Search

This paper presents the comparisons between two types of switched reluctance machines (SRMs) and SRM converters. An SRM with a segmental rotor is compared with a conventional SRM (CSRM), and an SRM converter containing a passive boost circuit is compared with a conventional asymmetric half-bridge (AHB) converter. The segmental SRM has an asymmetric rotor with a segmented structure. The four rotor segments are made of steel laminations. Two segments are misaligned with the other two by 15 degrees. The torque ripple of the SRM with this structure is decreased, and the static torque is increased compared to a conventional SRM. The boost converter comprises a front-end circuit and a conventional AHB converter. The front-end circuit boosts the voltage level. The boosted voltage accelerates the rising and falling progress of the phase current. In this way, the SRM can obtain a greater speed and a smaller torque ripple. The comparison is conducted in simulation and validated through the experimental results. The experiment results have demonstrated that the segmental SRM obtains a maximum 7% torque ripple reduction at a low-speed range, compared to the CSRM. With the boost converter, both the CSRM and the segmental SRM can achieve a lower torque ripple and a higher maximum speed. [ABSTRACT FROM AUTHOR]

In this article, a switched reluctance machine (SRM) with six phases and a misaligned segmental rotor is proposed. The segmental rotor has an internal 15-degree misalignment, allowing the SRM structure to be a one-layer 2D structure with a short flux path structure. The proposed SRM produces a relatively low torque ripple by exciting two phases simultaneously. Additionally, an optimization method is applied, allowing for the maximum torque position of one phase to be aligned with the zero-torque position of the adjacent phase. The finite element method (FEM) is used to analyze and design the proposed SRM and to simulate the proposed liquid cooling system. The static torque waveforms are analyzed, and the dynamic torque waveforms are simulated with a drive using SiC MOSFETs. Finally, a prototype is manufactured, and the experiment is performed to validate the design and simulation results. [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]

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]

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

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

Phase inductance is a key parameter in the design of switched reluctance machines (SRMs) because the torque, torque ripple, losses, and the dynamics of phase voltages and currents are related to the phase inductance. Therefore, accurate calculation of the inductance profile of an SRM is important in determining the SRM behavior. Instead of using the time-consuming finite element analyses (FEAs), or the analytical methods that require prior knowledge of flux linkage from either an FEA simulation or an experimental test such as the curve fitting and flux path based methods, this paper proposes a fast and accurate analytical approach to determine the phase inductance of an SRM with any common topologies, dimensions, and phase currents at any rotor position. In the proposed approach, the magnetic field distribution and the permeance parameters in the air region are first determined by solving the partial differential equations of magnetic potentials based on Maxwell's equations. The air-region permeance parameters are then substituted into a magnetic circuit network to include the impact of the saturation effects of steel on the phase inductance profile. The agreement between the results of the proposed analytical method and two/three-dimensional FEAs and experimental results validates the analysis. [ABSTRACT FROM AUTHOR]

Compared to nonmodular machines, modular topologies become increasingly attractive due to their simplified manufacture process, better fault-tolerant capability, and potentially reduced material consumption. In order to maintain or even enhance the machine performance while achieving high fault-tolerant capability, novel modular, single-layer winding switched reluctance machines (SRMs) with different pole numbers are proposed, which are supplied by rectangular wave current with different conduction angles. The influences of the pole number and flux gap width between E-core segmented stators on the electromagnetic performance have been investigated in terms of self- and mutual inductances, electromagnetic torque, copper loss, iron loss, and radial force. It has been found that the modular structures with higher rotor pole numbers than stator slot numbers (12-slot/14-pole and 12-slot/16-pole SRMs) can maintain and even improve the average torque due to the nature of self and mutual inductances. In addition, the torque ripples for modular machines are significantly reduced (below 50%), so do the iron loss and radial force, leading to higher efficiency albeit with potentially lower vibration and acoustic noise. Two prototypes with 12-slot/8-pole and 12-slot/14-pole combinations have been built with both nonmodular and modular structures to validate the predictions in terms of inductances and static torques. [ABSTRACT FROM AUTHOR]

This paper presents a simulation by finite element analysis of the switched reluctance motor, using a half bridge asymmetric converter, in order to verify the flux densities in the ferromagnetic parts of the motor to avoid a high level of saturation. The results obtained from the simulation shows that the motor operates under the saturation point of the stator as well as the rotor materials. [ABSTRACT FROM AUTHOR]

This paper proposes an advanced dynamic modelling approach of the mutually coupled switched reluctance motor (MCSRM) in the $dq$ reference system that can consider saturation, cross-coupling, and spatial harmonics. Different topologies and their operating principles are investigated and an idealized $dq$-model considering the inductance harmonics is derived. A dynamic model is built based on flux-current lookup tables (LUTs) obtained from finite element analysis (FEA). A simplified method to inverse the two-dimensional LUTs is proposed. A fast computation approach is used to reduce the number of FEA simulations and calculation time to obtain the LUTs. Motor dynamic performances at different speeds are simulated by using the proposed dynamic model and the results are investigated and verified by FEA. The motor dynamic behavior can be accurately obtained in a short simulation time by using the proposed approach. Experiments are carried out on a 12/8 MCSRM, showing good accuracy of the proposed model. [ABSTRACT FROM AUTHOR]

Applications of switched reluctance machine (SRM) are increasing in the industry due to their many desirable features. This study proposes a hybrid analytical model (HAM) of the SRM for the hardware‐in‐the‐loop (HIL) simulation. To obtain satisfactory accuracy, the phase flux linkage is solved by the magnetic equivalent circuit (MEC) method when the stator and rotor poles overlap, and by the space harmonic method (SHM) when the poles do not overlap. The backward Euler and Newton–Raphson methods are used to calculate the exciting current, while the Gaussian quadrature is used to compute the electromagnetic torque in the HIL simulation. The digital hardware implementation of computation components are developed on the field‐programmable gate array by exploiting the parallel hardware architecture and fully pipelined arithmetic processing. To highlight the performance of the HAM, the captured real‐time results are compared with the off‐line transient solution obtained through the co‐simulation of Ansys Maxwell®, Ansys Simplorer®, and Simulink®, which model the SRM, drive circuit, and control system, respectively. [ABSTRACT FROM AUTHOR]

This paper proposes a combined modeling method for switched reluctance machine (SRM) with few samples of flux linkage characteristics measured without rotor clamping devices and position sensors. The proposed method mainly consists of two steps, namely data reconstruction and characteristic description. In data reconstruction, the entire flux linkage characteristics are obtained by training support vector machine (SVM) with the measured few samples. The characteristics from the trained SVM are consistent well with those from the rotor-clamping measurement. In characteristic description, back-propagation neural network (BPNN) is adopted to describe the reconstructed flux linkage characteristics and calculated static torque characteristics. On this basis, the simulation model of the SRM prototype is built in MATLAB. The results from simulation under both motoring and generating mode are compared with those from experiments, and good agreements can be found, which prove the effectiveness of the proposed modeling method. To further demonstrate the accuracy and application of the entire flux linkage characteristics obtained from data reconstruction, BPNN is used again to build the mapping from flux linkage and phase current to rotor position for rotor position estimation, and some results are presented. The applicability of the proposed method to different SRM topologies is discussed as well. [ABSTRACT FROM PUBLISHER]

The symmetric structure conventionally used in two-phase switched reluctance machines (SRMs) leads to dead torque zone and issues with startup. When a phase is at the fully aligned position with respect to the rotor, the complimentary phase is completely unaligned. Within this region, excitation of either phase fails to generate sufficient startup torque. Significant research has been focused on the design of machines with large, unidirectional startup torque specific to the direction of rotation required by the given application. In this work, a conventional two-phase SRM is analyzed to reveal the underlying geometric constraints leading to startup difficulties. To overcome this, a phase shift design strategy is proposed to ensure both large starting torque and bidirectional startup capability. The design is investigated and validated through both simulation and experiments, and the results show the validity of this new configuration. [ABSTRACT FROM PUBLISHER]

The half-teeth-wound switched reluctance machines (HT-SRMs) having single-layer concentrated windings, feature simpler structures since the coil number is half, and phase-to-phase insulations in slot are eliminated. To evaluate the effects of winding configurations, the electromagnetic performances of HT-SRMs and conventional full-teeth-wound SRMs (FT-SRMs), including air-gap flux density, coil and phase flux linkage, inductance, torque, volt–ampere, and radial magnetic force (RMF), are comprehensively compared. The results based on theoretical analysis and finite-element (FE) method reveal that HT-SRMs would exhibit higher torque per ampere when the magnetic saturations are not too severe, whereas require higher voltage supply and generate more significant RMF. Further, it is found that the fault-tolerant capabilities of HT-SRMs are superior to FT-SRMs. A pair of prototypes with identical laminations but different winding configurations are manufactured and the experimental results confirm the predictions. [ABSTRACT FROM PUBLISHER]

A new toroidally wound switched reluctance machine (TSRM) with a single continuous multitapped winding is presented. This machine may be driven by a 6-switch asymmetric converter that supplies unipolar coil currents or by a 12-switch voltage source converter that supplies bipolar coil currents. The TSRM magnetic design and power electronic control is described, and its performance is compared with a conventional switched reluctance motor (CSRM) and with a previously reported toroidal format switched reluctance machine that utilizes six discrete winding coils in a three-phase wye connection (WSRM) driven by a voltage source inverter. A fixed 6–4 CSRM magnetic circuit design is selected for the comparative analysis of the three machine topologies by static and dynamic finite-element simulations. [ABSTRACT FROM AUTHOR]

This paper proposes a new fast method to determine the entire flux-linkage characteristics of a switched reluctance machine (SRM), which are critical for performance estimation and advanced control of the machine. The proposed method mainly consists of two steps, namely, measuring and calculating. In the measuring step, the flux-linkage characteristics of the SRM are measured at four specific rotor positions by a new indirect method without rotor clamping devices and position sensors. The magnetic coupling among phases is considered to improve the accuracy of measurement. In the calculating step, based on the measured results, the analytical expression of the flux-linkage characteristics is proposed, which only needs a few coefficients. With the expression, the flux-linkage characteristics at any rotor position can be calculated. The entire flux-linkage characteristics of a 1-kW three-phase 12/8-pole SRM obtained by the proposed method and traditional rotor clamping method are compared, and a good agreement can be found, which verifies the feasibility and accuracy of the proposed method. Furthermore, with the entire flux-linkage characteristics calculated by the proposed analytical method, the dynamic performances of the SRM prototype under both motoring and generating modes are simulated and compared with those from other methods and experiments, which further verify the accuracy of the proposed method. [ABSTRACT FROM PUBLISHER]

With the era of modern vehicle electrification, electric machines with high traction torque–speed output and compact volume are highly desired. This paper presents a family of switched reluctance machine configurations that are composed of double rotors and one stator integrated in one machine housing. The machines are potentially more compact and lower cost, while providing two independent mechanical outputs suitable for hybrid electric vehicle transmissions. The detailed design process of a double-rotor switched reluctance machine (DRSRM) is presented, comprising of analytical calculations, finite-element field analysis, and full-drive system simulation. Additionally, some optimizations are applied to maximize the machine performance and minimize the machine weight and volume. A scaled prototype machine is designed and built according to chosen vehicle drive cycles to evaluate and validate the DRSRM prototype. [ABSTRACT FROM AUTHOR]

In this paper, a fast and accurate analytical method is proposed to analyze the loss and efficiency of switched reluctance machines (SRMs) under various operating conditions. The analyses are applied on a four-phase 16/12 SRM with high power density and wide speed range, which was designed for traction application. A direct method is proposed to calculate hysteresis and eddy current loss without empirical equations. The machine is discretized into a limited number of elements according to the magnetic flux density distribution using an analytical magnetic circuit method. Variable loss coefficients are used for each element to improve the accuracy. The developed method has been validated with simulation and experimental results. [ABSTRACT FROM PUBLISHER]

Switched flux permanent magnet (SFPM) machines have significant potential for many industrial applications because of their doubly salient structure, similar to switched reluctance machines. In recent years, several novel SFPM machine topologies, such as multi‐tooth, E‐core and C‐core, have been developed to reduce the usage of permanent magnet materials without sacrificing the torque capability. A comparative study of the electromagnetic performance of these topologies, together with conventional SFPM machines having different stator/rotor pole combinations, that is, 12/10, 12/13 and 12/14, is presented. In addition to open circuit and electromagnetic torque performance, their torque–speed characteristics are investigated and compared. It is found that for conventional SFPM machines, the higher the rotor pole number, the better the flux‐weakening capability, and higher maximum speed can be achieved. In contrast, owing to high d‐axis inductance in the multi‐tooth, E‐core and C‐core machines, infinite maximum speed can be obtained. Moreover, among all these machines, the multi‐tooth machine has the highest flux‐weakening factor, while the E‐core machine exhibits the largest power capability. In addition to two‐dimensional (2D) finite‐element analysis (FEA), 3D‐FEA is also performed accounting for the end effect. Finally, the torque–speed characteristics of prototype SFPM machines are measured to verify the FEA. [ABSTRACT FROM AUTHOR]

In this paper a novel modular switched reluctance machine (SRM) with E-core stators and segmental rotors is presented. Unlike the conventional SRMs, there are hybrid radial and axial magnetic paths in the E-core stators due to the particular construction. An approximate and simplified 2D finite-element analysis (FEA) model is proposed to calculate its magnetic characteristics and compared with 3D FEA model results. A comparison of the static magnetic characteristic and dynamic performance between the modular SRM and a conventional SRM is made to emphasize the superiority of this novel SRM. Furthermore, the fault tolerant performance of this modular SRM under open-circuit faults is also presented. Finally, a prototype machine is built and tested in the laboratory. The flux linkage characteristics are experimentally obtained by indirect method and are compared with FEA results. Other experimental results such as single-pulse operation, closed-loop control operation, fault-tolerant operation at open-circuits and sudden change in load torque operation are also presented to validate the analytical and simulation results of the modular SRM and its performance. [ABSTRACT FROM AUTHOR]

Switched reluctance machines (SRMs) suffer from ultra-low-frequency torque ripple in single pulse mode. This ripple is the result of an imbalance in phase currents, when multiphase excitation occurs. This paper investigates the origin of this imbalance and identifies the imbalanced phase. Excitation shifting strategy, which delays excitation of the imbalanced phase, is then proposed. The delay angle adjusts current amplitude in the imbalanced phase to attain a perfect balance between all phases. The excitation shifting strategy is a general solution, which is applicable to both three-phase and four-phase machines. In addition, the proposed method can be implemented by a much simpler drive structure, when compared to the existing balancing methods. Hardware measurements are provided to verify superior performance of the proposed current balancing technique. [ABSTRACT FROM PUBLISHER]

In this paper, novel variable flux reluctance machines (VFRMs) with different rotor pole numbers, which employ a doubly salient structure together with field windings identically located in the stator for each phase, are investigated and compared. Different from other doubly salient machines, such as switched reluctance machines (SRM) and doubly fed doubly salient machines (DFDSM), the equation for determining the stator/rotor pole numbers, i.e., Nr=Ns\pm 2k, is no longer limited in VFRMs. More feasible selections of rotor pole numbers can be used if the stator/rotor pole numbers can satisfy Nr\ne kNph. Thus, for a 6-stator pole machine not only the rotor pole number can be selected as even numbers, such as 4- and 8-rotor poles, which are commonly used for SRM and DFDSM, but odd numbers, such as 5- and 7- rotor poles, are also feasible. The benefits of using 5- and 7-rotor poles are the cancellation of even-order harmonics together with the third-order harmonic in the flux-linkage and back-EMF. Hence, more sinusoidal back-EMF can be obtained to produce a lower torque ripple. The cancellation in 5- and 7-rotor pole machines is because the flux generated by field and armature windings can pass through the adjacent stator poles to form a shorter flux path, which can further increase their average torque. To validate the analysis, four prototype machines with different rotor pole numbers are manufactured and tested. [ABSTRACT FROM PUBLISHER]

This paper presents a novel method for the determination of temperature rise in rotating electrical machine. Rise in the winding temperature was determined from the estimated values of winding resistance during the heat run test conducted as per IEC standard. The estimation of hot resistance was modeled using multiple variable linear regression. The modeled hot resistance helps to find the load losses at any load situation without using complicated measurement set -up. This technique was applied for the hot resistance estimation for switched reluctance machine using the input variables as cold resistance, ambient temperature and temperature rise. The results are compared and they show a good agreement between measured and the computed values. The proposed method was verified using experimental results obtained from temperature rise test on a 2 H.P 8/6 Switched Reluctance Machine. [ABSTRACT FROM AUTHOR]

In this paper, instantaneous torque control for switched reluctance machines (SRMs) with an arbitrary number of phases is introduced. Direct portability of this control to machines with any number of phases is achieved by the developed multiphase-torque-sharing concept. This concept is also useful for SRMs where maximum torque can only be achieved by phase overlap of more than two phases. Furthermore, a new torque-sharing strategy, the low-loss-commutation strategy, for predictive pulsewidth modulation direct instantaneous torque control, is proposed that minimizes ohmic losses during commutation of two phases without the use of precomputed current or torque profiles. Additionally, no precomputed switching angles are required. They are determined online by the low-loss-commutation strategy. The strategy is especially useful for operating areas where copper losses dominate, which is usually the case at low speed. The proposed control strategies are validated by simulations and measurements on a drive test bench. [ABSTRACT FROM AUTHOR]

This paper presents a novel strategy of switched reluctance motor optimal design. The strategy is based on the so called flux linkage characteristic. The flux linkage characteristic contains most of the information of the machine and thus could be regarded as the “footprint” of the machine performance. In this work, first the desired flux linkage characteristic is identified, and then the optimal design parameters are sought after starting form this “idealized characteristic”. This could be regarded as an inverse problem. In this paper, neural networks are proposed to identify the mapping between the design variables and the flux linkage curve of the machine, and thus overcoming the nonlinearities that are inherent to this type of problems. Finite elements analysis is used to validate this approach. [ABSTRACT FROM AUTHOR]

Minimizing torque ripple in electrical machines for a given application is not a straightforward task, especially when the application imposes certain constraints. There are many techniques to improve torque ripple, either design-based or control-based. In this paper, a new geometry for switched reluctance machines based on rotor poles skewing is proposed to minimize torque ripple. This paper describes a methodology to design an asymmetrical skew rotor—switched reluctance machine using a multi-objective differential evolutionary algorithm. The main parameters of the optimization process are defined, as is the optimization methodology to obtain an improved design with less torque ripple than a conventional one. Moreover, the analytical formulas used in the optimization method, as well as the optimization technique, are deduced and explained in detail. The mathematical model used to simulate the electrical machine and the power converter are also described. Two-dimensional and three-dimensional finite element analyses were also conducted to assess whether 3D effects (end-effect and axial fringing field) affected the results. Finally, a particular case of a high-voltage direct current-controlled generator in the base of the More Electric Aircraft (MEA) concept or an energy storage system as an electrical machine was analyzed, and the results for the improved configuration were compared with those for the conventional one. [ABSTRACT FROM AUTHOR]