A simple model for switched reluctance motors

This letter presents a simple model of nonlinear magnetization characteristics of a switched reluctance motor (SRM). The flux linkage is given as a continuous function of phase current and rotor position. This allows a mathematical formula to be found for the instantaneous torque. The model is valuable for computer-aided designs, especially for sizing and initial estimates where accuracy can be traded with time saving. The model was implemented to verify its degree of accuracy. The simulation program has the ability to calculate numerous parameters that can be very useful for quick estimates of the efficiency of a particular SRM drive or for motor selection     

Conducting screen utilisation in switched reluctance motors

In this paper, the effect of incorporating nonmagnetic electrical conducting screens in the motor topology of a switched reluctance motor is investigated. It is shown that screens on the rotor increase the motor torque by reducing the effective unaligned AC inductance due to the eddy currents induced in the screens. Screens added to the end laminations on both the rotor and stator stacks are shown to minimise the end flux leakage. Details of experimental and analytical methods used to evaluate the effects of conducting screens are provided and test results on a 500 W motor are included     

Aspects of design optimisation for switched reluctance motors

Existing papers about suitable switched reluctance motor (SRM) airgap dimensions, which give optimum performance for doubly-salient structure motors, are reviewed and their deficiencies are mentioned. The recommendations of these papers cover a wide range of t/λ (tooth width/tooth pitch), which can optimise the performance of the SRM. Although some parts of these results are supported by the present work, some other parts may not be correct. A developed software package has been applied to the design of a single-tooth peg stator pole SRM. It is concluded that the optimum ratio of t/λ is between 0.33 and 0.40. Using the design constraints considered, the optimum split ratios (defined as the ratio of rotor diameter to stator outer core diameter) are estimated at between 0.57 and 0.63. The ratio between the back of core width and half of tooth width in the motor is estimated and it is found that the best range of this ratio is from 1.1 to 1.3     

Resonant frequencies and mode shapes of switched reluctance motors

The wide application of switched reluctance motors (SRM) is limited by their higher vibration and acoustic noise. An accurate determination of resonant frequencies and mode shapes of the SRM stator is therefore essential for low acoustic noise design. Based on the structural finite element method and elasticity theory, 3D vibration modes and resonant frequencies of a 5 HP SRM with 8/6 poles are demonstrated and calculated in this paper The stator stack with both a smooth frame and a ribbed frame are examined. The effects of an encased frame and a keyed frame on the free vibration modes and resonant frequencies of SRM stator are compared. Accelerometer test results on a SRM verify some of the numerical computations     

Iterative learning-based high-performance current controller for switched reluctance motors

Switched reluctance motors (SRMs) are being considered for variable speed drive applications due to their simple construction and fault-tolerant power-electronic converter configuration. However, inherent torque ripple and the consequent vibration and acoustic noise act against their cause. Most researchers have proposed a cascaded torque control structure for its well-known advantages. In a cascaded control structure, accurate torque control requires accurate current tracking by the inner current controller. As SRM operates in magnetic saturation, the system is highly nonlinear from the control point of view. Developing an accurate current tracking controller for such a nonlinear system is a big challenge. Additionally, the controller should be robust to model inaccuracy, as SRM modeling is very tedious and prone to error. In this paper, we have reviewed various current controllers reported in the literature and discussed their merits and demerits. Subsequently, we have proposed and implemented a novel high-performance current controller based on iterative learning, which shows improved current tracking without the need for an accurate model. Experimental results provided for a 1-hp, 8/6-pole SRM, demonstrate the effectiveness of our proposed scheme.     

Low torque ripple control of switched reluctance motors usingiterative learning

Torque control of the switched reluctance motor is complicated by its highly nonlinear torque-current-position characteristics. The purpose of this paper is the development of simple and efficient control algorithms for the constant torque control of switched reluctance motors. The approach consists of two distinct steps, i.e., determination of appropriate phase current waveforms for some specified torque and the subsequent generation of suitable phase voltage profiles for faithful tracking of these waveforms by the respective stator windings of the motor. At both the stages of the control design, the principles of iterative learning control have been exploited. Firstly, the desired current waveform is generated by repeated corrections from iteration to iteration starting from the conventional rectangular current profile as the initial waveform. This scheme requires much less a priori knowledge of the magnetic characteristics of the motor. In the second stage, the voltage profiles to be impressed upon the stator phases for the tracking of the desired current waveforms are learnt iteratively. Simulation results show impressive response characteristics for four-phase switched reluctance motor     

Preliminary performance evaluation of switched reluctance motors with segmental rotors

This paper examines the performance of switched reluctance machines which employ a segmental rotor construction in preference to the usual toothed structure. Two three-phase designs are considered, one in which the windings span a number of teeth and one in which they span a single tooth. Two demonstrators have been built-one for each design type, and their performances are compared with both conventional switched reluctance motors (SRMs) and a rare earth permanent-magnet machine. It is shown how these machines can operate from a standard SRM converter: running test results are presented and there is a discussion of general operating experience, ranging from the measurement of mean torque, voltage, and current-controlled operation to general thermal performance.     

Neural network-based modeling and parameter identification of switched reluctance motors

Phase windings of switched reluctance machines are modeled by a nonlinear inductance and a resistance that can be estimated from standstill test data. During online operation, the model structures and parameters of SRMs may differ from the standstill ones because of saturation and losses, especially at high current. To model this effect, a damper winding is added into the model structure. This paper proposes an application of artificial neural network to identify the nonlinear model of SRMs from operating data. A two-layer recurrent neural network has been adopted here to estimate the damper currents from phase voltage, phase current, rotor position, and rotor speed. Then, the damper parameters can be identified using maximum likelihood estimation techniques. Finally, the new model and parameters are validated from operating data.     

Starting of three-phase reluctance motors connected to a singlephase supply

An analysis of the starting process of a three-phase reluctance motor when fed from a single-phase supply is presented. This analysis is aimed, mainly, at the determination of the variations in the different machine parameters as it pulls into synchronism. Special attention is given to the calculation of both the positive and negative sequence impedances. These impedances play an important role in the proper selection of the phase converter capacitance needed for ensuring satisfactory operation. For this purpose, the symmetrical component concept along with classical synchronous machine theory have been effectively employed. The devised mathematical model could also help in studying the asynchronous operation of synchronous machines when fed from either three-phase or single-phase power supplies. The effect of the value of the selected phase converter capacitance on the performance of the reluctance motor during starting and normal running conditions is investigated     

Starting transients of three phase reluctance motors as affected bytorsional dynamics

In this paper, a rigorous mathematical model describing the transient behavior of three-phase reluctance motors under the effect of torsional dynamics is developed. Provisions are made to allow the analysis of both the three-phase balanced mode of operation and the single-phase mode of operation of such motors. The resulting state-space equations are then solved numerically in order to yield the required transient response curves. The outcome of this study will help in devising techniques to deal with the dangerous consequences of the electromechanical resonance phenomenon that may arise     

Comparison of the nature of torque production in reluctance andinduction motors

The nature of torque production is different in reluctance and inductance motors. One significant difference occurs in a reluctance motor that has nonsalient stator punching and a salient motor. When the flux per pole is small in such a motor, the torque can still be high, as long as the rate of energy change with respect to the rotor angular displacement at the rotor pole fronts and pole ends is high. A theoretical foundation to improve the torque capability of reluctance motors is provided. Effects of saturation and stray-load loss are also studied. Experimental results show agreement with theoretical conclusions     

On the use of a simplified model for switched reluctance motors

The paper presents a simple model for the nonlinear magnetization characteristics of a switched reluctance motor (SRM). The flux linkage is given as a continuous mathematical expression, depending on the phase current and rotor position. This expression can then be differentiated or integrated easily without computer use; it enables finding a mathematical formula for the instantaneous torque of each phase. The model is valuable for computer-aided designs, especially for sizing and initial estimates, where accuracy can be traded with time saving. The model was implemented to verify its degree of accuracy. The simulation program has the ability to calculate numerous parameters that can be very useful for quick estimates of the efficiency for a particular SRM drive or even when choosing a particular motor.     

A methodology for characterizing fault tolerant switched reluctance motors using neurogenetically derived models

This paper examines the feasibility of using artificial neural networks (ANNs) and genetic algorithms (GAs) to develop discrete time dynamic models for fault free and faulted switched-reluctance-motor (SRM) drive systems. The results of using the ANN-GA-based (neurogenetic) model to predict the performance characteristics of a prototype SRM drive motor under normal and abnormal operating conditions are presented and verified by comparison to test data.     

Steady-state performance of reluctance motors under combinedfundamental and third-harmonic excitation. II. Experimental results

Experimental results for two prototype, grooved and segmental type, reluctance motors under combined fundamental and third-harmonic excitation are presented. Test data are used to verify the theoretical models. The agreement between theoretical and experimental values is very good. Experimental data show the torque capability increase made possible by the injected third-harmonic MMF interacting with the third space harmonic flux resulting from the interaction between the fundamental MMF and the rotor is 10% for a grooved-type reluctance motor operating in the saturated region. For a segmental-type reluctance motor, the capability increase is 20%, even when the motor is still operating in the nonsaturated region     

Mathematical and experimental method to obtain the inverse modeling of nonsinusoidal and saturated synchronous reluctance motors

This paper presents new inverse modeling for synchronous reluctance motor (SyRM). This modeling is valid when the inductances are sinusoidal or nonsinusoidal and even when the machine is saturated. This technique involves the generation of constant torque curves as a function of two-phase currents in the Concordia's reference frame when the rotor angle is fixed. We also introduce an experimental method to obtain directly the inverse modeling. This practical method takes into account the saturation of the motor. This technique allows the reduction of the low torque ripple in the case of nonsinusoidal inductances.     

Off-line testing of reluctance machines

Experimental techniques for determining the machine parameters and results demonstrating their performance on an axially-laminated synchronous reluctance motor are presented. A new software implementation of the control algorithm for conducting an instantaneous flux-linkage test is developed. A low frequency AC test allowing better estimation accuracy compared to a standard 50-Hz test is proposed. Effects of stator slotting on the quality of DC torque test estimates are examined     

A novel multilayer switched reluctance motor

The switched reluctance motor is a simple and robust machine, which has found application over wide power and speed ranges in different shapes and geometries. This paper introduces a new configuration for a high starting torque switched reluctance motor (SRM). This configuration allows more space for coil windings in small size motors with a high number of stator and rotor poles. It also presents a centrifugal switch mounted on the motor shaft for a sudden advancement of current-pulses relative to rotor position after reaching a preset motor speed in order to develop higher torque at starting. To evaluate the motor performance, two types of analysis, namely numerical techniques and an experimental study have been utilized. In the numerical analysis, due to the highly nonlinear nature of the motor, a finite element analysis is employed, and for the experimental study, a prototype motor has been built and tested. Finally, the prototype motor is compared with a conventional SRM of the same size. The calculated results compare favorably with the test results. In comparison with the conventional SRM, the proposed motor in this paper seems to be very promising     

Rotor design optimization of synchronous reluctance machine

It is demonstrated that the rotor design of synchronous reluctance machines can be optimized in terms of a key geometric parameter, i.e., the ratio of the rotor insulation width to the rotor iron width so as to obtain maximum torque production. The equation which gives the maximum motor power factor in terms of the saliency ratio has been derived and it is shown that the power factor of 0.8 is a realizable value with the optimal rotor design. An experimental motor has been fabricated and the results of measurements of the motor parameters prove the validity of the rotor design optimization     

Synchronous operation of a dual-winding reluctance generator

This paper sets forth the analysis and performance characterization of the dual-winding reluctance machine fed with direct current control winding excitation operating as a generator. Saturation effect, core and harmonic losses are included in the dynamic and steady state models of the generator feeding either an impedance or a rectifier load which give calculation results that compare favorably with the experiment