex rotor structure, to this date, the design and analysis have solely been based on finite element (FE) method. This article aims to analytically validate the theory and the overall functionality of dual-pole PM machines in both steady state and transient regime. For this propose, a detailed magnetic circuit model is developed for calculating the PM flux distribution and the back electromotive force waveform. However, a single magnetic circuit cannot adequately represent the flux flow of the armature reaction, since the path of the armature flux is a function of rotor position. This is even more challenging in dual-pole machines, where the armature flux is originated from two different sets of stator winding. To avoid the necessity of having multiple magnetic circuits, the concept of magnetic islands is employed to capture the motor response at the loaded condition. For verification, analytical results are all supported via FE, and partially with experimental tests. [ABSTRACT FROM AUTHOR]

In the high-speed flux-switching permanent magnet (FSPM) machine, the ac copper loss issue in the armature winding conductor is very prominent, due to the high-frequency leakage magnetic field in stator slot, which seriously affects the machine performance. To model and calculate ac copper loss more accurately, a coupled electric circuit-magnetic field model is constructed based on 2D-finite element method, and consequently the influence of modeling methods and winding types on ac copper loss calculation of a 12-slot/10-pole (12/10) 54.7 kW/10 kr/min FSPM machine is investigated. First, ten simplified ac copper loss calculation models are established to deal with the problem of large consumption of calculation time and computer resources caused by the excessive number of wires, small size of winding conductors, high precision modeling, and mesh refinement. Second, the influences of voltage-/current-source and steady/rotating rotor are considered, and the ten models are evaluated in terms of computing time and accuracy. Third, based on the preferred model from the ten models, the effects of frequency, round/flat wires, and wire sizes on ac copper loss are further studied. Fourth, to investigate the influence of flux leakage at the end of winding on ac copper loss, a 3-D ac copper loss calculation model with different axial lengths of winding end space is established. Fifth, the change process of ac copper loss and transient temperature of winding under short time overload condition are obtained combined with the bidirectional coupling model between electromagnetic and thermal field method through multiple iterations of electromagnetic loss and temperature. Finally, the stator modules of round and flat copper wires are manufactured, respectively, and an experimental modular device is built to measure the ac copper loss, which confirms the improved accuracy of the predictions by the proposed model. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Rotor angle is essential in permanent-magnet (PM) brushless machines. Recently, an embedded magnetic encoder (EME) scheme, consisted of linear Hall sensors installing inside of the PM machines, has been proposed to sense the flux density and consequently provides rotor position. Compared with traditional optical encoder and resolver, the linear Hall sensor prevails over in both space and cost. The aforementioned scheme is employed successfully in rotor-PM machines, where a PM-excited field rotates at the synchronous speed. In this article, the feasibility of EME in stator-PM flux-switching machine is validated, where PMs are located in stator, resulting in a stationary PM field. The stator slots are selected as installation position of linear Hall sensors to avoid changing the existing structure of machines. The variation of linear Hall signal is due to the changing reluctance of rotor rather than rotating PMs. Then, a decoding algorithm is designed based on an add-up operation, a complex coefficient filter, and a synchronous reference frame phase-locked loop. Finally, experiments on a prototype machine are conducted to validate the effectiveness of EME scheme under both speed-varying and load-varying conditions. [ABSTRACT FROM AUTHOR]

The aim of this study is to introduce the maximum torque per total ampere (MTPTA) control strategy for brushless doubly fed induction machine drives taking iron loss into account. In this regard, the condition for realizing the MTPTA is investigated in the presence of iron loss by a theoretical approach. It is shown the proposed strategy is realized when the MTPTA criterion tracks zero as reference signal. As a result, the current is not only shared between the stator windings fairly but also total stator currents are minimized for a given torque. The experimental results confirm the performance of the proposed control strategy. [ABSTRACT FROM AUTHOR]

The mechanism of torque ripple generation by time and space harmonic magnetic fields in permanent magnet synchronous motors is investigated to obtain advanced motor designs. The general expression between the torque ripples and harmonic air-gap flux densities in the motor is derived by using Maxwell stress tensor. Both the numerical and experimental verifications of this expression are carried out. By using this expression, the difference of the torque ripple generation between the surface and interior permanent magnet synchronous motors are discussed. Based on these investigations, the shape of the rotor surface of an interior permanent magnet motor is optimized. It is clarified that specific harmonic components of thetorque ripples in interior permanent magnet synchronous motors can be reduced to be nearly zero by optimizing the rotor surface shape. [ABSTRACT FROM AUTHOR]

In this article, an axial-flux permanent-magnet (PM) Vernier machine with the triple-stator, spoke-type PM rotor, and toroidal winding wound on the innerstator is proposed. Benefited from the flux focusing spoke-type PM rotor and short end length toroidal winding, the proposed machine has a high torque density and the improved power factor. Based on the air-gap permeance function, the analytical expression of the proposed machine is derived to qualitatively analyze the machine's performance. The quasi-three-dimensional (3-D) finite element analysis (FEA) is adopted to optimize the design parameters, such as innerstator diameter, PM thickness, and slot opening width. The quasi-3-D FEA results match well with the 3-D FEA. The 3-D FEA results show the torque densities of the proposed machine reach 49.4 Nm/L and 11.4 Nm/kg, respectively, under the 232 A/cm average electrical loading. The performances, such as overload capacity, PM demagnetization, and PM and core losses, are also analyzed by 3-D FEA. The comparison with the other axial-flux PM Vernier machine is conducted, and the results reveal that the proposed machine has the great advantages of the torque density and power factor. Since the prototype is not built, in this article, the assembly scheme and thermal behavior of the proposed machine are discussed. [ABSTRACT FROM AUTHOR]

This article proposes a consequent-pole unequal Halbach vernier wheel motor (CPUHVWM), which effectively reduces the self-flux leakage between permanent magnets, and an optimization method is proposed to improve the motor optimization efficiency and shorten the optimization time. The key variables are selected by the sensitivity analysis, and a polynomial function suitable for the optimization algorithm is constructed based on the response surface method. Based on the particle swarm optimization algorithm, the weights of different particle search areas are assigned to improve the overall optimization efficiency of the algorithm. Furthermore, to verify the superiority of the performance of the proposed structure and the applicability of the algorithm, the other two similar motor structures are compared, and the algorithm is adopted for the optimization. The optimized electromagnetic characteristics are compared by the finite element method. Finally, the prototype with the optimal parameters is built, and the effectiveness and advantages of the optimization algorithm are verified by experiments. [ABSTRACT FROM AUTHOR]

This article presents a novel flux-switching (FS) machine adopting star-array permanent-magnets (PMs), termed as star-FSPM machine. In comparison with the conventional spoke-FSPM machine, the proposed one can achieve not only enhanced flux-concentration effect, but also enlarged stator-slot area, thus improving PM utilization ratio and torque density. The harmonic characteristics of both PM field and armature reaction field in the star-FSPM machine are investigated based on the field modulation theory. More importantly, the torque generation mechanism of the star-FSPM machine is also investigated and compared with that of the spoke-FSPM machine. The results show that the proposed machine can utilize the working harmonics more effectively for torque generation. Afterwards, the electromagnetic performance comparison of four PM machines is carried out by finite-element analysis. It is found that the proposed star-FSPM machine exhibits improved PM utilization ratio and enhanced torque density as compared to the spoke-FSPM machine. Finally, the theoretical analysis and FEA results are verified by experimental measurement. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous motors (PMSMs) with nonconcentric magnetic poles (NCMP) structure are widely used as high-precision servo motors. The current subdomain method mainly equates the NCMP to a rectangular magnet to make each subdomain boundaries of magnet parallel when calculating the magnet eddy current loss (ECL), which results in a lower accuracy of the calculation. This article divides the NCMP into nonconcentric region and concentric region along the radial direction. The nonconcentric region is further divided along the circumferential direction, and each divided region has a single thickness. Based on the subdomain method, a novel analytical method of magnet ECL in PMSMs with NCMPs is proposed. Moreover, the three-dimensional distribution coefficient of ECL in the NCMP is derived by the equivalent impedance method. The effects of eddy current reaction and stator slotting are taken into account to improve the calculation accuracy. Then, through theoretical derivation, the relationship between the minimum magnet loss and the pole parameters is obtained, which provides a reference for the design of NCMPs. Finally, the loss separation experiment is performed on four prototypes with NCMPs. The experimental results, finite element method results and analytical results are compared to verify the correctness of the model. [ABSTRACT FROM AUTHOR]

This article presents a new type of surface-mounted three-phase permanent magnet synchronous motor with the same number of poles and slots which has obvious advantages in cogging torque. Since the same-pole and same-slot three-phase permanent magnet motor has three or more slot types and the slots are not evenly distributed on the circumference, this article adopts an accurate subdomain model that considers the position and slot width of each slot separately to perform an analytical calculation of the magnetic field. The motor is divided into three subdomains and modeled by Maxwell’s equations, and the magnetic scalar vector equation satisfied by each subdomain is solved by the method of separation of variables. A 24-pole 24-slot three-phase permanent magnet motor consisting of 13-pole 12-slot and 11-pole 12-slot is used to verify the correctness of the proposed analytical computational model. Compared with the finite element analysis, the proposed analytical model shows high accuracy in the calculations of the magnetic flux density of the three subdomains. [ABSTRACT FROM AUTHOR]

This article presents an analytical method to predict the magnetic field of eccentric surface-mounted permanent magnet synchronous machine (SPMSM) by applying the hybrid magnetic circuit and subdomain method. Taking stator saturation into account, the surface current is appended to the stator coil conductor, which can generate a magnetomotive force (MMF) to compensate the MMF drop across the stator core. The rotor yoke saturation effect is modeled by increasing the air-gap length. To solve the problem resulted from rotor eccentricity in analytical analysis, an equivalent transformation method is given. The transformation principle is that the eccentric machine can be equivalent to a concentric one with redistributed PM remanence and armature current density. On this basis, the subdomain method is adopted to predict the magnetic field of the reestablished machine. The proposed analytical method is implemented and evaluated on the 6p/36s and 8p/12s SPMSM and exhibits good agreement with the FEM and experiment results. [ABSTRACT FROM AUTHOR]

A generalized fault-tolerant control (FTC) strategy for the field-oriented control (FOC) and direct torque control (DTC) of five-phase fault-tolerant permanent magnet (FPFTPM) motors under various open-circuit faults is presented in this article. Most previous studies regarding FTC target a specific primary control algorithm and involve different reduced-order transformation matrices and additional current controllers, which increase the complexity of the entire drive system. In this study, a solution to the aforementioned problems is devised by developing optimal fault-tolerant voltages, which are derived from fault-tolerant mechanism analysis and steady-healthy design. Because the coordinate transformation need not be changed and additional voltage compensation is not required, a minimal control drive system reconfiguration under various open-circuit faults can be achieved to avoid accommodating the change of the primary control algorithm. The proposed control strategy not only improves the torque performance and dynamic response under healthy and fault conditions, but also adapts to both FOC and DTC. Experimental results for a 2 kW FPFTPM motor prototype are provided to evaluate the proposed strategy. [ABSTRACT FROM AUTHOR]

With the introduction of stricter energy-efficiency-ratio regulations, the surface-mounted permanent-magnet motor (SPM) is gaining increasing attention due to its inherent high-power density. This article investigates the feasible SPM structures for refrigerant compressor applications, particularly those used in metal industry factories with high surrounding temperatures so that cost-effective solutions can be achieved. A theoretical model is first established to aid structural parameter optimizations and the management of specific operational objectives and constraints; multiple SPM arrangements are investigates, with ease of manufacturing implementation being one consideration, as shown in Liu et al., 2021. Detailed finite element calculations and experimental measurements are performed to develop feasible SPMs with optimized structural arrangements that meet the desired operational objectives. [ABSTRACT FROM AUTHOR]

In this article, the permanent magnet (PM) loss in spoke-type permanent magnet vernier motors (ST-PMVM) with different stator topologies is investigated and compared for in-wheel direct drive. First, four ST-PMVM with split-pole and open-slot stators are designed for the in-wheel limited requirements. Besides, based on the PM loss model, the dominant influences of both slot and subharmonics on PM loss are highlighted. Then, the quantitative contributions of the air-gap magnetic field harmonics on torque and PM loss are investigated, which embodies the inherent characteristic of larger PM loss in PMVM. Furthermore, the stator tooth parameters, the slot opening width, and auxiliary slot depth on torque and PM loss are described, and then a parameter titled as the slot opening ratio is introduced to evaluate the relationship of various slot opening width combinations. It shows that there exists an irreconcilable contradiction between the torque and PM loss in PMVM, especially in split-pole types. Finally, a prototype was manufactured, and the theoretical results and finite-element analysis results match well with the experimental results. [ABSTRACT FROM AUTHOR]

A simplified universal fault-tolerant direct torque control (FTDTC) strategy of five-phase fault-tolerant permanent magnet (FPFTPM) motors under various open-circuit faults is presented in this article. In the proposed FTDTC strategy, the fault-tolerant currents are derived from the fault-tolerant mechanism analysis and steady-healthy design. The problems of existing FTDTC strategies that need to change coordinate transformation and add extra voltage compensation can be overcome. Thus, the minimal control drive system reconfiguration under different faults can be realized in the real sense. Especially, the steady-healthy controller is designed to suppress the torque ripples and achieve the high-quality torque given even under fault operation conditions; then, it is not necessary to set a special voltage vector or add a PI controller. Furthermore, the FTDTC strategy is improved to be realized under the dq coordinate system based on the flux adaption. Hence, the reduced d-axis current under different operating conditions, including fault conditions, can be ensured. This FTDTC strategy without any control reconfiguration is proposed under the premise of ensuring good performance during both healthy and fault operations. Finally, the simulation and experimental results for an FPFTPM prototype are offered to verify the feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]

In order to enhance motor torque performance of existing two-phase 8/10 E-Core SRM, an improved modular permanent magnet (PM)-assisted Switched Reluctance Motor (SRM) structure is presented. Firstly, basic structure and operation principle of the proposed structure are introduced. To further evaluate performance improvement, effects of various parameters on the design such as inductance, flux-linkage, average torque and cogging torque are compressively investigated by finite element method (FEM) software subsequently. In the meantime, comparisons with other two-phase SRM structures are also performed including average torque, torque/PM volume, torque/ motor volume, torque/current, etc. Finally, a prototype is fabricated, and simulation and experimental results verify that the proposed design has high torque performance. [ABSTRACT FROM AUTHOR]

It is well known that permanent magnet Vernier machine (PMVM) has multiple flux field harmonics, which can produce stable torque. However, some flux field harmonics would create torque that undermines the total torque output. Such as the 6 slots 26 poles split-tooth PMVM here, of which modulated flux field outputs torque while fundamental flux field undermines torque output. In this article, a 26 pole PMVM with coding-shaped tooth is proposed. The coding-shaped tooth can introduce permeance harmonics with specific phase and amplitude, thus modulating flux fields that all output torque. Air-gap permeance harmonics of the proposed and the regular split-tooth PMVM are obtained via FEA. Based on MMF-permeance model, flux fields of two machines and their contributions to average torque are investigated, proving that the proposed machine has multiple flux fields that all output torque. Moreover, by optimizing geometric parameters of coding-shaped tooth, the proposed machine could obtain largest average torque and smallest torque ripple simultaneously. Electromagnetic performances of the optimized machines are studied comparatively in semianalytical way and FEA. It is proved that with same overall size, PM usage, and copper loss, the proposed machine could achieve 30% larger torque density, 86% smaller cogging torque, and 62% lower torque ripple than its counterpart. Finally, a 16-N·m (rated) prototype is built and tested. [ABSTRACT FROM AUTHOR]

The stator-PM machine concept has been practiced on the recently proposed stator-PM variable reluctance (VR) resolver. When inheriting the simple and sturdy rotor structure of the conventional VR resolver, the novel stator-PM VR resolver provides a chance to avoid the high-frequency excitation by the unique PM back electromotive force decoding solution. This article extends this stator-PM VR resolver category with the axial magnetic field technology. The axial slotless structure makes the VR resolver compact and much smaller than the radial field prototypes. The thin and light leaf-style rotor is suitable for the super-high-speed applications, as the additional inertia due to a sensor is not welcome in those scenarios. Additionally, the printed circuit board replaces the winding coils in the regular VR resolvers, significantly simplifying the manufacturing. The design with even and odd poles cannot share the same principle, so they are discussed separately. The prototypes with 4-X and 5-X configurations are tested in the experiment setup respectively to validate the analysis of the proposed structure. Moreover, the 4-X resolver is integrated with a permanent magnet synchronous machine, and a motor driver with the space vector modulation on the basis of the specific resolver decoder is built. [ABSTRACT FROM AUTHOR]

Acoustic noise and vibration sources in electric machines are mainly of electromagnetic and structural origin. A lumped structural unit response-based sensitivity analysis procedure is proposed in this article, which isolates electromagnetic and structural impacts brought by variation of different design parameters in a fractional slot concentrated winding, surface mounted permanent magnet synchronous machine (SPMSM). The impact of ten design parameters on average torque, torque ripple, synchronous inductance, dominant spatial-temporal order airgap force, cogging torque, friction torque, dominant mode frequency and structural unit response is studied in detail for a 12 slot/10 pole (12s10p) SPMSM. Analysis reveals that on a 12s10p SPMSM, slot opening has a very high impact on dominant airgap force component. A multilevel nonlinear regression model-based fast optimization strategy is introduced considering electromagnetic and structural design objectives and constraints following the sensitivity analysis. The optimized design is prototyped to validate the proposed design approach. Impact hammer-based modal analysis, no load, load and run-up tests are performed on the prototype for experimental validation. Ranging from structural tests to electromagnetic tests, the experimental results closely follow and validate the simulation-based predictions. [ABSTRACT FROM AUTHOR]

A dual-stator Vernier permanent magnet (DSVPM) machine is proposed in this article for improving the power factor. Compared with the conventional single-stator Vernier permanent magnet (SSVPM) machine with the surface-mounted permanent magnet rotor, the proposed DSVPM machine has the higher power factor and the overload capacity. The reason for the higher power factor and the overload capacity in DSVPM machines is explained theoretically in this article by air gap permeance theory, and the advantages of the power factor and overload capacity of DSVPM machine are verified by the finite element analysis (FEA) through 18-slots and 34-poles SSVPM and DSVPM FEA model. The rotor eddy current losses, core losses and magnet demagnetization ratio of the DSVPM and SSVPM machines are also studied in this article, the FEA results reveal eddy current and core losses and magnet demagnetization ratio are all lower in the proposed DSVPM machine. The power factor of DSVPM machine variation with the magnet thickness and pole ratio (the ratio of the rotor pole pair number to the stator pole pair number) is also researched by the theoretical and FEA methods. In this article, a surface-mounted permanent magnet machine with fractional-slot concentrated-winding is designed to compare the torque density and cost with DSVPM machine. The sandwiched rotor structure of the proposed DSVPM machine is discussed and the structural analysis by three-dimensional FEA is carried out to prove the feasibility of rotor support, the result reveal that the rotor structure has the sufficient strength. [ABSTRACT FROM AUTHOR]

This article proposes and investigates two asymmetric consequent-pole hybrid excited flux reversal machine (AS-CP-HEFRM) topologies, which have same numbers of iron poles and permanent magnets (PMs) with concentrated ac and dc windings on each stator pole and a salient pole rotor. If PM number on one stator pole is larger than 1, PMs are magnetized radially in the same direction on one stator pole, while opposite on adjacent stator poles. The phenomenon of the phase shift between the flux linkages of dc and PM excitations in the AS-CP-HEFRMs is revealed for the first time, which will weaken the regulation of dc excitation field to PM produced field. The elimination condition of the phase shift is derived and verified by finite-element analysis in this article, which can be considered as design guidelines in AS-CP-HEFRMs. Airgap magnetic field space harmonics of AS-CP-HEFRM are also investigated and verified by finite-element analyses. Meanwhile, the relationship between the rotor pole number and the stator pole arc (PM ratio) is derived and verified by global optimization based on genetic algorithm for maximum average torque. The influence of stator/rotor pole number combinations is also studied and compared in terms of torque, torque ripple, and flux regulation capability. The torque components produced by airgap magnetic field space harmonics are calculated and compared. A prototype has been built and tested to validate the finite element calculations. [ABSTRACT FROM AUTHOR]