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ABSTRACTSwarming is a macroscopic phenomenon in which surface bacteria organize into a motile population. The flagellar motor that drives swarming in Pseudomonas aeruginosa is powered by stators MotAB and MotCD. Deletion of the MotCD stator eliminates swarming, whereas deletion of the MotAB stator enhances swarming. Interestingly, we measured a strongly asymmetric stator availability in the wild-type (WT) strain, with MotAB stators produced at an approximately 40-fold higher level than MotCD stators. However, utilization of MotCD stators in free swimming cells requires higher liquid viscosities, while MotAB stators are readily utilized at low viscosities. Importantly, we find that cells with MotCD stators are ~10× more likely to have an active motor compared to cells uses the MotAB stators. The spectrum of motility intermittency can either cooperatively shut down or promote flagellum motility in WT populations. In P. aeruginosa, transition from a static solid-like biofilm to a dynamic liquid-like swarm is not achieved at a single critical value of flagellum torque or stator fraction but is collectively controlled by diverse combinations of flagellum activities and motor intermittencies via dynamic stator utilization. Experimental and computational results indicate that the initiation or arrest of flagellum-driven swarming motility does not occur from individual fitness or motility performance but rather related to concepts from the “jamming transition” in active granular matter.IMPORTANCEIt is now known that there exist multifactorial influences on swarming motility for P. aeruginosa, but it is not clear precisely why stator selection in the flagellum motor is so important. We show differential production and utilization of the stators. Moreover, we find the unanticipated result that the two motor configurations have significantly different motor intermittencies: the fraction of flagellum-active cells in a population on average with MotCD is active ~10× more often than with MotAB. What emerges from this complex landscape of stator utilization and resultant motor output is an intrinsically heterogeneous population of motile cells. We show how consequences of stator recruitment led to swarming motility and how the stators potentially relate to surface sensing circuitry.

Abstract The magnetic saturation of iron‐core will reduce the maximum output force, influence the linear force characteristic and control precision of the magnetic bearing. To avoid these problems, a modified iron‐core design rule for the alternating‐pole magnetic bearing is proposed. The thickness of both stator yoke and rotor journal should be designed as 3/4 of the stator pole width for the alternating‐pole configuration, which is successfully verified by 3D finite element method and experiments. Based on the improved design, the structural sizes, rotor iron losses, and force coupling characteristics of the paired‐pole configuration and the alternating‐pole configuration are compared. The results show that the size of the alternating‐pole bearing is smaller than that of the paired‐pole bearing; the alternating‐pole configuration generates slightly higher rotor iron loss than the paired‐pole configuration; the coupling strength of the alternating‐pole configuration is stronger than that of the paired‐pole configuration irrespective of whether the magnetic force coupling is caused by rotor displacements or control currents. The presented method and results can provide a reference for the design and selection of the active magnetic bearings.

Abstract Inter‐turn faults are most commonly the initial stator winding fault in power trains with Voltage Source Inverters. Without counteractions, these faults can propagate and cause catastrophic failures in safety critical applications like all‐electric aircraft. The propagation of an inter‐turn fault can be reduced, by limiting the local temperature at the fault. In this article, a fault tolerant control scheme is designed and validated, which reduces the heat of an inter‐turn fault by a controlled adaption of the operating point. The control strategy utilizes the hyperbolas of constant torque and the controller design is based on a linear time‐invariant system description. A machine learning regression is used for the online heat estimation and a 3D lumped‐parameter model to evaluate the thermal effectiveness. To test the control scheme, an inter‐turn fault is actively switched, which generates the local heat equal to 13% of the overall stator copper losses. The control scheme adopts the operating point within 30 electric periods, which reduces the generated heat of the inter‐turn fault by 70%. This causes a temperature reduction at the fault locally from 367°C to 175°C, which extends the approximated insulation life from 30 s to 5000 h.

Abstract The three‐phase permanent magnet synchronous motor (three‐phase PMSM) has gained much popularity in many applications due to its various advantages. In addition, due to the good fault tolerance, simple inverter circuit structure and high torque density, the six‐phase PMSM has better prospects than three‐phase PMSM in biomedical devices, electric vehicles and other fields with high reliability requirements. In this study, a six‐phase axial‐flux PMSM inherently without cogging torque is proposed to improve torque density, which equips the 60° phase‐belt toroidal winding (60°TW) and slotless stator core. Based on the same effective volume, permanent magnet material, power grade and the other major motor parameters, two six‐phase PMSMs with 30° phase‐belt toroidal winding (30°TW) and 60°TW are designed, respectively. The armature reaction field, air gap magnetic density, back‐electromotive force, output torque, loss characteristic and torque‐speed characteristic are compared by using three‐dimensional (3D) finite‐element models in detail. Finally, the experimental test is carried out using the prototype of three‐phase PMSM with 120° phase‐belt toroidal winding. The experimental results indirectly verify the feasibility of 60° phase‐belt toroidal winding and correctness of 3D FEM. The 3D FEM analysis results are presented to show that torque density of the proposed six‐phase PMSM with 60°TW is improved in comparison to the six‐phase PMSM with 30°TW. Index Terms—60° phase‐belt toroidal winding, axial flux, six‐phase permanent magnet synchronous motor, torque density

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.

ABSTRACT In the soil bacterium Pseudomonas putida, the motor torque for flagellar rotation is generated by the two stators MotAB and MotCD. Here, we construct mutant strains in which one or both stators are knocked out and investigate their swimming motility in fluids of different viscosity and in heterogeneous structured environments (semisolid agar). Besides phase-contrast imaging of single-cell trajectories and spreading cultures, dual-color fluorescence microscopy allows us to quantify the role of the stators in enabling P. putida’s three different swimming modes, where the flagellar bundle pushes, pulls, or wraps around the cell body. The MotAB stator is essential for swimming motility in liquids, while spreading in semisolid agar is not affected. Moreover, if the MotAB stator is knocked out, wrapped mode formation under low-viscosity conditions is strongly impaired and only partly restored for increased viscosity and in semisolid agar. In contrast, when the MotCD stator is missing, cells are indistinguishable from the wild type in fluid experiments but spread much more slowly in semisolid agar. Analysis of the microscopic trajectories reveals that the MotCD knockout strain forms sessile clusters, thereby reducing the number of motile cells, while the swimming speed is unaffected. Together, both stators ensure a robust wild type that swims efficiently under different environmental conditions. IMPORTANCE Because of its heterogeneous habitat, the soil bacterium Pseudomonas putida needs to swim efficiently under very different environmental conditions. In this paper, we knocked out the stators MotAB and MotCD to investigate their impact on the swimming motility of P. putida. While the MotAB stator is crucial for swimming in fluids, in semisolid agar, both stators are sufficient to sustain a fast-swimming phenotype and increased frequencies of the wrapped mode, which is known to be beneficial for escaping mechanical traps. However, in contrast to the MotAB knockout, a culture of MotCD knockout cells spreads much more slowly in the agar, as it forms nonmotile clusters that reduce the number of motile cells.

Abstract This study proposes a method to reduce the electromagnetic noise of a double‐layer interior permanent magnet synchronous motor (DIPMSM) by optimising the flux barrier. First, a noise prediction model of the 36‐slot/8‐pole DIPMSM is established by finite element (FE). According to the simulation results, the noise of the motor is the loudest at 5000 rpm, especially with a noise component of 3333.3 Hz. From the results of modal analysis, it can be concluded that the four‐order radial force with a frequency of 3333.3 Hz resonates with the stator, resulting in the loudest noise. Then, the source of the radial force that causes the loudest noise is analysed, and it can be found that the 9th and 11th harmonics of rotor magnetic motive force have the greatest contribution to the force. By optimising the rotor, the radial force contributed by the 9th and 11th harmonics is weakened, thereby reducing the noise caused by these harmonics. Finally, the electromagnetic performance and noise of the optimised motor are checked by FE. Compared with the initial rotor, the torque ripple is reduced by 26.79%, and noise is reduced by 5.542 dB. The noise test on the prototype verifies the accuracy of the noise prediction model.

Abstract Synchronous generator (SG) plays a vital and critical role in the power system by supplying electric power to consumers. Various faults in SGs can cause some catastrophic events such as power disruption or blackout. These faults can be classified into two electrical and mechanical faults. Short circuit in stator windings and field winding are electrical fault while bearing, static/dynamic eccentricity, and broken damper bars faults are mechanical one. Unlike the induction machines, there are no much researches in SGs condition monitoring owing to its complex behaviour against the faults. Herein, the SG modelling approaches are presented briefly to elaborate shortcoming and challenging issues in the modelling, and then a comprehensive review of various electrical and mechanical fault detection methods is presented.

Abstract As one of the most important assets of the industry, it is crucial to fully characterise all failure modes showing potential to degrade the normal operation of induction motors (IMs). One of the failure modes which lacks detailed knowledge and proper diagnostic tools is the inter‐turn short‐circuit (SC) fault. Given the severity of such failure mode, it is pivotal to ensure that incipient fault symptoms are correctly identified, thus preventing critical damages to the IM. Unfortunately, the state‐of‐the‐art does not provide enough data to confirm whether the available diagnostic tools act out in due time to avoid permanent damage to the faulty IM. To evaluate the impacts of this failure mode in the temperature of the stator windings of an IM, this paper presents the results obtained from two alternative thermal models of the same IM, resorting to the lumped parameter thermal network method and to the finite elements method. The results confirm that diagnostic tools reported in the literature might not be effective, failing to correctly diagnose an inter‐turn SC fault and to warrant the lead time required to take actions suitable to prevent permanent damage to the IM.

In this study, an integral sliding mode control approach for controlling the power electronics converters of a doubly-fed induction generator (DFIG) wind turbine system is presented. The power electronics interface consists of back-to-back converters. The rotor side converter regulates the active and reactive powers at the DFIG stator through controlling the stator currents. The stator current dynamics, with respect to the rotor voltages, is developed from the conventional equations of the DFIG model. In this control configuration, the knowledge about the rotor currents is not required, which reduces the use of the current measurement sensors. The grid side converter ensures constant dc-link voltage while transferring the power from the DFIG rotor to the grid. The proposed control approach uses a composition of sliding mode and integral parts to improve the overall performance and robustness against parametric variations and uncertainties. A lab-scale DFIG wind turbine system is used to investigate the proposed control approach efficiency under various operating conditions. The experimental results show the effectiveness of the proposed control approach in achieving control objectives to operate the DFIG wind turbine system.

This study analyses a double Y shaft 30° winding for six-phase fault-tolerant permanent magnet synchronous motors and introduces a novel modular 18-slot stator topology used in high-performance electric vehicles with unequal teeth width and unequal slot size. The new topology adopts double-layer winding in the same phase and single-layer winding in the adjacent phase. Additionally, two new pole/slot combinations for the six-phase motor, 18-slot/10-pole and 18-slot/14-pole, are proposed by analysing the air-gap flux harmonics that are produced by the stator winding. In addition, the optimal design of the 18-slot/10-pole motor is determined by using the average torque and the torque ripple as indexes. The motor can run continuously in the range of 0–4 times the rated speed with a one-time short-circuit current, a high isolation capability in the different phases and a high efficiency. The final parameters and performance of the 18-slot/10-pole motor are provided.

High silicon (Si) electrical steel has the potential for efficient use in applications such as electrical motors and generators with cost-effective in processing, but it is difficult to manufacture. Increasing the Si content beyond 3 wt.% improves magnetic and electrical properties, with 6.5 wt.% being achievable. The main goal of this research is to design, develop, and implement a scalable additive manufacturing process to fabricate Fe with 6.5 wt.% Si (Fe–6Si) steel with high magnetic permeability, high electrical resistivity, low coercivity, and low residual induction that other methods cannot achieve because of manufacturing limitations. Binder jet additive manufacturing was used to deposit near net shape components that were subsequently sintered via solid-state sintering to achieve near full densification. Here, it is shown that the use of solid-state sintering mitigates cracking since no rapid solidification occurs unlike fusion-based additive technologies. The Fe–6Si samples demonstrated an ultimate tensile strength of 434 MPa, electrical resistivity of 98 μΩ cm, and saturation magnetization of 1.83 T with low coercivity and high permeability. The results strongly supports to replace the only available 0.1 mm thick chemical vapor deposition (CVD) produced Si steel using the cost effective AM method with good mechanical and magnetic properties for motor applications.

Dielectric response analysis, performed in time domain and frequency domain is one of the interesting methods used for condition assessment of high voltage equipment. In this article, the degradation of epoxy-mica composite insulation which is widely used in rotating machines has been investigated through frequency domain spectroscopy measurements. Artificial ageing of the carefully prepared stator bar insulation sample was performed through simultaneous application of high temperature and electric field in a designated environmental chamber for specific durations. To study the effect of temperature, the measurements were performed at temperatures ranging from 20 to 60°C at different ageing status. Following experimental work, the measurement results were modelled using Havriliak–Negami model and ageing sensitive parameters were extracted. To study the effect of temperature, the measurements were performed at temperatures ranging from 20 to 60°C. The modelled results matched well with the experimental measurements and certain model parameters sensitive to the ageing condition were identified. The numerical relationships between the insulation status of the stator bar and the aforementioned parameters were identified. It was observed that the nature of the numerical relationship remains identical in the investigated temperature range, although the coefficients vary to some extent.

This study studies, using experimentally verified finite element (FE) analysis, various performance measures of the brushless doubly fed induction generator (BDFIG) when magnetic wedges are used for closing stator open slots. The BDFIG is an attractive generator solution for offshore wind power and can replace doubly fed slip-ring induction generators. It is shown in this study that the use of magnetic wedges, commonly used in large induction machines, reduces the stator windings magnetising currents in a BDFIG, reflected in the values of magnetising inductances. They also increase the leakage flux in the stator slots, leading to a larger series inductance in the equivalent circuit. The series inductance significantly affects the BDFIG performance as well as the rating of its converter. The effects of magnetic wedges on BDFIG air-gap flux, synchronous torque, and stator tooth top saturation is also investigated. Two-dimensional FE analysis of an experimental 250 kW BDFIG is used in this study, verified by experimental measurements.

ABSTRACT Bacteria sense chemicals, surfaces, and other cells and move toward some and away from others. Studying how single bacterial cells in a population move requires sophisticated tracking and imaging techniques. We have established quantitative methodology for label-free imaging and tracking of individual bacterial cells simultaneously within the bulk liquid and at solid-liquid interfaces by utilizing the imaging modes of digital holographic microscopy (DHM) in three dimensions (3D), differential interference contrast (DIC), and total internal reflectance microscopy (TIRM) in two dimensions (2D) combined with analysis protocols employing bespoke software. To exemplify and validate this methodology, we investigated the swimming behavior of a Pseudomonas aeruginosa wild-type strain and isogenic flagellar stator mutants (motAB and motCD) within the bulk liquid and at the surface at the single-cell and population levels. Multiple motile behaviors were observed that could be differentiated by speed and directionality. Both stator mutants swam slower and were unable to adjust to the near-surface environment as effectively as the wild type, highlighting differential roles for the stators in adapting to near-surface environments. A significant reduction in run speed was observed for the P. aeruginosa mot mutants, which decreased further on entering the near-surface environment. These results are consistent with the mot stators playing key roles in responding to the near-surface environment. IMPORTANCE We have established a methodology to enable the movement of individual bacterial cells to be followed within a 3D space without requiring any labeling. Such an approach is important to observe and understand how bacteria interact with surfaces and form biofilm. We investigated the swimming behavior of Pseudomonas aeruginosa, which has two flagellar stators that drive its swimming motion. Mutants that had only either one of the two stators swam slower and were unable to adjust to the near-surface environment as effectively as the wild type. These results are consistent with the mot stators playing key roles in responding to the near-surface environment and could be used by bacteria to sense via their flagella when they are near a surface.

This study proposes a novel method for detecting faults in the stator of the doubly-fed wind turbines based on the combination of singular value decomposition (SVD) filtering and least-squares parameter invariant signal technique (TLS-ESPRIT). The stator current signal and rotor current signal are simulated in the form of stator inter-turn short-circuit fault, and TLS-ESPRIT performance test is carried out. The results show that TLS-ESPRIT still has a high-frequency resolution for a short-time signal with high-frequency resolution and can accurately estimate the frequency of each part of stator current. This method can effectively shorten the sampling signal's tempo, the performance of its parameter estimation is also superior.a

Wind energy conversion systems (WECSs) require a suitable control to maximise the power generated by wind turbines independently on the wind conditions. Variable-speed fixed-pitch wind turbines with doubly-fed induction generators (DGIG) are used in WECSs for their higher reliability and efficiency compared to variable-pitch wind turbine systems. This study proposes an effective control algorithm to maximise the efficiency of fixed-pitch wind turbines with DFIGs using particle swarm optimisation control to compensate for the errors in the estimation of the circuit parameters of the generator. The proposed control algorithm generates an optimal speed reference to optimise the mechanical power extracted from the wind and the optimal d-axis rotor current through stator reactive power management to minimise the electrical losses of the doubly-fed generator. The optimal speed reference is provided by a maximum power point tracking control below the rated wind speed and a soft-stalling control above the rated wind speed, while the optimal d-axis rotor current is searched by a particle swarm optimisation algorithm. The proposed control system has been verified by numerical simulations and it has been demonstrated that the energy generated for typical wind speed profiles is greater than that of a traditional control based on a model-based loss minimisation.

This study proposes a fault-tolerant matrix-converter-controlled IPMSM-drive system, in which a predictive speed-loop controller and a predictive current-loop controller are implemented to improve its dynamic responses, including transient responses and load disturbance responses of the IPMSM-drive system in both normal and faulty conditions. In addition, a sliding-mode estimator is used to estimate the rotor position, rotor speed, and stator currents of the IPMSM when the encoder or current sensor in the IPMSM-drive system is faulty. As a result, the IPMSM-drive system allows for either an encoder fault or a Hall-effect sensor fault. The detailed fault detection, diagnosis, and control are discussed here. In case of an encoder fault or a Hall-effect current sensor fault, the IPMSM-drive system still functions. A digital signal processor, TMS 320LF2407A, is used as a control centre to execute the fault-tolerant algorithm, state-estimating algorithm, and control algorithm. Experimental results can validate the correctness and feasibility of the proposed fault-tolerant and predictive control methods.

This article proposes a new topology of double-sided linear Vernier permanent magnet (LVPM) machine with segmented translator structure. A combination of a typical Halbach array consists of two horizontally magnetised permanent magnets (PMs) sandwiched between a salient iron tooth and adjacent vertically magnetised PM pole with the aim of improving its electromagnetic performance. The coreless partitioned translator contributes to a significant reduction in mass and the associated cost. With the aid of finite element analysis (FEA), two LVPM machines with the same PM, and stator volume have been investigated, analysed, and compared. The results imply that the proposed LVPM is capable of producing higher force density, while it exhibits lower cogging force and force ripple compared to its counterpart.

Here, static and dynamic (rotating) misalignments between the low-speed rotor (LSR) and the stator of axial flux magnetically geared machines are studied with the aid of 3-D finite element analysis (FEA). The influence of rotor/stator axis misalignments on machine performance in terms of cogging torque, air-gap flux density, and back-EMF is investigated with reference to the fully healthy condition. The results show that the LSR and HSR cogging torques are significantly affected by such misalignments due to distorted air-gap flux density. However, the amplitude and the harmonics of the back-EMF are only slightly changed. Furthermore, the influence of the misalignments on the machine torque performance is investigated. It is shown that the machine torque is significantly reduced when the LSR axis is misaligned with the axis of the stator. Thus, it is concluded that the torque performance of axial flux magnetically geared machines significantly deteriorates under static and dynamic axis misalignments. In addition, the two types of misalignments have similar effects on machine performance.

Providing additional damping for system electromechanical oscillations through doubly fed induction generator (DFIG)-based wind turbines is investigated in this study. In this regard, first an objective function is developed to tune the DFIG control gains, aim to maximise the wind farm (WF) contribution to system oscillation damping, but it is shown that it causes a decrease in the damping of DFIG stator mode. In other words, with the current DFIG control design, it is not possible to improve both the small signal stability of the power system and the dynamic stability of WF together. Afterwards, two high-pass filters are suggested to be employed in the control design of DFIG. It is shown that with the modified control design, it is possible to improve the system oscillation without spoiling the dynamic stability of the WF itself. Eigenvalue analysis is performed to validate the effectiveness of the modified control design.

This study presents a comparative study of different modular brushless wound rotor synchronous machines (MB-WRSM) using non-overlapping fractional slot double-layer concentrated windings. The goal of the study is to highlight the structure which offers the best fault-tolerance capability and the highest output performance. The fundamental winding factor is calculated by using the method based on voltage phasors as a significant criterion to select the preferred numbers of phases, stator slots, and poles. With the limited number of poles for a small machine (3.67 kW/7000 rpm), 15 different machines for different phase/slot/pole combinations are analysed using two- dimensional (2D) finite element method and compared according to three criteria: torque density, torque ripple, and machine efficiency. The seven-phase/seven-slot/six-pole machine is chosen with the best compromise of high torque density, small torque ripple (3.89%), and high nominal efficiency (95%). This machine is then compared with a reference design surface-mounted permanent magnet synchronous machine (SM-PMSM). The simulation results are discussed and demonstrate that the MB-WRSM presents interesting performance features, such as extended field weakening range, with overall performance closely matching that of an equivalent SM-PMSM.

This study deals with a novel control strategy for permanent magnet synchronous machines (PMSMs) to incorporate disturbance compensation features in the existing current controller maintaining at the same time the integrity of the reference tracking performances. The torque produced by a PMSM arises from the interaction of stator currents and rotor magnetic flux, therefore an intrinsic disturbance is propagated to the output, in case the flux is not perfectly sinusoidal. In particular, the authors focus is to propose the effective correction of undesired harmonic effects generated on the torque from the non-ideal machine rotor. With the knowledge of the back electromagnetic force waveform, it is possible to determine the current waveforms necessary to produce a smooth torque in normal operation and through model-base considerations, the required voltage harmonic waveforms are also computed. The method is also extended to the flux weakening operation of the machine. The analytical solutions found are used in place of the classical αβ/dq transformations, without modifying the field-oriented control performance of the main controller. The effectiveness of the proposed control scheme is verified by means of test-bench measurement.

The next-generation integrated drive (NGID) is an 80 kW demonstrator showcasing the latest innovations in high power density electric drive technology. A prototype 30 krpm maximum speed permanent magnet synchronous machine for an automotive traction application is under construction. This study describes several aspects of the detailed design and how these fit together in the complete drive package to increase the power density of the NGID.

This paper compares the short-circuit performance of superconducting (SC) generators with three different topologies, i.e. iron-cored stator and rotor, iron-cored stator and air-cored rotor, and air-cored stator and rotor. The analysis is based on three-phase short-circuit fault, and finite element analysis is used for simulation. Following the introduction of specifications of generators, the short-circuit performances of different topologies are analysed and compared, with the field winding excited by voltage and current excitation sources, respectively. It shows that the short-circuit performance can be improved by limiting the field current.

Rotor electrical faults are an issue frequently encountered when applying condition monitoring and fault diagnosis on induction machines. The detection via the analysis of the stator current becomes challenging when the rotor cage suffers from multiple breakages at non-adjacent positions. In that case, electromagnetic asymmetries induced by the broken bars can be masked in such a way, that the diagnostic ability is highly likely to be obscured, thus leading to misinterpretation of the monitored signals' signatures. A new approach is proposed in this work to overcome this problem while the motor is at steady state. In this study, an industrial 6.6 kV, 1.1 MW induction motor is simulated with finite element analysis (FEM) and its electromagnetic variables are analysed and studied under healthy state and several faulty conditions. The analysis of the stator current and stray flux waveforms is executed in both the transient and the steady state and aims to diagnose the challenging cases where the rotor breakages are non-consecutive with regard to their spatial location. The results show the potential of flux analysis to fault severity regardless of the spatial position of the broken bars.

The study of stator core vibrations generated by electromagnetic forces in electrical machines is of great practical and theoretical interest. An important part of the problem is the correct determination of mode shapes and eigen frequencies of the mechanical system. This work brings to discussion a new experimental modal analysis (EMA) method developed for synchronous machines in which the traditional instrumented hammer impulse is substituted by a magnetic pulse generated by currents applied in two poles. Experimental results obtained in a real 190 MVA hydrogenerator are shown.

This study discusses the topology development of a cylindrical transverse flux linear machine for use with a free piston engine. Despite its three-dimensional flux path, the stator of this topology can be made from regular laminated components and only the translator includes soft magnetic composites. The detailed design development is discussed, including stator tooth combination, alternative winding, and fabrication techniques. Results from both finite element analysis and experimental measurement are compared, which gives a validation of the feasibility of the building process.

Here, a multi-physics approach is presented for the design optimisation of an integrated modular motor drive (IMMD). The system is composed of a modular permanent magnet synchronous motor (PMSM) and a GaN-based modular motor drive power stage. The multi-physics model includes motor drive inverters and DC-link capacitor bank (electrical model), stator windings and rotor magnets (electromagnetic model), heat sink (thermal model), and a geometrical model. The main purpose of the design optimisation is to obtain the highest power density possible, which is quite critical in integrated drives. Due to the integrated structure, the system has several interdependencies and parameters are selected based on those relationships. An 8 kW IMMD system design is proposed from the developed optimisation tool and evaluated. The resultant system has a power density of 0.71 kW/lt, drive efficiency of 98.3%, and motor efficiency of 96.6%.

The thermal design-analysis of devices with electrical windings impregnated using varnish materials is frequently challenging. This is due to difficulties in predicting theoretically the equivalent thermal properties for the composite materials, such as impregnated windings, in a reliable manner. The existing approach makes use of the impregnation ‘goodness’ factor, which allows for imperfections associated with the winding impregnation to be accounted for. This, however, requires experimentally derived data from appropriate material samples or machine assemblies. Considering relatively large range of commercially available varnishes, such data are often limited and are not readily accessible. In this investigation, a set of three alternative varnish materials commonly used in impregnation of low-voltage electrical windings has been evaluated. To provide better understanding of the material impregnating properties, data from multiple impregnations are also provided. The experimental findings have been supplemented with theoretical analysis on the impregnation ‘goodness’ and stator-winding contact thermal resistance for a selected winding construction. To highlight the importance of appropriate input thermal material data, a case study machine design is thermally analysed.

An induction machine with combined star-delta stator winding is analysed by means of numerical simulations based on lump parameter and finite element method (FEM) models. The use of combined star-delta winding may lead to suppressing selected higher spatial harmonics of the magnetic flux density in the air gap and, thus, to lowering the energy losses and improving the energy efficiency of the machine.

Here, machines having permanent magnets (PM) mounted in the stator are compared during fault operations such as armature winding short circuits. The magnet potential irreversible demagnetisation is also investigated due to the fact that the PMs are placed close to the armature coils (heat sources) and hence are prone to temperature-related demagnetisations. It is found that the doubly salient and flux reversal machines have inherently higher fault tolerant capabilities when compared with the switched-flux one. To the point of view of demagnetisation withstand capability, the doubly salient topology stands out as the most robust one while the switched flux is the weakest one.

The doubly fed induction generator (DFIG) has become increasingly popular for variable speed wind turbines because of the lower power electronics converter rating required. However, the small air gap of a DFIG causes it to be vulnerable to slight misalignment of the rotor which may cause a large unbalanced magnetic pull (UMP) to be exerted on the bearings. The reliability of the generator is important to reduce revenue loss; this is especially the case for generators in offshore wind turbines where minimising the cost of energy is crucial in completing with more established forms of electricity generation. This study has proposed the usage of stator damper windings to reduce the UMP. An example of a four-pole DFIG with static eccentricity is shown where finite element analysis is used to verify the UMP for cases with and without damper windings. Finally, additional losses due to rotor eccentricity are discussed.

This paper presents an approach to noise, vibration and harshness (NVH) analysis suitable for electro-mechanical rotating systems, whereby both the electrical and mechanical sources of excitation are included and the response of the system is calculated. Focus is placed on modelling methods for the stator structure. The stator is considered to be a transversely isotropic structure and the effect that material properties can have on dynamic response is presented for a stator, both in isolation and in the full drivetrain model. NVH predictions are shown for a full drivetrain model of a prototype EV city car and compared to test data, demonstrating good correlation between test results and simulation with the described method.

The TC48 drive is a low-cost, low-voltage integrated motor-drive solution suitable for mild hybrid electric vehicles, off-highway traction, and any application where a compact, highly torque-dense machine is required. Low-voltage solutions for electric vehicles are attractive to manufacturers due to lower insulation requirements, and hence lower cost. The package is based on a six-phase switched reluctance machine, which uses a novel stator topology and unique winding design to achieve high torque density. The power electronics converter hardware is integrated into the motor housing, giving a physically, electrically, and thermally optimised solution. The complete package has been designed to be suitable for manufacturing in high volumes. This study describes the electromagnetic design of the motor, the mechanical innovations used to physically realise this design, and the cooling system which makes the high power density possible. The integration of the power electronics and their control is also discussed. The project is the result of collaboration between Newcastle and Loughbosrough Universities, RDM Ltd., Productiv, Infineon, Tata Steel, and Libralato.

This study addresses double-sided stationary stators in a linear electric generator with similar operation to a linear oscillatory motion electric machine. The plate mover in the linear electric generator's double-sided stationary stators is powered by the acoustic power output of the thermoacoustic engine's acoustic line. The main originality of this structure resides in the linear guidance used for the moving part. The mover is made up of a plate of sandwich magnets between two stators. This plate is in magnetic balance between the two stators through a controlled friction device.

The effect of tooth tips on the performance variations due to using grain-oriented electrical steel (GOES) stator laminations in permanent magnet fractional-slot modular machines is studied in this work. It is concluded that the electromagnetic performance is further improved using GOES in machines with tooth tips compared to machines without tooth tips. This is due to a higher increment on the flux density in the airgap. The acoustic behaviour variations due to using GOES are predicted by analysing several mechanical- and acoustic-related parameters. It is predicted that implementing GOES improves the acoustic behaviour in machines without tooth tips. Furthermore, the effects of GOES in machines with tooth tips are slightly improved compared to machines without tooth tips. However, in order to determine the real mechanical and acoustic behaviours, further analysis is needed.

Here, the influence of stator slot and rotor pole combination on performance of flux reversal permanent magnet (FRPM) machine with consequent-pole permanent magnet (CPM) structure is analysed. First, for 12-slot FRPM machines, the torque capabilities of CPM and conventional surface-mounted PM (SPM) structure having different rotor poles are compared. It shows that the torques of CPM machines are largely affected by the rotor pole number while the torques of SPM machines are similar. This is further explained by the equivalent pole-pair number and corresponding saturation condition. The influence of stator slot number and PM width ratio on torque performance of the CPM-FRPM machine is then investigated. Finally, detailed electromagnetic performance of the 12/14 SPM- and CPMFRPM machine is analysed and compared.

This paper presents a low-cost approach to experimentally characterise the effect of the inverter supply on the losses in an electrical machine. The set-up comprises of representative subassemblies of the stator and winding, referred to as ‘motorettes’, and a single phase, fast switching silicon-carbide-based converter. The sub-assembly-based thermal analysis has been shown to be a time and cost-effective method to examine winding loss, over a range of operating conditions. In addition to the slot to stator thermal resistance and capacitance. This provides critical information for thermal model calibration and produces more accurate thermal and loss predictions of the full machine behaviour. A test arrangement has been devised to replicate the magnetic excitation of the electrical machine stator during normal operation. This builds upon previous techniques, to allow iron loss to be investigated. Through multiple tests using DC, AC, and PWM-AC supplies, a 20% increase in iron loss is observed due to PWM effects.

Engineers are constantly developing different ways to cool electrical machines more efficiently. Ventilation ducts/channels are common in the stators of large electrical machines. Lately ventilation ducts on rotors of electrical machines are also being introduced. While measurement of fluid velocities inside stationary ventilation ducts, such as those present in and around the stator core of electrical machines, are relatively easy, measurement of fluid velocities inside rotating ventilation ducts, such as those present on the rotors of electrical machines, is quite challenging. This study describes a method which enables the measurement of fluid velocities inside rotating ducts on the rotor of electrical machines.

High temperature superconductors (HTS) enable very compact electric machines with high power density. Here, an HTS power generator based on authors’ previous double claw pole design is studied and improved. The original design of the double claw pole machine features a stationary field core to provide support and access to the superconducting field winding and its cryostat. It does not serve any other purpose. However, a homopolar field passes through it. The improvement was made to replace the field core by iron-cored copper coils, creating an inner stator within the generator to increase the electric loading. Through this step, the power output of the generator was increased from 10 to 11.6 MW, increasing the power density from 54.28 to 63.54 W/kg while maintaining the same outer diameter.

This study proposes a technique for arbitrary current sharing between winding sets of any multiple three-phase machine by using a decoupled control in two-dimensional orthogonal vector space decomposition subspaces. With ability to arbitrarily set the d–q currents in all winding sets, both active and reactive power of each winding set can be arbitrarily set as well. Normally, this behaviour requires machine model in multi-stator variables where control implementation may be challenging due to the cross-coupling between winding set variables. On the contrary, in this study, the correlation between multi-stator and the vector space decomposition modelling has been used so that benefits of both modelling approaches are fully utilised: a decoupled control feature thanks to vector space decomposition and an ability to individually control winding set currents, a feature of the multi-stator modelling approach.

This study introduces the development of the straight pole four-phase double-stator switched reluctance machine (SRM) which is considered to provide high torque density and low copper loss. The basic concept behind this design is to combine the features of the mutually coupled SRM and the double-stator SRM. In this study, the analytical method alongside the 2D finite element method (FEM) verification would be presented to reveal the developing path. Moreover, to verify the proposed SRM concept, the prototype machine has been designed and built. The performance result from 2D FEM is presented.

The authors built a prototype motor with NANOMET stator cores. NANOMET is one of the several nanocrystalline soft magnetic alloys [see ref. 1]. Motor iron loss and other characteristics were compared with 35A360 (Japanese Industrial Standards), which is one of the widely used conventional electromagnetic steel sheet, and the effectiveness of the new material is shown. This study describes the method to build NANOMET stator cores, and presents the evaluation results of the prototype motor.

With the growth of wind energy penetration in electricity transmission grids, fault ride-through (FRT) ability is required in order to maintain the uninterrupted operation of wind farm in voltage disturbance scenarios. For widespread used doubly-fed induction generator FRT issues, an auxiliary hardware circuit is adopted in large-grid-voltage drop situations. Among all hardware protection devices, the rotor crowbar scheme can suppress rotor overcurrent immediately, while the stator series impedance scheme has the advantage of increasing voltage during voltage dips. A comprehensive FRT scheme based on series impedance and rotor crowbar is proposed. Also, the simulation results show that the proposed method can keep the continuous operation of wind farm during fault situation and recovery, also suppress the overcurrent during voltage recovery and improve the terminal voltage.

This paper presents a linear variable reluctance permanent magnet (LVRPM) machine where the armature winding and inset Halbach array permanent magnets (PMs) are mounted on E-core stators. The Halbach array consists of a vertically magnetised PM pole and a salient ferromagnetic iron pole (split tooth) sandwiched between two horizontal PMs. The translator consists solely of laminations with salient iron poles. As a variable reluctance machine, it exhibits inherent magnetic gearing and a higher force and power density than the conventional synchronous PM machines. Finite element analysis (FEA) has been used to investigate the effect of machine parameters. The logical development of the LVRPM from the more conventional Vernier Hybrid machine is presented, including a near 50% reduction in magnetic flux leakage and a higher flux per unit magnet mass.

The Hilbert–Huang transform (HHT) is a time-frequency signal analysis method based on empirical mode decomposition and the Hilbert transform. It is well suited for reliable fault detection since it is unaffected by transient conditions which might cause false alarms. The method has been demonstrated in recent years for bearing fault detection of induction machines (IM). This study explores the possibility of applying the technique to the detection of stator short-circuit faults in permanent magnet synchronous machine (PMSM). A method based on the online statistical analysis of the instantaneous frequency calculated by the HHT is proposed and demonstrated through real-time hardware-in-the-loop simulation and experimental results.

In this study, the influence of the stator and rotor geometric parameters on the rotor bar current waveform and performance characteristics of a squirrel-cage induction machine (IM), based on a slot/pole number combination (48-stator slot/8-pole/52-rotor slot), with the same winding layout, stator outer diameter, stack length, stator current, and rated speed as the Toyota Prius 2010 interior permanent magnet machine, is investigated. In order to reveal the individual influence of each parameter, parametric analyses have been conducted for each geometric parameter, and the corresponding variations of torque, torque ripple, power losses, and efficiency are numerically studied. It has been shown that in addition to rotor slot width, rotor slot depth, and stator slot width, corresponding to rotor tooth width, rotor tooth height, and stator tooth width, respectively, have a significant effect on the bar current waveform and performance characteristics while the slot opening widths have the least effect.

In this study, a novel partitioned stator hybrid excited machine is proposed, in which the excitation sources including both permanent magnets (PMs) and field windings are allocated on the secondary stator that is separated from the original stator having armature windings. As a result, the available space is boosted to improve the torque density and flux regulation capability. Meanwhile, the rotor is simple without coil or PM. The PMs on the stator is placed on the slot openings between the two neighbour tooth tips, with which the uncontrolled voltage of the proposed machine is limited and it is favoured for safety-critical applications. The machine topology and operating principle are introduced in detail, and the basic electromagnetic performance is evaluated based on finite element method to validate the analysis.