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This article focusses on power quality issues related with the operation of a wind energy conversion system employing a doubly fed induction generator (DFIG), integrated with a solar photovoltaic array, under unbalanced, and distorted grid conditions. The multiple-order DFIG electromagnetic torque ripples and grid active power ripples, resulting from the unbalanced and distorted grid, can be mitigated, however, at the cost of highly unbalanced and distorted currents. This article provides a possible solution towards a tradeoff by developing a flexible ripple minimization technique based on a cross-feedback extended second order generalized integrator for harmonics sequence separation (CextSOGI-HSS). The CextSOGI-HSS based current compensation enables a controlled minimization of ripple as per the customizable flexibility quotient. Furthermore, the current compensation technique employs an improved recursive least squares (IRLS) adaptive filtering algorithm for processing DFIG stator currents and local load currents. The IRLS algorithm improves grid currents harmonics spectra by filtering-out higher order harmonics from DFIG stator currents and nonlinear load currents, meanwhile, the effects of any load or stator currents unbalance on grid currents are also mitigated. Test results from a developed laboratory prototype confirm the efficacy of the presented flexible ripple minimization control technique. [ABSTRACT FROM AUTHOR]

This article illustrates a method for sensorless control of a switched reluctance motor. The detection of the time instants for switching between the working phases is determined based on the evaluation of the switching frequency of the hysteresis current controllers for appropriately selected sensing phases. This enables a simple and cost efficient implementation. The method is compared with a pulse injection method in terms of efficiency and resolution. [ABSTRACT FROM AUTHOR]

This article proposes a model for obtaining the failure path current and torque waveforms in synchronous machines with saliency under interturn short circuits (ISC). The variations of the magnetomotive force (MMF) due to an ISC can lead to changes in the inductances, which lead to errors when modeling motors with ISC. A compact approach based on complex numbers is proposed to solve the dynamic ISC equation. The proposed method uses rotor reference frame variables and parameters as inputs. These rotor reference frame quantities are transformed to a stationary frame aligned with the faulted coil, thus extracting the real part of these quantities, allowing to solve the ISC dynamic equation quickly. Look-up tables are implemented to account for the MMF variations due to an ISC and saturation. The proposed model is validated with finite element analysis and experiments. [ABSTRACT FROM AUTHOR]

With high surrounding temperatures, winding resistance increases and thus lowers the operational efficiency of a motor. To meet the large application requirements and conform with the ever-increasing energy-efficiency regulations for pump equipment in the metals industry, consistent efforts have focused on producing single-phase motors that can deliver superior performance at a low cost. Because the steady-state rotational speed is synchronized and no driver circuit is required, a direct-on-line synchronous reluctance motor is a potentially viable alternative to the commonly adopted induction motors. Its inherently simple structure and comparably low operational speed necessitate a challenging structural design for accomplishing the high-efficiency objectives of pump applications. These challenges and their potential solutions are reported in detail. By employing a systematic design scheme and including thermal concerns of the performance, a competitive high-efficiency single-phase direct-on-line synchronous reluctance motor for pump applications in various metal industry equipment was offered. [ABSTRACT FROM AUTHOR]

This article proposes a nonlinear controller based on feedback linearization (FL) for synchronous reluctance motor (SynRM) drives which takes into consideration the magnetic saturation. The proposed nonlinear FL control based control technique has been developed starting from the theoretical definition of an original dynamic model of the SynRM taking into consideration both the self- and the cross-saturation effects. Such a control technique permits the dynamics of both the speed and axis flux loops to be maintained constant independently from the load and the saturation of the iron core in both constant flux and variable direct axis flux operating conditions. Finally, sensitivity of the performance of the proposed FL control versus the variation of the main motor parameters has been verified. The proposed technique has been tested experimentally on a suitably developed test setup. The proposed FL control has been further compared with the classic field-oriented control (FOC) in both constant flux and variable flux working conditions. [ABSTRACT FROM AUTHOR]

This article proposes a novel asymmetric interior permanent magnet (AIPM) rotor topology that has a mixed V-shape and spoke-type PM configuration, designated as a 1.5-layer PM structure, and asymmetric arrangement of V-shape PMs and asymmetric flux barriers. The AIPM rotor topology is employed for IPM synchronous machines to utilize the magnetic-field-shifting (MFS) effect for increasing average torque by reducing the current angle difference between peak PM and reluctance torque components. Three machines, i.e., the proposed 1.5-layer AIPM, a symmetrical 1.5-layer IPM-I, and a conventional V-shape benchmark IPM-II are designed and optimized using the same stator, rotor diameter, and total PM usage by global parametric optimization considering the mechanical stress. The effect of asymmetric features of the 1.5-layer AIPM rotor design, i.e., asymmetry of V-shape cavity as well as position and dimensions of flux barrier, on maximum torque and open-circuit air-gap field are investigated. The electromagnetic performances of three machines are compared. It confirms that the proposed AIPM machine has the highest maximum torque and the smallest cogging torque simultaneously. It is also revealed that the torque enhancement is achieved by both the 1.5-layer structure and MFS effect. Finally, a prototype of an AIPM machine is manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

This article compares the performance of an existing three-phase synchronous reluctance machine (SynRM) with an identical machine that is upgraded to a five-phase machine. Two different methods are possible to convert the existing three-phase machine to a five-phase one with minimum cost. In the first method, a five-phase SynRM (SynRM 1) is obtained by replacing the existing stator by another one that has an integer number of slots per pole, i.e., a multiple of five. In the second method, a five-phase SynRM (SynRM 2) is obtained by rewinding the existing stator with a special type of winding. This is because the slot number of the existing stators is not a multiple of five. The novelty of the article is that two five-phase SynRMs are compared with the original three phase reference machine in terms of torque and torque ripple, in healthy and fault conditions. At rated condition and optimal current angle, SynRM 1 performs better than SynRM 2 in terms of rated torque: SynRM 1 and 2 have 11.8% and 6.6% higher torque than the three-phase machine. But, SynRM 1 has 25% more torque ripple than the three-phase reference machine, while SynRM 2 has 17% lower torque ripple. At faulty case, SynRM 1 and 2 work at 74% and 79% of the healthy rated torque of the three-phase SynRM, while the three-phase SynRM works at only 43% with a very huge torque ripple. Finally, experimental measurements are obtained to validate the theoretical work. [ABSTRACT FROM AUTHOR]

This article proposes a novel asymmetric-magnetic-pole interior permanent magnet (AMP-IPM) machine, which is geometrically characterized by a combination of dual-layer reluctance and flat-type PM rotor structures. The design concept of “asymmetric-magnetic-pole” is introduced to achieve a magnet-axis-shifting effect, namely, the magnet d-axis is shifted to make PM and reluctance torque components approximately maximize at similar current angles. Consequently, the resultant torque can be further improved without increasing magnet usage. The machine topology is first introduced. The electromagnetic characteristics of the proposed AMP-IPM machine are then investigated and compared with those of the benchmark conventional IPM machine with symmetrical magnetic poles, with similar sizing and PM usage. Finally, an AMP-IPM machine prototype is manufactured and tested, which confirms the feasibility of the proposed AMP design for the torque performance improvement. [ABSTRACT FROM AUTHOR]

This article reports design and testing of silicon carbide) devices-based three-phase asymmetric H-bridge converter capable of switching at 50 kHz and intended to drive high-speed switched reluctance machine. Electromagnetic designs of a 7.5-kW, 30 000-r/min and a 20-kW, 50 000-r/min Switched reluctance machine are presented. The 30 000-r/min machine is fabricated and characterized. A machine model is obtained from the measured characteristics. Based on the machine model, as well as drive operating variables and device data-sheet parameters, two methods are proposed for evaluating the losses in the power devices. The first method relies on machine model to obtain machine current and converter duty ratio, and thereby estimate the device losses. A second simplified method provides closed-form expressions for device losses. The proposed analytical expressions relate the machine characteristics such as inductance and saturation current with converter losses. The estimated loss is further used to predict device junction temperature. The power converter and device ratings are chosen so that the converter is suitable for both machines. The capacitor selection and sizing are discussed. Further, the power converter architecture and other subsystems of the converter are described. Test results are presented for the asymmetric H-bridge converter at 800 V dc bus voltage, 50 A of load current, and 50 kHz of switching frequency. Thermal image is presented for validation of estimated heat-sink temperature. The predicted heat-sink temperature is found to agree well with the measured temperature. The power converter is used to operate the 30 000-r/min machine at various speeds. [ABSTRACT FROM AUTHOR]

A direct-on-line synchronous reluctance motor (DOLSynRM) with a rotor topology defined by the natural flux line curve approach is studied as an alternative to an induction motor (IM) using a 1.5 kW, 50 Hz synchronous reluctance motor as an example. If an IM stator is used, a direct squirrel cage rotor replacement by a synchronous reluctance rotor equipped with a damper winding might not guarantee a sufficient starting performance. To ensure the strong enough starting capability, the natural flux line curve approach was modified in the motor design. The proposed approach was applied in the optimization of the DOLSynRM using a genetic algorithm. The optimization results show a clear tendency in the rotor design when trying to achieve a reliable starting capability and to maximize the steady-state performance of the DOLSynRM. Both the stator design and the rotor diameter of the optimized DOLSynRM are different from those of a corresponding squirrel cage IM. A DOLSynRM prototype was built and tested. It showed about a 5.4%-unit higher efficiency than the original prototype IM and acceptable starting performance under the rated load condition. The starting capabilities of the motors under study are considered with different loads. The locked rotor apparent power and current stay below permissible limits in both the IM and the DOLSynRM. [ABSTRACT FROM AUTHOR]

In this article, an analytical model to predict the instantaneous torque profile in a synchronous reluctance (SyncRel) machine is developed, which can predict the machine's torque performance based on either inductance or flux-linkage harmonics. High-performance torque-ripple-sensitive applications have stringent torque ripple and noise and vibration requirements to satisfy the overall system requirements. The prediction of the torque ripple is critical in these applications to identify the root cause and then mitigate the torque ripple through design alternations under different loading (current) conditions of the machine. The developed analytical model provides a simpler, intuitive, and significantly less time consuming yet reasonably accurate alternative approach compared to multiple finite-element runs on the same baseline design. The developed analytical model provides design support through fast iterations with design variations or for motor electronic controller implementation. A 2-D finite-element model has been developed to validate the proposed analytical model. The analytical model is also validated with experimental data of a 30-slot four-pole SyncRel machine. [ABSTRACT FROM AUTHOR]

This article deals with the design of a synchronous reluctance (SynRel) motor for full-electric vehicle applications. In particular, the design is focused on “premium” vehicles and aims at the development of rare-earth free electric motor technologies featuring low cost manufacturing. Different solutions are proposed and compared with focus on the rotor design; the investigated topologies employ asymmetric rotor structures with “fluid shaped” barriers without radial ribs to maximize the average torque and minimize the torque ripple. As this choice is very critical for the mechanical strength of the rotor core at high speed, it has been decided to fill the flux barriers with epoxy adhesive resin. The use of the resin requires accurate mechanical analysis in order to assess the rotor robustness at high speed. The article presents the performance of optimized designs without radial ribs and it is focused on the identification of the best properties for an epoxy resin able to enhance the mechanical integrity of the rotor. Moreover, experimental tests on resin cylinder samples have been carried out in order to verify the contact pressure between the resin and a laminated core. The results of this study could be a useful guideline for the designers interested in using this technology for high speed SynRel motors. [ABSTRACT FROM AUTHOR]

In this article, we present a bearingless motor with a novel segmented dipole interior permanent magnet (IPM) slice rotor. The segmented dipole IPM rotor contains a unique pattern of interior permanent magnets arranged to generate a dipole air gap flux pattern. The magnets are encapsulated within an electrical steel rotor structure. The stator contains a three-phase, four-pole winding for suspension and a three-phase, two-pole winding for rotation. We present analyses of several candidate rotor designs. The analyses indicate that the segmented dipole IPM rotor achieves a reduced tradeoff between force and torque capacity and relatively symmetric force dynamics as compared to prior art designs and alternate topologies. Symmetric and decoupled force dynamics allow a simple force decoupling algorithm to be used. We designed, constructed, and tested a prototype system. We experimentally demonstrate that the prototype system can achieve stable levitation and open-loop rotation. [ABSTRACT FROM AUTHOR]

The article presents a torque ripple minimization process using symmetrical rotor flux barrier shaping for synchronous reluctance (SyncRel) machines. High-performance applications demand stringent torque-speed, torque ripple, noise, and vibration requirements to satisfy the overall system performance. An iterative design approach incorporating electromagnetic, structural, and thermal analyses is presented that led to the design of a SyncRel motor with low torque ripple and minimized second-order vibration mode. The contributions demonstrated that the 30-slot, 4-pole SrncRel machine is a viable option for high-performance and packaging-constrained applications. Global response surface method that has the capability for parallel analysis has been used for the multiobjective optimization problem. A 2D finite element (FE) tool with the HyperStudy optimization routine has been used to implement the proposed design process. A quick and easy-to-use motor parameter-based model along with 2D FE analysis is used to evaluate the performance of the optimized design. Experimental results are provided to validate the iterative and comprehensive design, and design procedure. [ABSTRACT FROM AUTHOR]

Mutually coupled switched reluctance motors (MCSRMs) are alternatives in the family of reluctance machines that can overcome switched reluctance motor's (SRM's) system-level integration and control challenges by utilizing standard three-phase voltage source inverters. In this article, a novel segmented-rotor, fractional-slot, tooth-wound MCSRM with notched rotor design is presented, which has very low torque ripple compared to other machine types in the SRM family. The torque ripple is reduced to 3.6% without utilizing any current profiling techniques or torque sharing functions. The ripple minimization is achieved primarily through rotor segment shaping, which has a strong influence on stator flux densities, flux linkages, and torque harmonics. The design strategy, along with the optimization details, is presented for a 120 W, 12 slot-8 pole MCSRM. The designed MCSRM is prototyped for experimental verification and validation of the finite element analysis results and design methodology. [ABSTRACT FROM AUTHOR]

To meet the severe operating conditions in the metal industry, more thorough design and operational assessments about those implemented electric motors for specific applications must be emphasized. With its inherent robust structure, the induction motor is generally adopted to fulfill such driven objective. However, due to global warming and energy conservation concerns, those strictly enforced regulations have potentially increased the complexity and cost of high efficiency induction motor. Since the synchronous reluctance motor (SynRM) has relatively simpler structure with no copper loss in its rotor, it is a very attractive alternative for accomplishing the high-efficiency objectives of those common hoist, punch, roller, and pump applications. In addition, to eliminate drive circuits that can further reduce the overall system construction costs, the rotor barriers of the SynRM can be equipped with direct-on-line capability (DOL_SynRM) with conductors filled in. The impacts to the operational performance of these DOL_SynRMs for different applications will all be thoroughly investigated. The competitive high-efficiency DOL_SynRMs for driving various metal industry equipment can thus be offered. [ABSTRACT FROM AUTHOR]

This article compares the doubly salient permanent magnet machine (DSPMM) having 18/13-pole number combination with 18/17-pole biased flux permanent magnet machine (BFPMM) to verify its improvement in torque characteristics. In such DSPMM, the stator/rotor-pole number combination is 18/13 rather than the conventional one (i.e., 18/12) to achieve balanced three phases, sinusoidal phase flux linkage and back electromotive force (back EMF), small cogging torque, and low torque ripple. On the other hand, an 18/17-pole BFPMM having the similar structure with the 18/13-pole DSPMM is analyzed, which has the best torque performance among such machines with the same stator pole number. To further improve average torque, the inner-type flux focusing (IFC) method is employed in both 18/13-pole DSPMM and 18/17-pole BFPMM. Then, both machines are optimized under the fixed copper loss and envelope size. The comparison shows that both machines have comparably small torque ripple while the 18/13-pole DSPMM with IFC (IFC-DSPMM) exhibits 35% higher torque density and 100% higher ratio of torque to PM volume. An 18/13-pole IFC-DSPMM is manufactured and tested to experimentally validate the predicted results. [ABSTRACT FROM AUTHOR]

Switched reluctance machine (SRM) drive requires a large dc-link capacitor due to the low-frequency harmonics in dc-link current, which is generated during the current commutation between phases. Installing a bulky capacitor bank in the drive has a significant impact on the cost and the overall volumetric power density of the drive. This article analyzes the dc-link current ripple in SRM drive and proposes a control algorithm to reduce the dc-link current ripple while maintaining the machine performance. The proposed algorithm extracts the ripple components from the dc-link current using a high-pass filter. The controller ensures ripple energy circulation between the phases and reduces the pulsating energy requirement from the dc supply. The dc-link ripple is suppressed at a wide speed range of operation to enable efficient and reliable drive operation without adding any external hardware system. Simulation and experimental results are provided to prove the effectiveness of the proposed control technique for both steady-state and transient conditions. [ABSTRACT FROM AUTHOR]

The rotor topologies have a great influence on the vibration characteristics of permanent magnet assisted synchronous reluctance machines (PM-SynRMs). In this article, the vibrations of PM-SynRMs with different rotor topologies are studied and compared. First, the electromagnetic force harmonics of PM-SynRMs have been studied and the design rule about the combination of stator slots and “rotor virtual slots” is given to achieve low vibration. Then, a multiphysics model is established to calculate the vibration of the PM-SynRMs with different rotor topologies. The modal analysis is conducted through finite element method considering the orthotropic of materials and validated by the modal test. Besides, the prototype has been built and the vibration test is performed to confirm the accuracy of the vibration simulation. Based on the multiphysics model, the influence of the shapes of flux barriers and the number of “rotor virtual slots” is investigated. It proves that the design rule about the combination of stator slots and “rotor virtual slots” can achieve low vibration for PM-SynRMs. [ABSTRACT FROM AUTHOR]

With growing interest in electrification in automotive industries, the selection of suitable electric machine types based on application requirements is most important. In this article, three electric machine types, axial flux machine, interior permanent magnet (IPM) machine, and switched reluctance machine, are compared systematically to find the best candidate to drive engine accessories in a hybrid truck. These machine types are designed and optimized to meet the application-oriented design requirements and constraints. An extensive Pugh matrix is created where each machine type is scored based on efficiency range, cost, volumetric power density, gravimetric power density, acoustic noise and stress on the rotor, fault tolerance, heat rejection, and manufacturability. Each Pugh matrix component is assigned to a priority-based weighting, based on the application demand, to determine an accumulated score for each machine topology. A full-scale prototype of the best performing machine type is built and tested. Experimental results validate the multiphysics conclusions drawn in the work. [ABSTRACT FROM AUTHOR]

In this article, a method to evaluate the dc-link capacitor rms current of a switched reluctance motor (SRM) drive under different operating conditions is presented. Square current reference in both hard and soft chopping modes of pulsewidth-modulated current control is considered. By approximating the current controller response and using a recently proposed flux linkage model, the switching-cycle-average phase voltage and current are evaluated over an electrical cycle. The phase voltage and current are further used to obtain the rms values of dc-link current and capacitor current. The proposed method is also used to determine the capacitor current for low-torque-ripple current reference and single-pulse operation. The analytical predictions pertaining to different control methods under different operating conditions are verified by simulation and experimental results obtained from a 4 kW, 1500 r/min, four-phase SRM drive. While the capacitor current is found to be maximum at the lowest operating speed with hard chopping, the maximum capacitor current is observed at an intermediate speed with soft chopping, both for a given magnitude of square wave current reference. The proposed method is useful to size the dc-link capacitor and evaluate its loss in an SRM drive. Furthermore, closed-form expressions for capacitor rms current are also derived, assuming perfect tracking of square wave current reference at low speeds. These expressions bring out the dependence of capacitor rms current on the machine characteristics. [ABSTRACT FROM AUTHOR]

Three-phase line-start synchronous reluctance motor (LS-SynRM) is started by asynchronous torque generated by the rotor conductor bars, and runs synchronously by reluctance torque generated by the inductance difference. In this article, the rotor structure of an LS-SynRM is designed and optimized, based on the theory and characteristics of LS-SynRMs during starting and steady-state operation. First, the influence of the number of rotor flux barriers and the flux barriers ratio on the dq-axis inductance is simulated, and a better structure of rotor flux barriers is obtained. Second, according to the transient theory, a method of separating each torque during the starting process of LS-SynRMs is proposed, and the main reason for the poor starting ability of the initial LS-SynRM is analyzed. Based on the optimized structure of rotor flux barriers, the influence of the area and distribution of the rotor conductor bars on the starting ability of the LS-SynRM is studied, and the structure of rotor conductor bars under the condition of starting with heavy load (constant load) is determined. Finally, through the prototype test, the rated efficiency of the LS-SynRM is 2.8% higher than that of the SCIM is replaced by three phase squirrel cage induction motor (SCIM), which verifies the accuracy of the simulated results. At the same time, the starting current and the pull-in torque under a specific inertia are tested, and the improved effect of the synchronization ability of the improved LS-SynRM was verified. [ABSTRACT FROM AUTHOR]

This article deals with an intelligent grid integrated solar photovoltaic (PV) powered water pumping system driven by three-phase reluctance synchronous motor (RSM) drive. Here, a dc–dc converter is utilized for executing maximum power point tracking algorithm. A voltage source inverter is used for feeding the dc power to a three-phase RSM, from a solar PV array. A three-phase voltage source converter is used at the grid side for a bidirectional power transfer among the utility grid, water pump, and the PV array. This system provides rated water discharge throughout the day despite change in atmospheric conditions and feeds the surplus power to the three-phase utility grid. Moreover, during fault in any of the sources, the performance of the water pump remains unaffected. A high efficiency RSM drive without position/speed sensor is utilized here to drive the water pump. An intelligent power sharing concept, between the PV array and the grid, is used here, in which, automatic switching among all operating modes happens according to the availability of the PV array power and the grid supply. Moreover, the preference is given to the PV array power over the grid supply because of its availability at no cost. This control provides inherent power quality improvement and unity power factor operation at the grid side in all operating modes. The suitability of the system is tested through test results recorded on an experimental setup developed in the laboratory. [ABSTRACT FROM AUTHOR]

Embedded applications like electric and hybrid vehicles are increasingly using electrical machines with a very high power/mass ratio. In this context, the design of such machines, very often operating at high speeds, becomes essential. However, in order to remain economically attractive, these machines cannot use rare earth magnets but at best include (low cost) ferrites. In this context, a significant number of publications have shown that synchronous reluctance machine (SynRM) may be a good choice. However, this type of machine gives poor performances due to the difficulty to get high saliency ratio. This saliency ratio may be improved by the use of low-cost ferrites that saturate the rotor magnetic bridges. The determination of the height of the magnetic bridges becomes then a problem of the prime importance to ensure both high-speed integrity and high saliency ratio. This article proposes a fast model based on the “Beam Theory Method (BTM),” which is intended to be integrated in an electromechanical optimization process. This method will be compared to another one that has been previously introduced for this type of problem: the equivalent ring method. The maximum mechanical stress at critical regions of the rotor of the assisted SynRM can then be calculated for different rotating speeds and rotor iron bridge thicknesses. By adopting the concept of stress concentration, both methods are compared with the results of finite element analyses. Finally, a prototype of the assisted SynRM is used to validate these results from finite element simulations. [ABSTRACT FROM AUTHOR]

Multiobjective and multiload point design optimization of an interior permanent magnet (IPM) synchronous machine using a global response surface method to achieve low torque ripple with high average torque over the entire speed range is presented in this article. The approach consisting of a set of design steps and multiobjective optimization to obtain high-performance electric machines with optimum usage of rare-earth materials for mass production is presented. The design optimization has been applied to a 12-slot eight-pole IPM machine with two different rotor structures to arrive at the optimized design for a variable-speed high-performance application. Motor parameters are extracted under different load conditions to predict the torque/speed performance of the motors. The proposed design approach provides a machine design with maximized output torque, improved torque density, lower torque ripple, and optimum usage of rare-earth materials. Finally, the finite-element-based modeling results are validated with the experimental results. [ABSTRACT FROM AUTHOR]

In the design of modern, high-performance switched reluctance machines, the highly restrictive sets of constraints and requirements severely limit the number of feasible solutions. In order to improve the chances of attaining a successful design, this work proposes a novel and fully analytical approach to the preliminary design analysis. Initially, the correct number of independent design variables is identified. Subsequently, constraints and requirements are introduced one by one, in order to progressively discard all of the unfeasible candidates. At the end of this process, the actual design space is attained, whose main characteristic is to be populated only by feasible candidates. A design case study shows how the proposed methodology allows: 1) to verify the design feasibility; 2) to reduce the number of candidates by orders of magnitude; and 3) to gain useful insight into the design problem and thus select the most convenient strategy to finalize it. As a result, a highly effective design process is attained, so that considerable computational resources can be saved. [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]

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]

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 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]

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]

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]

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]

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]

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]

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]

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]

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]

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 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]

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]

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]

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]

A parametric analysis is carried out to investigate the dependence of the rotor iron losses on the stator and rotor geometry of several synchronous reluctance machines. Six four-pole rotors have been designed with different flux barriers per pole through a multiobjective differential evolution algorithm coupled to a finite-element analysis (FEA). Two different stators with 24 and 36 slots are considered. During the optimizations, a rapid finite-element evaluation has been used to predict the performance of the motors. After that, an accurate time stepping FEA is used for computation of the rotor iron losses. Finally, the interaction between the rotor iron losses and several rotor and stator geometrical parameters is highlighted. The effect of the current time harmonics have also been taken into account, weighting its impact on the rotor losses. [ABSTRACT FROM AUTHOR]