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A small-signal model based on the net flux method is developed for mutually coupled switched reluctance machines (MCSRMs) to facilitate the design and analysis of the current controller for the drive. The underlying methodology of using net flux allows MCSRM modeling on a per-phase basis which reduces the time involved in characterizing the motor and the number of machine model parameters. A comprehensive theory of modeling the machine and extracting the machine parameters with analytical derivations is provided. Furthermore, a complete design procedure and analysis for a proportional-integrator controller is presented. The derived MCSRM small-signal model is useful to evaluate the controller's current tracking performance, disturbance rejection capability, and response features over a wide speed range. Simulation analysis and experimental results for a 3 phase, 150 W, full-pitched MCSRM drive system are provided both for small-signal model validation and current controller performance evaluation. [ABSTRACT FROM AUTHOR]

Outer-rotor switched reluctance machines (SRMs) have drawn much attention as promising candidates for in-wheel direct-drive motors of future electric vehicles. This article presents a systematic performance comparison of three outer-rotor SRM topologies for in-wheel traction applications in terms of the specific torque, electromagnetic efficiency, torque ripple, radial force, and mechanical aspects. A generalized design optimization framework for SRMs is proposed to enable the fast evaluation of large numbers of designs generated from the differential evolution by incorporating an analytical current profile estimation into the transient finite element analysis. The relationship between the saliency ratio and converter volt-ampere rating is also discussed. The calculations are then benchmarked with the experimental results from an existing prototype. The effectiveness of the performance prediction method and the proposed optimization approach is validated. [ABSTRACT FROM AUTHOR]

Synchronous reluctance machine (SynRM) has been studied widely in order to reduce its high torque ripple and improve its low power factor. This article proposes a torque ripple reduction method for SynRM by defining a novel parameter-torque function. With the help of torque function, the optimal currents aiming to compensate torque harmonics are obtained. The advantage of the proposed method is that torque function can be obtained easily and torque ripple reduction can be achieved by a simple control method. For the purpose of verifying the proposed method, both simulations and experiments are performed. Finally, the influence of power supply and parameter uncertainty on the proposed method has also been discussed. [ABSTRACT FROM AUTHOR]

The improvement of the robustness of the performance of electrical machines in presence of neglected features, such as manufacturing tolerances and deviations in material properties and parameters, is increasingly demanded. The available optimization procedures do not account for manufacturing tolerances, leaving the decision process incomplete. The article proposes a methodology for the selection of the more robust design towards manufacturing tolerances among the best candidates, detected by an optimization procedure. Statistical tools for tolerance analysis and worst-case analysis are discussed and adopted for the scope. The proposed methodology is used to select a robust design with respect to torque ripple deviations due to geometric tolerances in the laminations of a Synchronous Reluctance Motor with fluid shaped barriers. The statistical performance analysis and the worst-case analysis provide an estimation of the performance deterioration in the presence of the tolerances in the manufacturing process. [ABSTRACT FROM AUTHOR]

Switched reluctance motors (SRMs) have a robust and simple structure, high reliability because of the absence of magnetic field source on rotor, low cost and simple cooling system. However, conventional SRMs confront with some challenges such as low mean torque, low torque density and high torque ripples. For wider applications of SRM, the above-mentioned drawbacks must be mitigated. One possible method is changing the structure of SRMs. In this article, a novel 12/14 three-phase SRM with connected C-core structure is introduced which has a short path for the main flux of stator teeth. This brings about core loss reduction. On the other hand, both teeth of the stator phase in C-core develop a positive torque during the movement of the rotor from the unaligned position to the aligned position; this enhances the torque, the mean torque and torque density of the proposed SRM, keeping the volume fixed. Finally, the proposed SRM was prototyped and tested and its torque/rotor angular position characteristic was measured. To verify the novelty and merits of the proposed SRM, its mean and peak torque, torque density, core losses and torque ripples were compared with those of an optimized 12/8 three-phase conventional SRM and a significant match was achieved. [ABSTRACT FROM AUTHOR]

Solid-rotor switched reluctance machines (SRM), having the rotor machined from a single piece of metal, are one of the few viable options for motoring and/or generation under harsh operating conditions, including high speeds, high shaft temperature, and corrosive environment. Apart from double saliency and high degree of magnetic saturation as in any SRM, significant core losses due to high eddy currents, even under static conditions, make the characterization and modeling of solid-rotor SRM challenging. The objective of this article is to understand the magnetic characteristics of a solid-rotor SRM through extensive experimental studies and to develop a stator-side model for the machine which adequately captures its magnetic behavior. First, the flux-linkage characteristics of the solid-rotor SRM under test are measured over a wide range of excitation conditions and rotor positions. Applying a computationally efficient decomposition technique on each set of experimental data, the measured winding current is resolved into magnetizing and core-loss components to obtain a stator-side model of the machine. The proposed model is useful to predict the winding current and core-loss under different excitation conditions, which is necessary for simulation and performance prediction. The proposed method is more accurate than the existing methods, while being simple and fast to implement. [ABSTRACT FROM AUTHOR]

This article proposes an online calibration strategy of sensorless position estimation for switched reluctance motors (SRMs) with parametric uncertainties. For conventional sensorless SRM drives, the voltage drops on power devices and the winding resistance changing with the current and temperature are neglected, which affects the accuracy of the estimated position. In this article, an inductance calculation scheme is proposed to improve the real-time position estimation with these parametric uncertainties. First, the calculation errors of the flux linkage and inductance are both investigated and the error correction of the estimated rotor position is analyzed in detail. Then, the inductance values of the current overlapped phases are calculated. The dc component of the phase inductance is online adjusted, where all three phase inductances can be easily obtained accordingly. Finally, the real-time rotor position is acquired by the coordinate transformation of the calculated three-phase inductance during the current overlapped region. Compared to conventional SRM sensorless drives, the error of the estimated position due to parametric uncertainties can be significantly reduced without pulse injection, extra hardware, and prestored flux linkage and inductance profiles. The simulation and experiments are carried out on three-phase and four-phase SRMs to validate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Switched reluctance motor (SRM) is recently emerging as a cost-effective but mechanically and thermally robust motor for vehicle propulsion. However, the conventional driving method of the SRM causes a large input current and torque ripples, both of which are scarcely acceptable for vehicle application. Recently, a promising driving method has been proposed that tunes the phase current to eliminate the input current and torque ripples simultaneously, although this method suffers from large copper loss when applied to the normal SRMs. To solve this problem, this article proposes simultaneous tuning of the rotor shape in combination with the recently proposed driving method, which includes only tuning of the phase current. Tuning of the rotor shape is targeted at minimizing the copper loss. Meanwhile, the stator structure is the same as the normal SRM design. The proposed approach was revealed to reduce the effective value of the phase current by 18% in simulation and by 23% in experiment compared with the recently proposed driving method, without increasing the input current and torque ripples. This result suggests the effectiveness of tuning both the rotor shape and the phase current for applying SRMs to vehicle propulsion. [ABSTRACT FROM AUTHOR]

This article proposes an improved analytical method for accurate evaluation of flux-linkage characteristics for a given switched reluctance machine (SRM). Initially, air-gap inductance is calculated using an approximated analytical method, which incorporates the effect of fringing fluxes. Then, precepts of a conventional method are used to compute these characteristics under saturation, with a proposed new analytical model for nonuniform flux distribution in stator and rotor poles. Finally, for error quantification, these characteristics are benchmarked against those from a standard finite element analysis (FEA) based software. Both mean and standard deviation of the estimation errors are presented to quantify estimation accuracy. To establish its general validity, these characteristics are evaluated using the proposed method for six SRMs of different geometries and compared with those obtained from FEA. For further benchmarking, speed-torque characteristics obtained from the proposed method and FEA are presented and compared. Finally, both flux-linkage and torque-speed data are experimentally obtained from a 5 kW, 270 V, 12 000 r/min, 6/4 SRM and presented for validating the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

This article aims to propose a new hybrid reluctance machine equipped with relieving-dc-saturation (RDCS) ability for electric vehicle in-wheel drive. The proposed machine uses integrated ac and dc current excitation to eliminate extra dc field coils for the efficient torque generation. Besides, considering the inherent dc saturation in stator core caused by dc current excitation, slot PMs are artificially introduced to provide RDCS effect and thus boost torque density. Moreover, with a modular magnetic field configuration, the proposed topology exhibits excellent fault-tolerant potential at both open-circuit and short-circuit condition, making it suitable for safety-critical in-wheel vehicle propulsion. In this article, the machine configuration and operation principle are introduced, with emphasis on its RDCS effect and corresponding design consideration. Further, performance of this new topology is evaluated by both finite element analysis and prototype experiments. It is revealed that, with this RDCS ability, torque density of the proposed machine can be enhanced by about 25% under relatively high current density. [ABSTRACT FROM AUTHOR]

In this article, an universal sensorless starting scheme considering magnetic saturation effects is proposed to control the switched reluctance motor (SRM) drives. In this approach, the full-cycle unsaturated inductance can be reconstructed by converting the saturated incremental inductance into the unsaturated inductance with a simple mathematical model in the conduction region. Based on the reconstructed three-phase full-cycle unsaturated inductance, the inductance vector coordinate transformation method and the linear region inductance model based method can be applied for estimating the rotor position even under high load starting case. To verify the validity of the proposed methods, experiments have been implemented in a 1-kW three-phase 12/8 structure SRM prototype. The experimental results verify that the unsaturated inductance reconstruction scheme can transfer the nonlinear magnetic saturation problem into an unsaturation problem, and thus the rotor position estimation at the sensorless starting state can be simplified. The method can realize the initial position estimation and reliable sensorless starting control even under load conditions with only very simple initial inductance data acquisition, position partition logics design, and mathematic modeling. In addition, as the back-electromotive force is eliminated indirectly in the inductance calculation process, the adaptable speed range can also be extended. [ABSTRACT FROM AUTHOR]

This article presents the simultaneous magnetic and structural topology optimization of a transverse laminated synchronous reluctance machine rotor using a solid isotropic with material penalization (SIMP)-based approach with the globally convergent method of moving asymptotes (GCMMA) optimization algorithm. Magneto-structural single and multi-objective optimization formulations are presented. The single objective formulation maximizes the average torque subject to constraints on torque ripple, Von Mises stress, and compliance. The multiobjective formulation simultaneously maximizes average torque and minimizes compliance subject to constraints on torque ripple and Von Mises stress. In both optimization formulations, the electrical steel densities in the rotor mesh elements are the control variables. Including stress and compliance in the optimization formulation ensures a structurally feasible design. The design-dependent centripetal force contributed by each element in the rotor mesh is considered dependent on its density and mass. An intermediate density material issue is observed where the density of the material in a mesh element does not converge fully to air or electrical steel. This issue is addressed through the use of a thresholding mass function which forces the convergence of the mass but not the density. The two optimization formulations are compared for rotors operating at 4000 and 12 000 r/min. An initial magnetic only topology optimization is used to seed the magneto-structural topology optimization to decrease the computational time. The impact of the magnetic only seed and rotor mesh density on the optimization outcomes is also examined. [ABSTRACT FROM AUTHOR]

Relatively high torque ripple limits the further development of the switched reluctance machine, and the application of the ripple suppression method will reduce the efficiency of the system. To simultaneously improve the efficiency and torque ripple of the switched reluctance machine, a new commutation and online optimization strategy is proposed. According to the torque per ampere characteristics of the machine, two rotor position angles are defined, which are the boundaries for the high and low torque per ampere operation modes of the two adjacent phases, respectively, and for different operating modes, specific torque hysteresis control schemes are performed. Furthermore, an objective function is constructed with the efficiency and torque ripple coefficient, and during the operation of the machine, the defined boundary angles are online optimized by the genetic algorithm to maximize the value of the objective function. The effectiveness of the method is verified by detailed simulation and experiment under different operating conditions. [ABSTRACT FROM AUTHOR]

This article presents a general projection vector framework for the analysis of flux and position observers applied to sensorless control of synchronous reluctance (SyR) machines, with emphasis to parametric errors sensitivity. The stator resistance immunity property of Adaptive Projection vector for Position error estimation (APP) technique is demonstrated in maximum torque per ampere (MTPA) conditions. Out of MTPA, additional resistance adaption is devised for accurate estimation of stator flux and torque. Alternatively, inductance adaptation might be preferred to resistance's, when dealing with inaccurate motor flux-maps. Inductance adaptation is shown to decrease the steady-state position error. All the proposed APP observers with adaptation techniques are subjected to stability analysis. The merit and the feasibility of the proposed scheme are experimentally demonstrated on a 1.1-kW SyR machine test bench. [ABSTRACT FROM AUTHOR]

Inflating costs and emerging applications are spawning interests toward smaller and faster electric drives. The challenges of miniaturization make magnetic bearings more appealing, as they provide intrinsic high-speed capability and need virtually zero-maintenance. These advantages come at the cost of more sensors, which require a seamless integration especially at small geometrical scale. In the magnetic levitation domain, slice drives are particularly interesting, given their stabilizing passive characteristics that simplify the control of levitation and render the system simpler. These drives are already suitable for compressor applications, where control of all degrees of freedom is not necessary. In this article, the design process for a bearingless disc drive with a high degree of system integration is proposed. Two motor topologies, namely slotted and slotless drives, are rated by their passive stability, active properties, and power losses. Two sensor systems, fundamental for magnetic bearing commissioning, are proposed. They are simple to industrialize and offer a low footprint, thus not interfering with the drive design process. Ultimately, an optimization example is presented. For the presented scenario, drives with intermediate rotor size are the optimal contenders. Specifically among them, the slotless variant proves the best, given lower electrical losses and lighter mass compared to the slotted variant. However, the slotted becomes interesting if a stiffer magnetic bearing is needed. [ABSTRACT FROM AUTHOR]

This article deals with the design of high-speed synchronous reluctance motors for electric vehicle applications. The need to enhance the power density and to lower the cost leads to research on high-speed motors with a reduced amount of rare earth. Pure synchronous reluctance motors potentially operate at high speed and exhibit a cost-effective rotor compared to permanent magnets and induction motors. Nevertheless, they present reduced performances in deep flux weakening operations, in particular when the so-called radial ribs are introduced to increase the mechanical robustness of the rotor. In this article, the introduction of the radial ribs and the related design challenges are investigated and discussed. The adoption of the topology optimization tool that is able to optimize the amount, the positioning, and the sizing of suitable structural ribs is presented. A design flow integrating the topology optimization is presented. The approach leads to an original positioning of the radial ribs able to preserve the performance of the motor at high operating speed enhancing the mechanical integrity of the rotor. [ABSTRACT FROM AUTHOR]

The second harmonic current injection method is recently developed to enhance the torque density of variable flux reluctance machines (VFRMs). This article investigates the feasibility and effectiveness of the second harmonic current injection method in VFRMs with different stator/rotor pole combinations. By using magnetic gearing effect, it is found that the second harmonic injection method can only be applied to the 6j/(6i ± 2)j (i, j = 0, 1, 2…) stator/rotor pole VFRMs for the torque density enhancement. For the other stator/rotor pole combinations, the second harmonic current has no contribution in average torque production but only leads to excessive torque ripple. Further, by using global optimization method and finite element analysis, 6/8 stator/rotor pole combination is proved to be the optimal stator/rotor pole combination for 6-stator-slots VFRMs with the second harmonic current injection method, being able to exceed the maximal torque density of conventional VFRMs by 12% at a fixed copper loss. [ABSTRACT FROM AUTHOR]

Permanent magnet assisted synchronous reluctance (PM-SyR) motors often present relevant magnetic saturation, especially if overload capability is exploited. The knowledge of current-to-flux relationship is mandatory for proper motor control, and it becomes even more critical in the case of sensorless applications. Reliable standstill self-commissioning tests have been recently developed for synchronous reluctance (SyR) motors without producing rotor movement. This procedure can be extended to PM-SyR motors, but being at standstill, it does not retrieve the flux contribution related to the permanent magnets (PMs). This article integrates the identification of the flux characteristics including a novel test for estimating the PM flux linkage, obtaining the complete magnetic characteristic of the PM-SyR motor. The identification session is performed at standstill and without a position transducer, independently of the mechanical load being connected or not. Such conditions are considered the most demanding for self-commissioning tests. The machine is first excited with a proper sequence of bipolar high voltage pulses to determine its current-dependent flux components. Then, the estimate of PM flux linkage is retrieved at standstill by evaluating the local saliency along the negative q-axis. The proposed method is supported by detailed finite element analysis and experimentally verified on two PM-SyR motor prototypes, confirming the accuracy of the PM flux linkage estimate. [ABSTRACT FROM AUTHOR]

The direct torque control (DTC) and direct force control (DFC) method were introduced to reduce the torque and levitation force ripple in single-winding bearingless switched reluctance motors (SWBSRMs). However, it still has some disadvantages. Firstly, the flux-linkage control is not suitable for the DTC method in SWBSRMs. On the one hand, it can increase the torque ripple. On the other hand, the RMS current can be increased and then the torque-ampere ratio is decreased. Secondly, the vectors selection is also unreasonable, which can increase the torque ripple further. In order to solve these problems, an improved control method based on DTC and DFC method for SWBSRMs is proposed in this paper, which can obtain high torque-ampere ratio and low torque ripple simultaneously. In the proposed method, the flux-linkage loop control is not needed and the space voltage vector table is improved. The experimental results show that the torque ripple is reduced by 66.7%, the torque-ampere ratio is increased by 200% and the switching times in one electrical period are reduced by 47.3%. [ABSTRACT FROM AUTHOR]

This paper presents a new design of dual-pole (4-pole and 8-pole) Line Start Synchronous Motor (LSSM) with consequent magnetic pole structure. The proposed structure reduces the Permanent Magnet (PM) volume in the rotor core by 67 percent with respect to the reference dual-pole machine. Given the direct impact of the PM magnetic field on producing negative torque components such as braking torque and pulsating torque, lower PM volume can potentially limit the production of such negative torques. Therefore, in addition to cost saving benefits, the proposed structure contributes to a smooth start-up process. Meanwhile, different geometrical structures of PMs and flux barriers are discussed, their impacts on the overall motor performance are highlighted, and general design guidelines are provided. In particular, six different rotor structures with different PM arrangement and/or flux barrier arc angle are analyzed in Finite Element (FE) and their steady-state and transient performance metrics are compared. Finally, the best motor candidate is selected for further analyses, and prototyping. [ABSTRACT FROM AUTHOR]

In conventional 12/8 bearingless switched reluctance motors (BSRMs), the generation and control of torque and levitation forces are always coupled and interacted, which increases the complexity of the current control algorithm. In this paper, a novel BSRM with 12 stator poles and 4 rotor poles is proposed to simplify the control of torque and levitation, which has wide flat inductance region. Through allocating the generation of torque and levitation forces to different inductance regions of each phase, the levitation control can be similar as that of magnetic bearings, and the torque control can adopt the methods of conventional switched reluctance motors, e.g. current chopping control and angle position control. Accordingly, the current control algorithm of proposed BSRM becomes very easy and flexible. Extensive experiments were completed to verify the demonstrated performance of proposed motor. [ABSTRACT FROM AUTHOR]

In this paper, a dual-consequent-pole transverse flux motor and its electromagnetic design method are proposed. Both the stator and rotor of the proposed motor are designed to own the consequent-pole configurations. The unique motor structure improves the space utilization and the torque density. Firstly, the detailed structure and principle are introduced, and the development of the torque density of the proposed motor is discussed. Secondly, the electromagnetic design method's theory, considerations and flow process are listed. Then, the selections of some main structure parameters are proposed (e.g., pole-pitch, thickness of PMs and pole-arc coefficients of PMs). The electromagnetic performances of the proposed motor are compared with the existed transverse flux machines. At last, a prototype is manufactured and some primary experiments are done to verify and evaluate the proposed motor topology. [ABSTRACT FROM AUTHOR]

In this article, we present a new configuration of bearingless slice motor that levitates and rotates a ring-shaped solid steel reluctance rotor. The rotor is 50 mm in diameter and has salient features on the outer surface. Symmetric sets of Halbach magnet arrays, mounted on the tips of stator teeth, establish a homopolar bias flux around the rotor. The bias flux passively stabilizes the rotor in the out-of-plane tilts and axial translation, whereas the rotor's radial translations are actively stabilized by feedback control. The rotor saliencies spatially modulate the air-gap bias flux such that the resulting torque-current relationship is similar to that of permanent-magnet synchronous machines. We have designed, built, and tested a prototype bearingless motor and control system. The prototype system achieves a torque constant of 14.9 mNm/A, maximum speed of 5500 r/min, and suspension bandwidth of 84 Hz with a phase margin of 11.3 $^{\circ }$. The rated torque and speed are 26.8 mNm and 3486 r/min, respectively, and the axial and tilting passive stiffnesses are 15.3 N/mm and 34.4 mNm/ $^{\circ }$ , respectively. [ABSTRACT FROM AUTHOR]

This article develops a modified dynamic reluctance mesh (DRM) method that can be utilized to calculate and analyze the magnetic field of the iron-cored tiered-type permanent magnet spherical motor (T-PMSpM) effectively and efficiently, with the multi-degree-of-freedom (multi-DOF) movements taken into account. According to the structural characteristic of the iron-cored T-PMSpM, the tilting function part, including the tilting stator and rotor, is equivalent to a dynamic lumped-parameter magnetic network model. Besides, the magnetic saturation phenomenon of the iron materials is also considered. The DRM results of magnetic field distribution, flux linkage and back electromotive force (EMF) show a good agreement with the three-dimensional finite-element method results. For further verification, a prototype motor of the iron-cored T-PMSpM has been manufactured. The back EMF curves with different rotor tilting positions are measured by experiments and compared with the calculated results. [ABSTRACT FROM AUTHOR]

Hybrid stepper motors, which convert the input pulse train into rotating angle increments by using an open-loop control strategy, are widely used in industrial applications. The bearing is a key and vulnerable component in stepper motors, and the bearing faults affect the positioning accuracy and output torque of motors. Order analysis is an effective method in bearing fault diagnosis under varying speed conditions. The rotating angle curve is necessary for order analysis, but angle or speed sensors are not installed on hybrid stepper motors. In this article, a method of estimating the rotating angle from motor current is proposed and applied to bearing fault diagnosis. First, a variational nonlinear chirp mode decomposition method is introduced to decompose the current signal and extract a dominant mode that has a strong correlation with motor rotation. Second, the rotating angle is calculated, and the synchronous vibration signal is resampled using the rotating angle curve. Finally, the bearing fault type is identified from the envelope order spectrum of the resampled signal. The proposed method can accurately diagnose bearing faults and has potential applications in condition monitoring of stepper motors. [ABSTRACT FROM AUTHOR]

Switched reluctance machines (SRMs) have been studied by many researchers as an alternative to the other types of electrical machines for use in electric and hybrid vehicle applications. SRMs are fault tolerant and have wide speed operating range. However, they suffer from several disadvantages, including high vibration, acoustic noise, and torque ripple. In this article, the placement of rectangular windows in both the rotor and stator poles is proposed to reduce the vibration and acoustic noise of SRMs. An iterative optimization algorithm in a wide speed range of operation using finite-element analysis (FEA) tools provides the best position and dimension of window design parameters. Multiphysics FEA is also performed to predict the vibration and acoustic noise of the optimized design. The results of this study present that placing windows in both the stator and rotor of the SRMs can significantly reduce the acoustic noise compared with the baseline SRMs. Based on the simulation results, the optimum design has been constructed as a prototype and tested in a wide speed operating condition. The simulation and experimental test validation results prove the effectiveness of the proposed design in mitigating the acoustic noise and vibration. [ABSTRACT FROM AUTHOR]

The article presents a general framework valid for the high-frequency excitation-based position observer for low-speed sensorless control of synchronous reluctance machines. A finite-control-set model-predictive-control technique is proposed accordingly, exploiting the switching current ripple for the position estimation. The position error due to cross saturation is inherently accounted for. The proposed scheme is integrated with an adaptive projection vector for position error estimation for high speeds region through a simple fusion structure for a smooth transition. The performance of the proposed technique is validated on a 1.1-kW synchronous reluctance motor test bench. [ABSTRACT FROM AUTHOR]

This article deals with the design of a normal saliency interior permanent magnet (PM) motor, also referred as flux-intensifying PM motor. A multibarrier rotor geometry is adopted and studied through an analytical model to obtain an almost sinusoidal airgap flux density waveform, so as to improve the performance and reduce the torque ripple. The developed analytical model is generic and applicable for any number of rotor flux barriers and for any number of poles. The motor performance improvement has been evaluated by finite-element analysis. Experimental validation has been carried out on a motor prototype. [ABSTRACT FROM AUTHOR]

Iron saturation affects the low-speed and standstill rotor position estimation of synchronous motors based on high frequency voltage injection, leading to an estimation error. In the case of a heavily saturated machine, the estimation algorithm could even fail, due to the absence of convergence points, making the sensorless drive impractical. This article examines in depth the mentioned problem of convergence in salient rotor machines; a synchronous reluctance motor is assumed as case study since this kind of machine is considerably affected by iron saturation. At first, the article models and describes in detail the high frequency voltage injection estimation mechanism. Then it analyzes the convergence conditions and investigates the dependence of the estimation convergence range on the amplitude and phase of the reference current vector of the drive. Moreover, it proposes different methods to enhance the estimation convergence range, improving the accuracy as well. A comparison between the different approaches is given as well as hints for their design. At last, the impact of airgap space harmonics is pointed out. The results are validated by simulations and experimental tests. [ABSTRACT FROM AUTHOR]

A systematic approach based on a novel space-shifted three-layer winding (SSTLW) to eliminate both the sub- and superharmonics of fractional slot concentrated winding ac machines is presented. In this proposed three-layer fractional slot winding, the number of turns in one layer and the relative positions of other two layers are optimized to cancel subharmonics. The cancellation of superharmonics is achieved through series connection of two SSTLWs through effective doubling of the number of slots. The cancellation of the dominant sub- and superharmonics using this approach leads to reducing the total harmonic distortion, torque ripple, PM eddy current loss, and rotor core loss, while simultaneously improving power factor and saliency ratio. The proposed design methodology and ensuring improvements have been validated through finite element analysis for the widely used 12-slot/10-pole and 18-slot/14-pole permanent magnet synchronous machine (PMSM) configurations. A prototype three-layer winding is built for a 10-pole PMSM to validate the simulation results experimentally. [ABSTRACT FROM AUTHOR]

To meet different loading requirements in the metal industry, special attention must be paid to the operational performances and start-up characteristics of those electric motors implemented for desired driven applications. However, because of the global warming and energy conservation concerns, the enforced operational regulations have increased the complexity of those commonly applied induction motors for supplying the desired equipment driven forces. By adopting the same stator, the synchronous reluctance motor (SynRM) can be achieved with properly redesigned rotor structure of an induction motor. Due to its robust structure and lack of secondary copper loss, it is very competitive for the related hoist, punch, roller, and pump applications. Furthermore, by inserting adequate ferrite permanent magnets and conductors into the rotor barriers, composition designs of the direct-on-line SynRMs (DOL_SynRMs) will also be proposed. The operational characteristics of the DOL_SynRMs for fulfilling different specifications will all be thoroughly investigated and confirmed by experimental measurements. The DOL_SynRM structures that can provide potential alternatives for related high-efficiency metal industry-driven applications can thus be validated. [ABSTRACT FROM AUTHOR]

This article proposes a new five-phase flux-intensifying fault-tolerant interior-permanent-magnet (FIFT-IPM) motor to realize high fault tolerance and sensroless operating capacity of the motor drive system for electric vehicles (EVs). By employing the new concept of flux intensifying, the proposed motor owns the outstanding characteristic of Ld > Lq, which can contribute the sensorless operation significantly. By integrating the special design of the stator tooth, using the masterly permanent-magnet (PM) placement and increasing the length of air gap in the q-axis, the high fault tolerance and high reliability can be obtained, which is essential for EV applications. The static performances of the proposed motor are investigated by using finite-element analysis. And the corresponding sensorless operation experiments are implemented based on the prototyped motor. Both theoretical analysis and the experimental results verify the validity of the proposed five-phase FIFT- IPM motor design. [ABSTRACT FROM AUTHOR]

This article proposes a new fault-tolerant permanent magnet (FTPM) machine with the improved salient ratio and reluctance torque ratio. The key of the proposed machine is the new slot–pole combination (20-slot/14-pole), which breaks the traditional rule which stipulates that the difference between slot number and pole number in FTPM machines is equal to 2. After the selection of slot–pole combination, the influence of the ratio of armature diameter to length and the injected current on salient ratio and reluctance torque ratio is evaluated, indicating that the relationship between the salient ratio and the reluctance torque ratio is contradictory in the FTPM machine. Therefore, the multiobjective method is employed to obtain optimal rotor parameters. In order to confirm the superiority and the uniqueness of the proposed FTPM machine, the comparison between the proposed FTPM machine and the two traditional FTPM machines (20-slot/18-pole) is analyzed. From the finite-element method and experimental results, it clearly depicts that the designed 20-slot/14-pole FTPM machine exhibits good fault-tolerant capacity, the improved salient ratio and reluctance torque ratio. [ABSTRACT FROM AUTHOR]

This paper makes the case that Switched Reluctance Motor (SRM) is an exceptionally attractive technology to respond to the increasing demand in propulsion applications for high-efficiency, high-performance, and low-cost motors with a more secure supply chain. The paper also presents methods to effectively reduce torque ripple and acoustic noise, which have been the major issues impeding the widespread use of SRMs. Finally, SRM designs for two propulsion motors, one for an e-bike and the other for a hybrid electric vehicle application, are presented which have been proposed to replace permanent magnet machines. [ABSTRACT FROM AUTHOR]

In this article, a dual-pulse mode control of a high-speed doubly salient electromagnetic machine (DSEM) for efficiency improvement over a wide speed range is investigated and implemented. The dual-pulse mode control method and operation principle are introduced. The influence of excitation angles and field current on the operation performance is analyzed by finite-element method based on the back electromotive force (EMF) and inductance characteristics. The loss distribution for various speed and load torque requirement is attained, and the control parameters are optimized. The excitation angle can reduce the back EMF at high speed through transformer EMF and flux-weakening armature reaction. A prototype of 12/8-pole DSEM drive system is developed and dual-pulse mode control in high-speed operation under low dc-link voltage is implemented. Both the simulated and measured results show that the torque capacity of the DSEM is improved and the loss is reduced over a wide speed range. [ABSTRACT FROM AUTHOR]

Amorphous magnetic materials (AMMs) have been commercially available for decades. However, their application to electrical machines still lacks of breakthrough progress. This article proposes to use the AMM for a high-speed interior permanent-magnet rotor to avoid sleeves. In this application, advantages of the high mechanical strength, the low core losses, and the relatively low-saturation flux density of the AMM are fully taken. In order to ensure the success of the proposed application, three important aspects: slotting, electromagnetic properties, and mechanical strength of the AMM are experimentally studied. Since the electromagnetic properties of the AMM core are sensitive to the mechanical process, stress, and temperature, the AMM cores are tested and the tested data are used for the motor design. Finally, a prototype is built and tested. [ABSTRACT FROM AUTHOR]

In order to increase structure compactness, critical rotor speed, and output torque of existing 12/12 bearingless switched reluctance motor (BSRM) with axial-biased permanent magnet, an improved modular permanent magnet BSRM is comprehensively investigated. First, basic structure and operation principle for torque and suspending force are briefly introduced. Second, magnetic design, including torque and suspending force, is taken into account. In addition, basic size estimation, self-starting capability, maximum suspending force, and selection of secondary air-gap are comprehensively considered in design. Third, several characteristics, such as torque, suspending force, etc., are deeply analyzed. Finally, a prototype motor is manufactured based on the above-mentioned analysis and design method. And the implemented experiment results show that the improved structure has good performance. [ABSTRACT FROM AUTHOR]

This article analyzes an engineering problem of adjusting the rated current of a synchronous reluctance motor to match the rated current of a commercially available inverter. This situation may occur when a synchronous reluctance motor is optimally designed for maximum torque per ampere (MTPA) operation using standard IEC stator frames for induction motors. When the motor has a maximized saliency ratio along with MTPA control at rated speed and available inverter voltage, it often happens that rated current of the motor exceeds the rated current of a commercially available inverter. This article shows that the motor current can be reduced and power factor increased by choosing different number of turns per coil and even changing the stack length. In other words, rewinding and axial scaling of the motor is performed in order to retain the same rated voltage and shaft power and hence to operate with better power factor which means lower current and lower kVA requirement. This comes with a certain increase in slot current density and therefore reduction of motor efficiency. All the design tradeoffs, which emerge in this situation and their effects on the motor performance are explained using a linear model of the motor based on a phasor diagram with constant inductances. The predictions of the simple analytical model were confirmed by utilizing flux linkage versus current maps obtained from nonlinear finite element analysis and afterward by conducting measurements on two identical motors wound with different number of turns per coil. [ABSTRACT FROM AUTHOR]

Position sensorless control of synchronous reluctance machines is not easy due to nonlinear correlations caused by extensive magnetic saturation. This article investigates stability of a conventional saliency-based method and, for the first time, shows that the method becomes unstable at high torque with high magnetic saturation not due to cross-coupling effect itself but due to expansion of the cross-coupling effect through feedback of the estimated position. This instability occurs even when neither disappearance of the saliency nor reversal of the estimated d- and q- axes arises. A novel method to overcome this instability is proposed, which utilizes magnetic saturation depending on current phase angles. The proposed method was verified by simulations and experiment using a prototype machine. The results demonstrated that the proposed method achieved stable sensorless operation at the maximum torque, and thus, surpassed the conventional saliency-based method, the feasible torque of which was limited to 60% of the maximum for the prototype machine. [ABSTRACT FROM AUTHOR]

Modeling and accurate estimation of mutual flux in switched reluctance motors are complex due to interphase flux interactions, magnetic saturation, and harmonics. The mutual flux contributes significantly toward torque production of mutually coupled switched reluctance motors (MCSRMs); therefore, their accurate modeling directly influences the control design. In this article, a net-flux-based machine model is proposed to model MCSRMs. The model utilizes dual-phase excitation and multiphase excitation methods to generate the flux lookup tables from the finite-element model of the MCSRM. The modeling process is simple, as it does not require the segregation of the self- and mutual flux components, and machine performance can be predicted accurately using the net flux. The proposed modeling method is validated by implementing it for a fully pitched and concentrated-wound MCSRM and evaluating accuracy against the finite-element method. Details of the developed model are presented along with its comparison with existing methods. A prototype of a fully pitched MCSRM has been built, and the model is validated experimentally. Results show that the proposed model has excellent accuracy even under saturated operating conditions. [ABSTRACT FROM AUTHOR]

This article presents a review in three parts on the current traction motor topologies available in the railway market. In the first part, essential aspects of the electromagnetic design of railway traction motors, e.g., motor sizing and rotor configurations, are discussed. Different topologies are compared considering the wide range of applications. The pros and cons of each topology in specific applications are highlighted based on the corresponding performance requirements. In the second part, different cooling configurations of traction motors common in railway are reviewed, focusing on the solutions based on air cooling. The third part presents a review of the available insulation systems for traction motors. Two primary insulation systems used in traction applications with thermal classes of H and N are discussed. The focus in this article is placed on the main applications in railway including light rail vehicles, metros, electric multiple units, high-speed trains, and locomotives. Additionally, trends in traction motors development in the coming years are reported separately for electromagnetic, cooling, and insulation designs. [ABSTRACT FROM AUTHOR]

This paper presents a method to control the speed of doubly fed induction motors. The motivation lies in the possible use of such motors for hybrid electric propulsion. The stator of the motor is assumed to be supplied by three-phase voltages with frequency and magnitude that may vary. The rotor is supplied by a bidirectional converter. Two versions of the algorithm are presented. The first version does not rely on inner current loops, but instead commands directly the voltages applied to the rotor. These voltages are computed using an open-loop controller for torque and for stator reactive power, which is augmented to follow a speed reference profile. The second version uses stator and rotor current measurements to ensure tracking and limiting of the rotor currents. All the parameters of the control systems can be computed based on estimates of the machine parameters together with a desired time constant of the speed response. The alignment of an incremental encoder is integrated in the initialization of the algorithm. Practical implementation and testing are performed easily and rapidly. Experiments performed on a small-scale laboratory testbed show very good tracking performance of a speed profile in tests involving one motor, as well as two motors on a single three-phase supply. Improved current limiting is observed with the version incorporating current feedback. [ABSTRACT FROM AUTHOR]

The rotor structure of synchronous reluctance machines (SynRel) is conventionally retained mechanically by iron ribs. In this paper, a novel structure for high-speed synchronous reluctance rotor is presented. The novelty of this paper is the proof of a concept of SynRel machine without iron ribs. Structurally, the rotor iron lamination segments are embedded in an adhesive resin material with high temperature resistance and mechanical strength. Three four-pole SynRel machines have been designed with the target of improving motor torque, and compared for different ribs configuration. It has been shown that the proposed motor performs enhanced torque, power factor, and efficiency with respect to conventional SynRel with iron ribs. An extensive sensitivity analysis of the ribless rotor geometry is carried out, followed by both mechanical analysis and experimental over speed test to guarantee its robustness above the operating speed range. The manufacturing procedure of this novel rotor is introduced. Finally, the experimental results on both SynRel prototypes are presented, showing the increase in torque, power factor, and efficiency of the proposed solution. This paper is a first step toward the definition of a viable and novel solution of SynRel machines with improved performance. [ABSTRACT FROM AUTHOR]

This paper presents a novel position sensorless control for 6/4 switched reluctance motors (SRMs) using only one-phase current sensor in medium and high speed. In order to eliminate phase voltage sensors, a virtual phase voltage is established to replace the real-time phase voltage in the whole conduction cycle, so as to calculate the phase flux linkage which is called virtual flux linkage. A nonlinear model is utilized to estimate the reference flux linkage-curve of any rotor position. With only one-phase current sensor, the determination of turn off angle position and phase commutation position is achieved by the comparison of reference flux linkage and virtual flux linkage. The speed estimation is performed by two reference flux linkage-current curves at particular rotor positions. Based on the obtained turn off pulse of the present phase and the turn on pulse of next phase, the remaining trigger pulse signals of three phases are derived from a delay-time strategy. The proposed scheme requires only one-phase current sensor, without any pulse injection or complicated decoupling algorithm, achieving a simple and cost-effective drive. Simulations and experiments are carried out on a 6/4-pole prototype SRM drive system to verify the correctness and effectiveness of the proposed sensorless control scheme. [ABSTRACT FROM AUTHOR]

High speed machines are gaining popularity in more and more applications. Besides permanent magnet (PM) machines, switched reluctance machines (SRMs) are very competitive candidates for high-speed applications in high-temperature environments due to their single material rotor without PMs. However, the conventional rotor geometries of SRMs are not suitable for the ultra-high speed applications. In this article, a novel high-strength, high-torque-density, high-efficiency rotor design for the ultra-high speed SRMs is proposed. First, a three-dimensional finite-element analysis is conducted to calculate the von-Mises stress distribution of the proposed rotor and shaft. Then, in order to improve the bonding and robustness of the design, proper high-strength adhesives are used and modeled based on the cohesive zone model. A parametric study is conducted to find the optimal length of the rotor stack. A thermal stress case study is also conducted. Finally, several prototypes are built to validate the manufacturing feasibility of the proposed design. [ABSTRACT FROM AUTHOR]

This article is a contribution to answer the following question: Is it possible to design a permanent magnet machine with the performance expected from rare-earth magnets but at a lower cost? Performance being understood as torque, size, efficiency, demagnetization, and temperature rise together. The question is addressed with a systematic exploration of different interior permanent magnet machine topologies mixing rare-earth and ferrite permanent magnets. The study starts from a production baseline, the Prius 2010 traction motor, with interior magnets placed in a single V pattern. It investigates various rotor designs, most specifically, single V and double V patterns as well as spoke configurations. The stator cross-section design and winding selection are fixed, providing a solid comparison basis from the point of view of machine cooling. For each rotor design, torque potential and machine material cost are assessed, the latter expressed as torque per dollar. A promising configuration was found based on a spoke pattern for which further modeling was performed to assess efficiency as well as mechanical strength and resistance to short circuits and to demagnetization. It reduces the rare-earth magnet volume by over 60%. [ABSTRACT FROM AUTHOR]

The rotor conductor bars of the line-start synchronous reluctance motor (LS-SynRM) make the motor have self-starting capability. The distribution of the rotor conductor bars not only has a great impact on the starting capability, but also affects the steady-state performance of the LS-SynRM. The steady-state performance of the LS-SynRM mainly depends on the inductance parameters. And the distribution of the rotor conductor bars directly affects the variation of the inductance parameters, especially the d-axis inductance. Based on the steady-state characteristics of LS-SynRM, an evaluation method based on finite element analysis (FEA) is proposed to determine whether the rotor conductor bars of LS-SynRM is reasonable. First, the d-axis inductance reference model without rotor conductor bars is established, the target of optimize is to reduce the weakening effect of rotor conductor bars on the d-axis inductance, and the optimal distribution structure of rotor conductor bars is determined. The optimization results show that the d-axis inductance of the determined rotor conductor bars structure in this article reaches 96.2% of the reference inductance and the distribution of the rotor bars achieves better results. It is verified that the improved LS-SynRM has better efficiency, starting capability, and maximum torque than the initial LS-SynRM by FEA and prototype test. At the same time, comparing with the performance of the three-phase squirrel cage induction motor for compressor, it is proved that the improved LS-SynRM has higher efficiency and a good application prospect. [ABSTRACT FROM AUTHOR]

It is an effective approach to estimate rotor position of doubly salient electromagnetic machine (DSEM) from self-inductances, which changes with rotor position. To overcome the restrictions of low estimation accuracy as well as the inevitable commutation lag in the conventional sensorless startup method, this paper proposes a novel rotor angular position estimating technique for the DSEM sensorless startup. It starts with injecting three test pulses A + C- (phase A is connected to the positive rail of dc bus, and phase C is connected to the ground rail), B + A- and C + B- on armature windings, so two-phase series self-inductances can be identified according to the resultant currents. Then, the estimating expression of the DSEM rotor angular position is further obtained based on the geometrical relation in the rectangle composed of self-inductances, and the inevitable commutation lag in startup process is likely to be eliminated with the estimated rotor angular position. Moreover, the error of rotor angular position introduced by the nonideal linearity of self-inductances are analyzed in detail, and the boundaries of neighboring sectors are distinguished from normal sectors to compensate the estimation error of rotor angular position. Finally, to enhance the output torque performance during the DSEM startup process, a novel selection method for test pulses concerning rotor sector is developed. Compared to the conventional method, a quicker and superior startup performance is achieved since no negative torque is generated by the test pulses. The experiments on a 12/8-pole DSEM validate the correctness and feasibility of the proposed sensorless control methods. [ABSTRACT FROM AUTHOR]

The synchronous reluctance (SyR) machine is an attractive substitute of induction motors and synchronous permanent magnet motors, owing to its high efficiency and low cost of manufacturing. Yet, its design cannot be considered a mature topic, especially for what concerns the rotor geometry. Design equations are proposed for SyR machines by different authors, representing a good starting point and a useful guideline for designers, but they are far from giving accurate results. Conversely, the design procedures based on finite-element analysis (FEA) tend to rely on the brute force of optimization algorithms rather than on the designer's insight. In this article, a comprehensive design procedure is proposed, where design equations are complemented by the use of the iron saturation curve and the new fast FEA approach named FEAfix. This corrects the equations results via few static FEA simulations per design plane, i.e., per family of machines, rather than by FEA simulating the single machine under design. The general conclusion is drawn that the considered analytical model alone tends to overestimate torque by as much as 40% (average on the design plane). Upon augmenting equations with the saturation curve, the average overestimate drops in the vicinity of 10% error. Finally, the proposed FEAfix refinement guarantees 2% to 1% torque evaluation error, depending on the admitted computational time. High precision is, therefore, obtained while retaining the generality of the analytical approach. [ABSTRACT FROM AUTHOR]

This paper presents a scheme for rotor position estimation from standstill to nominal speed. The proposed scheme is particularly suited for surface mounted permanent magnet synchronous motors and for slotless permanent magnet synchronous motors with completely smooth cylindrical rotor, which cannot be operated with state-of-the-art sensorless methods seamlessly from standstill. At standstill and very low speed, the position is estimated by using signal injection. A systematic distortion in the position estimation that is due to asymmetries in the motor parameters is identified and compensated. The rotor polarity is identified by a special process based on the estimation of the back electromotive force (back EMF) induced by a minimal rotor motion. At high speed, the position is estimated by using a linear back EMF observer. Different observer gains are used at different speed ranges, so that the position estimate is reliable even at low speed. The combination of these two approaches enables sensorless motor control in the full speed range including standstill. Experiments demonstrate the accuracy of the proposed estimation scheme and its robustness under different thermal conditions. This paper is accompanied by two videos demonstrating sensorless operation. [ABSTRACT FROM AUTHOR]