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This article proposes a magnetic flux saturation model that well represents the cross saturation of synchronous reluctance machines (SynRMs) and a parameter estimation method of the proposed saturation model. Existing magnetic flux models do not satisfy the reciprocity condition or express cross saturation well. The proposed flux saturation model consists of terms for self-saturation and cross saturation, and it expresses well the nonlinear relationship between current and flux of SynRMs, as well as satisfies the reciprocity condition. The data of flux saturation are obtained at standstill using the hysteresis voltage injection method. Using the flux saturation data, the parameters of the flux saturation model are estimated. Because the proposed magnetic flux saturation model includes an arctangent function, it is not possible to estimate parameters directly using the linear least-squares method (LSM). However, the proposed parameter estimation method integrates the self-saturation model and transforms it into a polynomial to which linear LSM can be applied. In addition, parameters related to cross saturation are also estimated using linear LSM. Therefore, the proposed parameter estimation method is easy to implement and can be applied to general-purposed inverter products. The effectiveness of the proposed model and its identification method are experimentally evaluated with a 1.5-kW SynRM. Additionally, the identified model is verified with the accuracy of the maximum torque per ampere table and the performance of sensorless control of the tested motor. [ABSTRACT FROM AUTHOR]

This article proposes a novel method to reduce rotor movement when estimating magnetic flux models for interior permanent magnet synchronous motors (IPMSMs) and synchronous reluctance motors (SynRMs). A rotation reduction technique that considers the flux saturation effect is proposed. A hysteresis controller is used to inject voltages only into the q-axis and simultaneously into the dq-axes. The rotation of the IPMSM is reduced by calculating the current at the point where the integral of the q-axis current over time becomes zero. In the case of SynRM, the rotation is reduced by calculating the injection voltage magnitudes such that the oscillation frequency of the q-axis current is higher than that of the d-axis current. The effectiveness of the proposed method was experimentally demonstrated using an 11-kW IPMSM and 1.5-kW SynRM. The proposed technique can be used for the self-commissioning of IPMSMs and SynRMs at a standstill, without rotor locking, or position sensors. [ABSTRACT FROM AUTHOR]

This article proposes a rotor attitude estimation (RAE) method for spherical motors using the multiobject Kalman kernel correlation filter (MKKCF) algorithm in monocular vision. A permanent magnet spherical motor (PMSpM) is adopted as the research object, and a monocular area scan camera is equipped in the RAE system with a visual feature component mounted on top of the rotor output shaft. In the proposed MKKCF algorithm, the Kalman filter is used to enhance the robustness and accuracy of KCF tracker for each object. To simplify the proposed algorithm verification, a one-object tracking comparison is conducted among the KCF algorithm, the fast discriminative scale space tracking (FDSST) algorithm, and the Kalman KCF algorithm, and the results show that Kalman KCF tracker is more applicable for RAE. In addition, an RAE test bench is developed, and the MKKCF-based RAE method and the micro-electro-mechanical system (MEMS) (MPU9250) method are compared when estimating the rotor attitude. To set a benchmark, the contact rotor position measurement with encoders is used. The comparison results indicate that the MKKCF-based RAE method works with higher accuracy than the MEMS method. Finally, a closed-loop PMSpM control experiment is conducted by using the proposed MKKCF-based RAE method, and the practicability of the proposed method is proved. [ABSTRACT FROM AUTHOR]

In this article, we deal with design considerations of a new ac hybrid-excitation permanent-magnet machine with axial stator. Due to the presence of an axial stator, the machine features a typical three-dimensional geometric structure and field distribution. A simplified reluctance-based network is developed to capture the main design features of the machine. The analytical equations are deduced relating the main geometric dimensions to the machine design criteria: speed, power, and flux regulation capability. The influence of key machine geometric parameters, i.e., radial/axial air-gap length, stack length, and bore diameter, on output power, flux density, and flux regulation capability is investigated. It is found that there is a design tradeoff between the machine power density and flux regulation capability. The d/q-axis inductance and its ratio, which has an influence on flux weakening capability and operation performance, is examined. Finally, a 6-pole/36-slot prototype is built. Intensive experimental tests are carried out to verify the machine characteristics. [ABSTRACT FROM AUTHOR]

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

A typical flywheel energy storage system (FESS) includes an electrical machine, a flywheel, and magnetic bearings, which are independent of each other. Therefore, the structure of FESS is complicated, which leads to the problems of high cost and low integration. This article presents a novel stator PM excitation solid rotor machine (SPE-SRM) for FESS, which integrates an electrical machine, flywheels, and a magnetic bearing. The design method of the SPE-SRM is presented specifically. First, the structure and operation principle of the SPE-SRM are illustrated. Second, the design and optimization of the flywheel-rotor are presented with considering of power, energy storage, and mechanical strength. Third, the magnetic equivalent circuit of the SPE-SRM is established to simplify the design. Besides, the armature reaction and leakage flux factor are investigated. Fourth, the performance indexes, including torque, suspension force, no-load back electromotive force (back-EMF), losses, and temperature rise are fully analyzed by the finite element analysis. Finally, a 22 kW prototype is manufactured and tested. The rationality of the concept and design is validated by experiments. The SPE-SRM has the merits of high integration, robust structure, and low cost, so it has the potential for wide application in FESS. [ABSTRACT FROM AUTHOR]

The present article proposes an effective model of synchronous reluctance machines. This model, called the Residual Magnetism (ReMa) model, takes into account not only residual magnetism within the rotor but also that within the stator. Electromotive forces generated by the ReMa model were composed of two frequencies and exhibited similar shapes as those measured in experiments. Resultant equations in a three-phase $(a,b,c)$ frame and in a Park reference frame $(d,q)$ were revealed. The comparison was made with the classical model of synchronous reluctance machine commonly used. Experimental tests were carried out to prove the effectiveness of the ReMa model which was also compared to a classical counterpart in the case where a synchronous reluctance generator was connected to a three-phase diode rectifier. [ABSTRACT FROM AUTHOR]

Dc-field excited modular variable flux reluctance machines (VFRM) are passive salient-pole rotor and independent stator winding, which makes it suitable for aerospace applications. Fault-tolerant operation is commonly required to improve its reliability. Hence, the performance under winding open-circuit faults is analyzed and the fault-tolerant control strategy is presented to increase the output capacity in this article. First, the dc-rectified output voltages and power of the VFRM under both normal and open-circuit faults are derived. Then, phase angle control strategy of the fault-tolerant operation for a 12-slot-14-rotor-pole (12s14r) modular VFRM is proposed, where the control sequence is optimized to achieve the maximum output power of the generation system. Compared with the classical fault-tolerant method, a higher applicability of the proposed method in terms of the types of fault-tolerant operations can be achieved. The electromagnetic properties, including the armature current and the capacity of electrical power output, are analyzed with finite-element analysis. The effectiveness and feasibility of the proposed fault-topology and control strategy are verified by the 12s14r VFRM prototype in normal, fault, and fault-tolerant operation. [ABSTRACT FROM AUTHOR]

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

This article presents a maximum torque per ampere strategy for a five-phase synchronous reluctance drive. The approach is developed considering general machine parameters and is formalized as a constrained optimization problem. The optimal solution is found analytically by using Lagrange’s multipliers method and is based on the computation of the eigenvalues and eigenvectors of the inductance derivatives matrix. The proposed approach is evaluated both numerically and experimentally. It is also compared with other current references control strategies, effectively showing a reduction of the machine rms currents for the same developed torque. The same approach can also be extended to machines with a different number of phases. [ABSTRACT FROM AUTHOR]

This article reveals the flux leakage design and modeling principle of a flux leakage controllable permanent magnet (FLC-PM) machine by considering driving cycles. The key is to obtain the relationship between flux leakage characteristics and multiple operating conditions. Based on the flux leakage controllable concept, an FLC-PM machine with an artfully designed flux leakage region is proposed. The design principle of the machine is investigated by analyzing the magnetic circuit of the machine in multiple operating conditions. The flux leakage factor is introduced to characterize the variable magnetic field in multiple operating conditions. On this basis, the mathematical model of the FLC-PM machine is deduced, and the driving characteristics of the machine are studied in detail. In order to evaluate the presented principle of the FLC-PM machine, a prototype is manufactured for experiments. Through the theoretical analysis and experimental testing, it is verified that the proposed principle is feasible and effective. [ABSTRACT FROM AUTHOR]

In this article, an integrated drive converter of segmented double-stator switched reluctance machine (SDS-SRM) with isolation and nonisolation charging capabilities for electric vehicle (EV) is presented. The proposed converter can not only reduce the number of the power switches, but also implement multiple operation modes. In nonisolation charging mode, the motor windings and existing power switches constitute a buck/boost converter to charge the battery. The appropriate rotor positions are obtained to achieve torque-free control, and the interleaved phase currents control method is introduced to reduce the charging current ripples. In isolation charging mode, the inner-stator is powered by the utility grid to drive the middle-rotor, and converts electrical energy into mechanical energy, while the outer-stator is operated in generation mode to convert mechanical energy into electrical energy. The SDS-SRM is served as a rotating transformer to transfer the electric power to charge the battery with the galvanic isolation function. A low power proof-of-concept prototype platform is built and experiments are carried out to verify the effectiveness of the proposed integrated drive converter and the corresponding control schemes. [ABSTRACT FROM AUTHOR]

In this article, a circulating-current-excited switched reluctance generator system using a standard diode rectifier is proposed and examined. It features a dc power source connected in series with the ring-connected windings, which provides the dc-bias current as the excitation current in the windings. Using a series-connected dc power source, a dc-bias current is easily realized in the ac winding. Compared with the existing machine having dc-bias in the ac winding, the proposed generator can provide dc power with a standard diode rectifier. Less active legs and no rotor position sensor are needed for the control of the circulating current of the proposed generator, which increases the reliability of the generation system. The system configuration and the operation principle are introduced in detail. Then, the electromagnetic performance of the proposed generation system is analyzed at both open-circuit and load conditions. The asymmetric current distributions are deduced and verified by the simulations. At last, the prototype is tested under varied operation conditions and the experiments agree well with the analysis. [ABSTRACT FROM AUTHOR]

Multiphase machines with a prime number of phases (five and seven) have shown better torque density than machines with other phase numbers. Unfortunately, these machines require a special stator design. Hence, this article proposes general rewinding techniques to obtain a five-phase winding from the existing standard three-phase stator frames. The proposed rewinding techniques are applied to construct a five-phase star-connected synchronous reluctance machine (SynRM 1) and a novel combined star-pentagon winding (SynRM 2). Simple mathematical formulations are introduced to compute the equivalent winding factor. The performance of five-phase SynRMs is analyzed using two-dimensional Ansys Maxwell transient simulations under the same copper volume for both healthy and faulty cases. SynRM 1 and 2 provide 6.56% and 13.35% higher torque compared to the three-phase SynRM at rated current and at optimal current angle. The torque ripple is decreased by 17% and 30%, respectively. Moreover, SynRM 1 and 2 offer a better performance at the faulty case; e.g., at one phase opened, the average torque of SynRM 1 and 2 is 82% and 108% higher compared to the three-phase SynRM. In addition, the torque ripple is reduced by about 63% and 81%. Finally, experimental results are done to validate the proposed winding techniques. [ABSTRACT FROM AUTHOR]

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

Vernier reluctance machine (VRM) with dc field coils in stator is a competitive rare-earth-free design for variable-speed industrial applications due to its robust structure and controllable excitation, while its torque density is relatively disadvantageous. To address this issue, this article proposes a new armature winding design method for VRM with dc field coils across two stator teeth. The key is to break the traditional winding design principle based on the flux modulation effect of fundamental dc field harmonic, and instead, reconstruct a novel harmonic winding to enhance the utilization factor of the modulated high-order dc field harmonics arising from the unique magnetomotive force distribution of dc field coils across two stator teeth. By this means, the torque density can be improved by 75.6% against the existing poor counterpart. In this article, the machine structure and operation principle are introduced, with emphasis on the high-order dc field harmonics distribution rule and its influence on the armature winding design. By finite element design and optimization, a comparative study is performed to evaluate the electromagnetic performance of VRMs using two different winding configurations with variable slot pole combinations. A prototype is fabricated and tested, and the results agree well with finite element analysis, which verifies the feasibility and advantages of the proposed winding design method. [ABSTRACT FROM AUTHOR]

Due to the double-layer airgap configuration, the even-order harmonic components exist in the phase back electromotive force (EMF) of flux-modulation electrically excitation double-stator synchronous machine (FMEE-DSM), thus resulting in relatively high torque ripples. To promptly and effectively suppress these torque ripples, this article proposes and implements a second-order iterative learning control (ILC) strategy to minimize the main harmonic torque components based on the periodically repetitive characteristic of torque ripples in the FMEE-DSM. Via harmonic analysis on the torque ripples caused by the cogging torque and the nonsinusoidal induced EMFs, the dominative harmonic component, namely, the seventh-order component, can be precisely identified and then involved in the proposed ILC for torque ripple suppression. To verify the feasibility of proposed control strategy, a test bench of the FMEE-DSM control system was built based on dSPACE 1103. Accordingly, both the static and dynamic performances of the FMEE-DSM were investigated under the conditions of no-load and rated load. The theoretical analysis, computer simulation, and hardware experimentation are given to verify the proposed second-order ILC. [ABSTRACT FROM AUTHOR]

Multiphysics analysis and experimental validation of acoustic noise reduction in a high pole count, high power, switched reluctance machine (SRM), through skewing are explored in detail in this work. An iterative optimization strategy covering electromagnetic, structural, and thermal domains is proposed to investigate the effect of different skewing methods and angles on a 24-stator slot/16-rotor pole (24/16) SRM rated at 100 kW. The contributions of this work are twofold. First, electromagnetic impact, considering average torque, torque ripple, radial and tangential air gap forces, of symmetric and asymmetric skewing on stator and rotor is studied in this work. Second, the impact of skewing methods on acoustic noise and vibration performance is studied and presented in detail. The study reveals that skewing both the stator and rotor by the same amount has superior electromagnetic performance over other types of skewing. Multiphysics simulations conducted, predict a 10.5 dBA reduction in the acoustic noise, compared to a baseline design with no skew, for an optimized rotor-stator skewing angle of 13.75°. Finally, 100 kW prototypes of the baseline and the optimized skewed SRM were constructed and subjected to wide speed range testing. Simulation and test results closely follow each other and validate the effectiveness of the proposed skew design in mitigating acoustic noise and vibration in high pole count SRMs. [ABSTRACT FROM AUTHOR]

In this article, a parallel-series magnetic circuit multi-permanent magnet (M-PM) motor is designed and optimized considering magnet characteristic variation effects, where two kinds of permanent magnets (PMs) are utilized as co-magnetic. Based on the equivalent magnetic circuit method, the detailed design method for the M-PM motor is illustrated. Considering the various operation conditions in potential electric vehicle applications, the B–H curves of two PMs of different typical operation conditions are obtained. Then, a multiobjective optimization method is newly proposed which not only focuses on the magnet characteristics variation effect but also considers output torque, torque ripple as well as antidemagnetization capability under three typical operation conditions. The performances of the initial motor and optimal motor are compared under typical operation conditions. Finally, a prototype machine is built and tested. Both theoretical analysis and experimental results verify the validity of the motor and the proposed design optimization method. [ABSTRACT FROM AUTHOR]

Performance achievable in sensorless control of electrical drives strictly depends on the adopted synchronous machine. The combination of cross-saturation and saliency, both dependent by the current load and the rotor position, makes always the position estimation afflicted by an estimation error. When the machine is highly saturated, the sensorless control can even diverge resulting in a useless drive. Thus, it is of primary importance to know in advance the convergence region of the sensorless drive, i.e., the operating points, where the motor can be successfully controlled without a position sensor. The aim of this article is to show how to compute the estimation error, the saliency, and the convergence region (hereafter called self-sensing capabilities) starting from the flux linkages maps or, more generally, from the incremental inductances. The dependence on the rotor position is also considered. Finite element simulations and experimental measurements validate the proposed model. The code used to compute the self-sensing capabilities is available as an open source package. [ABSTRACT FROM AUTHOR]

This article presents a method to reduce the torque ripple in an 8/6 four-phase switched reluctance motor (SRM). The proposed scheme introduces a nonlinear modulating factor dependent on the rotor position and magnitude of the phase currents. This factor manipulates the currents in two adjacent phases during commutation and reduces the torque ripple effectively. Unlike the conventionally available torque-sharing functions, the proposed method instantaneously modulates every phase current obtained mathematically based on the other phase current in order to maintain the net torque constant. The proposed method requires minimal offline analysis and offers maximum possible torque with a minimal ripple. The method is simple and easy to implement due to a low computational burden. The proposed algorithm is implemented using MATLAB/Simulink software and is also validated experimentally on a 0.6-hp 8/6 SRM using a field-programmable-gate-arrays-based hardware setup developed in the laboratory. Typical results are presented and compared with the existing techniques. A torque ripple of $\approx 8\%$ has been achieved. [ABSTRACT FROM AUTHOR]

This article investigates the design methods and performance optimization of segmented-double-stator switched reluctance machine (SDS-SRM). First, two segmented U-shaped single-stator SRMs are introduced, including inner-rotor and outer-rotor constructions. In order to enhance the torque and power density, these two kinds of single-stator SRMs are combined together to constitute an SDS-SRM. Then, the relationships of torque ripple coefficient with the mechanical offset angles of the inner and outer rotor teeth are investigated to obtain the optimal rotor structure, and the corresponding conduction phase sequences for double-stator excitation mode are also analyzed. Furthermore, the flux distributions of the inner and outer stators with different coil magnetic polarities configurations are researched, and it reveals that the phase windings both on inner and outer stators with NSSNNSSN polarities have better magnetic field decoupling characteristics. To evaluate the final topology of the proposed SDS-SRM, the static magnetic characteristics and dynamic performances are presented. Finally, the SDS-SRM prototype is manufactured and tested to validate the theory and simulation analyses. [ABSTRACT FROM AUTHOR]

This study investigates the influence of inner reluctance rotor topologies configurations on the electromagnetic performances of coaxial reluctance magnetic gears (CRMGs). It considers flux barrier (FB) rotor topology, as well as the salient pole (SP) rotor. Both SP and FB topologies are optimized by means of different salient shapes and novel supershape formula, respectively. The CRMG performances in terms of torque density and cogging torque have been investigated and optimized fairly by using 3-D finite element analysis. With an appropriate rotor topology, FB-CRMG can achieve higher torque capacity and lower cogging torque in comparison with SP-CRMG topologies. The prototype of optimized FB-CRMG has been built to validate the predictions of output torque quality, its loss, and efficiency. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method (AM) based on the air-gap magnetomotive force (MMF) permeance model is proposed to predict the nonlinear instantaneous torque of switched reluctance machines (SRMs). The analytical expression of the air-gap MMF is first obtained from the winding function and current profile, while the air-gap magnetic permeance considering the double-sided slotting effects is also derived. Then, the nonsaturated field distribution along the air-gap circumference is presented based on which the instantaneous torque can be calculated from the Lorentz force law. Furthermore, the model is enhanced with a saturation distribution factor to include the nonlinear characteristics. The proposed method is free from preliminary data or empirical coefficient and benefits from the simplified model and solution. The AM will be validated by the two-dimensional finite-element method based on four SRMs with different structures. Moreover, an SRM prototype is manufactured for experimental verification. [ABSTRACT FROM AUTHOR]

For traditional 12/8 bearingless switched reluctance motors (BSRMs), the coupling between torque and levitation increases the complexity of control. For the turbomachinery application, 2 degrees of freedom (DOF) BSRMs stabilized by extra 3-DOF active magnetic bearings are required. In this article, an improved BSRM with 4 rotor poles and 12 stator poles is proposed to realize 4-DOF radial levitation, and the torque dead zone is compensated because that two rotors and these poles are assemble with 15 mechanical degree shifted. The decoupling of torque and radial levitation is realized simultaneously. Moreover, the operation principle of axial reluctance force is analyzed for passive levitation in the axial direction. Various experiments were completed to verify the performance of the proposed BSRM, and the prototype achieved stable levitation of the rotor in 10 000 r/min. [ABSTRACT FROM AUTHOR]

In order to improve the performance (low torque ripple, low suspension ripple, and high power factor) of the permanent magnet assisted bearingless synchronous reluctance motor (PMa-BSynRM), the multiobjective optimal design based on fast nondominated sorting genetic algorithm (NSGA-Ⅱ) of PMa-BSynRM rotor topology is investigated in this article. First, the structure and operation principle of the PMa-BSynRM are introduced. Second, the initial rotor design that gives optimizer the ability to produce a variety of barrier shapes and the comprehensive sensitive analysis that evaluates the influence of each design variable on optimization objectives are presented. Third, the optimal design is selected from the Pareto front, which is generated by NSGA-Ⅱ, and validated by finite-element analysis. The simulation results confirm that the torque and suspension force capacity of optimal motor are improved significantly in comparison with initial design, whereas the value of power factor reaches 0.81. Finally, the optimal prototype motor is manufactured, and experimental results confirm the validity and superiority of the optimized design. [ABSTRACT FROM AUTHOR]

In this article, split-tooth stator slot permanent magnet (PM) machines, which have high fault-tolerant capability, are proposed. Compared with the existing 12-slot 10-pole (12S10P) stator slot PM machine, the torque can be improved by 66% by properly choosing the split tooth number and other geometric parameters. It is found that two split teeth stator slot PM machine (ST2) shows the best torque characteristics among the stator slot PM machines with different split tooth number. To further illustrate the merits and demerits of ST2, a conventional 6S4P surface mounted PM machine (SPMM) and a 6S4P variable flux reluctance machine serve as the benchmarks to compare with the 6S11P ST2, at both open circuit condition and load condition. The 6S11P ST2 shows 68% higher torque over the 6S4P VFRM. Although the torque of the 6S11P ST2 is around half of the 6S4P SPMM, the former has 70% higher torque per PM volume than the latter. Furthermore, demagnetization analyses under three-phase short-circuit and pure d-axis currents show that the 6S11P ST2 has much better demagnetization withstand capability over the 6S4P SPMM. A Prototype is manufactured and tested to validate the theoretical analyses. [ABSTRACT FROM AUTHOR]

In this article, we developed an improved hybrid field model (IHFM) to predict the on-load performance of the interior permanent-magnet (IPM) motors considering both iron saturation and slotting effect. It combines the airgap analytical model based on the modified conformal mapping with the reluctance mesh method for stator and rotor. The reluctance mesh method can accurately predict the rotor saturation and tooth-tip saturation even their field distribution is complicated due to the armature reaction. Besides, IHFM will significantly accelerate computation speed using the analytical model for airgap region while keeping high accuracy. The finite-element analysis and experimental results of the flat-type and V-type IPM motors are demonstrated to verify the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

Currently, surface-mounted permanent-magnet (PM) rotors are more frequently employed than interior PM rotors in high-speed PM motors. It is mainly because the mechanical strengths of sleeve materials can be much higher than those of silicon steels. However, at high speeds, the current harmonics caused by pulsewidth modulation (PWM) converter induce high eddy current losses in PMs and sleeves when they are conductive. Moreover, because of the existence of nonmagnetic sleeves, the surface-mounted PM motors have very poor flux weakening abilities. Interior PM motors can not only avoid sleeves, but also reduce the influence of the PWM converters. Moreover, they can provide additional reluctance torque and have better flux-weakening abilities. A major drawback of interior PM rotors is their low mechanical strengths, which limit their surface velocities. In this article, high mechanical strength amorphous metal 2605SA1 is used to increase the surface velocity of an interior PM rotor. A surface-mounted PM rotor protected by carbon-fiber sleeve is designed to perform a comparison study. Both motors are built and tested. The advantages and disadvantages of the two motors in terms of mechanical, electromagnetic, and thermal behaviors are evaluated. [ABSTRACT FROM AUTHOR]

Based on the characteristic of doubly salient electromagnetic machines (DSEMs) that the incremental inductance varies with the rotor position, a sensorless startup strategy is proposed in this article. First, the pulse injection based method is adopted to estimate the initial rotor sector. The influence of the field current on the position estimation error is analyzed. Second, the startup method with no test pulse is introduced to start DSEM. Two key strategies are proposed: the commutation strategy based on the series incremental inductance detection and the anti-out-of-step control strategy based on the circulating current detection. The series incremental inductance is estimated in a chopping period and is compared with a preset threshold to obtain the commutation signal. The circulating current of the nonconducting phase is detected to monitor whether the DSEM is out of step. Furthermore, the current chopping mode is optimized, which has influence on the circulating current of the nonconducting phase. The proposed strategy can avoid the discontinuity of phase current caused by the test pulse in the existing technique. Finally, the effectiveness and the feasibility of the proposed method are verified by a series of experiments on the 9-kW 12/8 pole DSEM prototype. [ABSTRACT FROM AUTHOR]

In order to combine the advantages of modularity and hybrid-excitation for motor torque and power density enhancement, this article proposes a 12/4 modular-topology, permanent magnet (PM) assist, hybrid-excitation switched reluctance machine (HESRM) with both segmented-stator and -rotor. The machine topology and basic operating principle are presented. Three key parameters of the machine are optimized for assessment on the torque production. The three-dimensional finite-element analysis is employed to consider the effects of end winding and core saturation. The static magnetic characteristics and dynamic performances are simulated and compared with a 12/4 segmented SRM (SSRM) without PM and a 12/10 segmented-stator HESRM. Two prototypes of the proposed 12/4 HESRM and a 12/10 segmented-stator HESRM with the same size are manufactured and developed for experimental verification. Both results show that the proposed motor can achieve higher dynamic average torque and higher power/torque density at high-speed operation. It also has a stronger starting capability, more rapid response for command changes, as well as better stability and tracking features. [ABSTRACT FROM AUTHOR]

This article proposes a new asymmetric modular permanent magnet assisted synchronous reluctance motor (PMaSynRM) to offer low torque ripple and high reliability. First, the stator is segmented into three modules without magnetic coupling. The influence of flux gaps between modules is investigated on torque performance. For the torque improvements, the multilevel optimization strategy is conducted, which simultaneously enhances the fault-tolerant capability. Besides, the torque ripple reduction methods are proposed with the asymmetric rotor and shifted end-slots. The analytical formulae of asymmetric flux barrier angle are derived. Then, the asymmetric flux barrier is designed to reduce the 12th harmonic, and the end-slots are shifted to minimize the additional 2nd harmonic component caused by flux gaps. Finally, the enhanced fault-tolerant capability of the proposed modular PMaSynRM is also evaluated. The effectiveness of the proposed approach is verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

In this article, a high-precision equivalent magnetic circuit (EMC) model is first proposed for slotted permanent-magnet (PM) limited-angle torque motor (LATM) with nonuniform teeth, which leads to potential application in swing system substituting a lower torque density of the slotless structure. By the proposed relatively fine division method of magnetic reluctance in the stator tooth-tip segments, air-gap regions, and PM poles, the proposed EMC model can fully consider armature reaction and magnetic saturation problem. Subsequently, a multiobjective optimization method based on the EMC model is proposed to improve torque performance. Finite-element analysis is employed to validate the EMC model and optimization results. Following that, a curved nonwounded tooth shape is carried out and further optimized to decrease magnetic saturation of stator teeth and significantly improve symmetry of torque profile about stable equilibrium point, compared with the traditional straight tooth shape. Finally, the slotted LATM with curved teeth is prototyped, and its experimental results are presented and discussed. The simulation and experimental data show better accuracy of torque profile improvement. [ABSTRACT FROM AUTHOR]

In this article, a variable flux reluctance machine (VFRM) with dc field excitation and modular structure is proposed and it exhibits controllable flux, simplified manufacture, better fault tolerant capability, and potentially reduced material consumption. Its operational theory is illustrated by using flux modulation principles, and the working harmonics considering the modular structure are analyzed. Besides, the winding factors of modular VFRM are derived considering the flux gap width. The parameters are optimized by two-dimensional finite element method to maximize the back electromotive force (back-EMF) and the ratio of phase self-inductance to mutual inductance. Moreover, the electromagnetic performance including open circuit air-gap flux distributions, open circuit air-gap flux densities, flux linkage, back-EMF, inductance of armature windings, output characteristics, loss, power factor, and efficiency-map are compared for 12s10r and 12s14r nonmodular and modular VFRM. Additionally, the fault including short circuit and open circuit fault are analyzed. Finally, a modular 12s14r VFRM prototype is manufactured and tested to validate the theoretical and finite-element analyses. [ABSTRACT FROM AUTHOR]

This article deals with an improved control for synchronous reluctance motor (SyRM)-based photovoltaic (PV) water pumping system, eliminating the speed controller of position sensorless field-oriented control (FOC) of SyRM. The solar water pump drive involves two stages of power conversion. The reference quadrature axis current of FOC is estimated from available PV array power that is being continuously tracked for maximum power point. This eliminates the requirement of an additional speed controller. This improves the transient behavior of overall control under dynamic conditions such as varying solar radiation. A pole is eliminated from overall characteristic equation of open-loop dc link voltage control transfer function. As a result, a single proportional integrator controller satisfactorily controls the whole pumping system. The system is much easier to tune, and by default, immune to aging and variation in pump's constant. This improves fidelity and reduces the overall cost of the system. Performance of this system is validated through a developed laboratory prototype of solar PV array-fed SyRM drive for water pumping. The overall system performance is examined under different environmental conditions. [ABSTRACT FROM AUTHOR]

In this article, a novel dual-consequent-pole transverse flux motor and its analytical model are proposed. Differ from existed transverse flux machines, the proposed motor owns core-tooth-to-magnet types of the consequent-pole configuration on both stator and rotor. This unique motor configuration improves the no-load permanent magnet flux linkage interlinking with armature winding, thus leading to an enhanced torque density. The structure and working principle of the proposed motor are introduced as the first half part. Then, based on the combination of equivalent magnetic circuit method and subdomain method, an analytical modeling method is proposed to estimate the electromagnetic performance of the proposed motor. The parameters of the equivalent magnetic circuit model, e.g., the magnetomotive force and reluctances are calculated based on the subdomain model technique, considering the influence of the cores’ saturation and the axial end effect during calculation. Based on the magnetic field distribution result, the electromagnetic performance is estimated. The analytical results are verified by both the finite-element method and the prototype experiment. [ABSTRACT FROM AUTHOR]

This article presents a simple analytical model for the sizing of synchronous reluctance (SynRel) machines. The accuracy of the method is achieved by modeling a simple rotor geometry that presents all the characteristics of a real machine. The analytical equations proposed are able to guarantee accurate and fast results during the preliminary design of the machine. A generalized sizing approach, based on the saliency ratio, is presented in detail. The method is flexible and can be adapted for any SynRel machine. The accuracy of the proposed model is validated for a range of operating conditions, comparing the results with both finite element simulations and experimental measurement carried out from an existing four poles SynRel 15-kW prototype. [ABSTRACT FROM AUTHOR]

In this article, we present a dual-stator structure-parallel fault-tolerant machine (DSSPFTM). In this machine, the radial-flux dual-stator structure with a higher density is adopted to the fault-tolerant system. For better performance in fault condition, the combination of permanent-magnet component (PMC) and reluctance component (RC) in the rotor and large-opening slot is proposed. Because of the same poles and torque-variation principle, the PMC and RC are combined. The PMC is devised to supply most of the torque in normal conditions, while the RC provides enough self-inductance for limiting current under short-circuit (SC) occasion. Most of the flux leakage is separated from the active flux and the overload ability is improved. The design process of DSSPFTM is described in steps and details. Based on the fundamental of maximum torque under normal conditions, PMC and RC are integrated together. The end flux leakage originating from the adjacency of RC to PMC and the effect of RC length on torque are analyzed. The back-EMF, torque, inductance, loss, efficiency, and SC analysis are demonstrated. The stress and deformation distribution of the rotor and the comparison with the traditional structure are conducted. A prototype DSSPFTM is designed and manufactured. The experiments accord with simulations, indicating that the DSSPFTM with fault tolerance can improve the torque density effectively. [ABSTRACT FROM AUTHOR]

The synchronous reluctance motor is becoming a very attractive alternative to the ac induction machine. This is due to the lack of rare-earth metals in their construction and a higher efficiency, which was brought about by recent progress in rotor design. However, in order to achieve an efficient and low-cost operation of the synchronous reluctance motor drive, an adaptive sensorless algorithm should be utilized to cope with machine nonlinearities. This article describes an adaptive observer, which can provide an estimation of rotor position and speed, as well as core loss and inductance parameters. A modified pulsewidth modulation (PWM) switching scheme and a current derivative measurement method are proposed, together with an extended Kalman Filter design. Experimental results are shown to demonstrate the method performance and feasibility. [ABSTRACT FROM AUTHOR]

Finite-set model predictive current control (FS-MPCC) has been employed for machine drives owing to the good dynamic performance. Sensitivity to parameter variation is one of the main barriers to its widespread application. To overcome this barrier, this article proposes an improved FS-MPCC for surfaced permanent magnet synchronous machines (SPMSMs). The contribution of this article is developing a novel current update mechanism, where the variation of resistance, rotor flux linkage, and inductance is considered, in which a modified coordinate system that contains a stationary and rotary axis frame is introduced. In this case, the predicted parameter can be obtained more accurately based on this mechanism, which can suppress the disturbances caused by model parameter mismatch. In addition, SPMSM parameter mismatch effect on FS-MPCC performance is analyzed in this article, which testifies that resistance mismatch influence on current prediction error can be neglected in practical system. The proposed FS-MPCC is validated and compared with different state-of-the-art methods. Improvement of the proposed control strategy is validated by means of experimental results on a 2-kW test rig. [ABSTRACT FROM AUTHOR]

Permanent magnets (PMs) have been widely used in different types of electrical machines to improve their performance. This article introduces a novel multi-tooth hybrid-excited switched reluctance motor (MT-HESRM) with PMs placed between the end teeth of the adjacent modules. Thanks to the innovative method of embedding PMs, a unique design is developed. First, the operating principle of the motor is explained, and the magnetic circuit model of the motor is analyzed. The magnetic characteristics in terms of flux density, flux linkage, inductance, and torque are obtained and compared with those of its PM-less counterpart. The mathematical model of the reluctance and PM torques is presented. The reluctance and PM torques are decoupled using the finite-element analysis, and the torque contribution of the PMs is discussed. The steady-state operations of both motors with both current chopping and single-pulse controls are analyzed and compared under different speeds. Finally, both motors are manufactured, the laboratory tests are done, and the experimental results are extracted. Both the simulation and test results elucidate that the MT-HESRM, which has only three small PMs as auxiliary flux sources, has unique features in terms of high output power and torque with a negligible cogging torque. [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]

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]

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 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, 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]

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 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]

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]