Analysis and characterization of switched reluctance motors: Part I /sub y/namic, static, and frequency spectrum analyses

This paper consists of three parts. Section I explores two software applications for modeling and simulating the dynamic characteristics of switched reluctance motors (SRMs). The software applications are the electromechanical structure system (EMSS), which is a tool within the proprietary Maxwell SPICE environment, and power system computer-aided design (PSCAD). The major parameter of an SRM, the nonlinear winding inductance, which determines the dynamic torque, is individually modeled for use with these applications. Simulation of the dynamic torque and the speed for any load is discussed. Section II presents a new stator geometry for SRMs that improves the torque profile. In the new geometry, pole shoes are affixed to the stator poles. The paper discusses a sensitivity study of the torque profile using a two-dimensional finite-element field simulation. Section III presents a frequency spectrum analysis of torque profile using the fast Fourier transform (FFT) capability of MATLAB. Salient features of this analysis for torque profile of SRM and the results of simulation are presented. Section IV concludes the paper.     

An Analytical Circuit Model of Switched Reluctance Motors

We have developed a dynamic analytical circuit model to simulate the performance of switched reluctance motors (SRMs). Our model expresses flux linkages as multiple decoupled one-argument functions, either current dependent or rotor position dependent, instead of one two-argument function dependent on both current and rotor position. We propose a novel approach for the computation of the air gap permeance at various rotor positions. By using this analytical model, the performance of a SRM can be simulated very efficiently and with improved accuracy. As an application example, we present a simulation of an 8/6 pole SRM in the system domain, and compare the results with transient finite element analysis (FEA) solutions.      

A novel switched reluctance motor with C-core stators

This paper presents a novel switched reluctance motor (SRM) design in which the stator is simply formed from C-cores. Unlike conventional SRMs, the windings of the new motor can be individually wound into the stator cores without complex winding equipment. Because of the inherent axial field distribution, this type of SRM requires a three-dimensional (3-D) finite-element analysis (FEA) model for detailed flux analysis. This paper proposes an approximated two-dimensional FEA model to speed up computational time. In addition, since the proper current that ensures operation in the saturated region (to maximize torque and efficiency) is often hard to determine systemically, the paper proposes a simple method to determine the optimum operating current so that one can easily decide the rated current and also obtain the maximum motor efficiency. Finally, the paper compares some characteristics of a traditional SRM with those of the proposed SRM. The comparison shows that the proposed SRM performs well in terms of torque and efficiency, and provides a higher degree of flexibility in winding design.     

An improved method for the determination of saturationcharacteristics of switched reluctance motors

Experimental determination of magnetization characteristics of switched reluctance motors (SRMs) is quite important in their accurate performance prediction. Over the last decade, various experimental procedures have been used to obtain these characteristics. Every evolved new method has its own limitations and constraints. This paper describes an improved, simple and cost effective experimental procedure and an equally simple post-experimental data processing to obtain the flux-linkage-current curves at varying rotor positions of the SRM. The experimental results on a 4 kW, four-phase, 8/6 pole SRMs show the effectiveness of the method and the results compare well with the previously results compare well with the previously published results of similar and higher rating SRM's     

Improvement in the field-weakening performance of switched reluctance machine with continuous mode

A new operation mode for switched reluctance motors (SRMs), called 'continuous mode', is described. By using this mode, the torque and then power in field-weakening mode can be considerably increased without any hardware modifications. Consequently, power and torque densities of SRMs become comparable to other technologies (synchronous and induction motors) and with a field weakening operation over a large speed range. This new degree of freedom makes it possible to improve the motor design, by modifying the rotor pole arc size or the windings turns per pole. Only simulation results are presented here, for a 12/8 SRM. Results confirm that the maximum power is improved (constant power on a very large speed range) and with a higher efficiency than that in the classical discontinuous mode.     

Fast Calculation of Field Currents and Reactances for Doubly Fed Generators With Rotor Duct Pieces

Doubly fed generators have been used as adjustable-speed pumped-storage generator motors and wind turbine generators. Accurate determination of field currents and reactances is important for the design of these machines. We propose a calculation method to obtain the field currents and reactances of machines with rotor duct pieces under any steady-state balanced load condition. The method links two-dimensional static finite-element analysis (FEA) with an approximate calculation to consider three-dimensional (3-D) skin effect in the duct pieces. Its advantage is that the computational time is much smaller than 3-D transient FEA when the slip frequency is not zero. The method will contribute to improvement of the design of doubly fed generators with rotor duct pieces. It was applied to a 395 MVA machine, and the calculated field currents agreed well with the measurements. Variation in the reactances due to saturation is also discussed     

Temperature Rise Analysis of Switched Reluctance Motors Due to Electromagnetic Losses

We present a finite-element analysis of the temperature rise of switched reluctance motors (SRM) due to electromagnetic losses. We estimate the various components of electromagnetic losses, including core loss in the lamination as well as copper and eddy-current losses in windings, and then predict the temperature rise within the motor due to these losses. We present simulation results for an 8/6 SRM and discuss various aspects of thermal design of SRMs. To validate the procedure for the estimation of electromagnetic losses, we compare predicted and measured losses.      

Three-dimensional resistance calculation in end ring of inductionmotor by finite-element method

Among the components of induction motors, the end ring is needed to connect rotor bars electrically. Some approaches to calculating its resistance employ equivalent circuit methods, but they are not accurate because they assume ideal sinusoidal current distribution. This paper presents a method to calculate the current distribution in the end ring by the finite-element method (FEM). This paper uses both two-dimensional (2-D) A-Φ FEM analysis and three-dimensional (3-D) T-Ω FEM analysis. The magnetic flux density is obtained from 2-D analysis, and the electric vector potential is obtained from 3-D analysis. With these results, the current distribution in the end ring is calculated and the proper size of the end ring is selected by solving some case problems     

Diagnosis of Static Eccentricity in Switched Reluctance Motors Based on Mutually Induced Voltages

This paper presents a novel method for diagnosis of eccentricity in a switched reluctance motor (SRM). The method employs two-dimensional finite-element analysis to calculate mutual fluxes and mutually induced voltages in an 8/6 SRM. An investigation of the effect of static eccentricity on these quantities shows that eccentricity has a considerable effect on them. Since flux measurement is costly, the method introduces mutual voltage as a suitable criterion for diagnosis of eccentricity in SRMs.      

复合分子泵转子离心变形与热变形的有限元分析

本文利用有限元分析软件ANSYS12.0对复合分子泵转子的离心变形与热变形进行了分析。通过施加惯性载荷和温度载荷,得到转子的离心变形与热变形。对不同载荷下分析结果的比较,了解了惯性载荷与温度载荷对分子泵转子变形影响大小。通过分析结果可直观了解分子泵在高速运转过程中转子变形情况,对分子泵设计时工作间隙的选取有重要的参考意义。     

A three-dimensional field solution for permanent-magnet axial-fieldmotors

A formula is presented for computing the field in axial-field permanent-magnet motors. The formula is based on a three-dimensional (3-D) analytical analysis and is expressed in terms of a finite sum of elementary functions. It is readily programmed and ideal for parametric studies of field strength. It is also well suited for parallel processing and could be developed into a motor model for real-time performance simulations. It is applied here to a practical motor geometry and verified by the use of 3-D finite element analysis (FEA)     

Analysis of magnetic field and levitation force characteristics for 3-DOF deflection type PM motors

The mechanism and characteristics of the electromagnetic radial force are important for motors with complicated structures. The three-dimensional analytical model of the air gap between the rotor and stator is established under rotor eccentricity conditions. Then, aiming at solving the unbalanced radial force problem with rotor static eccentricity, the air-gap flux density, radial electromagnetic force, and the comparisons of harmonic contents are calculated and presented based on FEA (Finite Element Analysis) and MATLAB simulation. Finally, the magnetic field model has been validated by experiments utilizing a prototype system. The results provide a theoretical guide for configuration design, optimization, and levitation control research on three degree of freedom deflection type motors.     

Real-Time Verification of AI Based Rotor Position Estimation Techniques for a 6/4 Pole Switched Reluctance Motor Drive

This paper presents real-time verification of an artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) based rotor position estimation techniques for a 6/4 pole switched reluctance motor (SRM) drive system. The techniques estimate rotor position by measuring the three-phase voltages and currents and using magnetic characteristics of the SRM, with the aid of an ANN and ANFIS, in real-time environments. The rotor position estimating techniques are used in a high-performance sensorless variable speed SRM drive. A digital signal processor, TMS320F2812, executes the rotor position estimation. To verify the performance of the ANN and ANFIS based rotor position estimation techniques, a rotor position sensor is mounted with the drive system. The experimental results show that the ANN and ANFIS based rotor position estimation techniques provide good performance at different operating conditions.     

A unit cell approach of finite element calculation of ballistic impact damage of 3-D orthogonal woven composite

This paper presents ballistic impact damages of 3-D orthogonal woven composite in finite element analysis (FEA) and experimental. A unit-cell model of the 3-D woven composite was developed to define the material behavior and failure evolution. A user-defined subroutine VUAMT was compiled and connected with commercial available FEA code ABAQUS/Explicit to calculate the ballistic penetration. Ballistic impact tests were conducted to investigate impact damage of 3-D kevlar/glass hybrid woven composite. Residual velocities of conically-cylindrical steel projectiles (Type 56 in China Military Standard) and impact damage of the composite targets after ballistic perforation were compared both in theoretical and experimental. The reasonable agreements between FEA results and experimental results prove the validity of the unit-cell model in ballistic limit prediction of the 3-D woven composite. We believe such an effort could be extended to bulletproof armor design with the 3-D woven composite.     

Modeling switched-reluctance Machines by decomposition of double magnetic saliencies

This paper presents a novel analytical model for a switched-reluctance machine (SRM) based on decomposition of its inherent double joint magnetic saliencies due to rotor and stator salient poles and saturation of magnetic field at high stator currents. With this method, the magnetic characteristics of the motor, such as flux linkage and incremental inductance, are decomposed to vector functions of rotor position and phase current. Dynamic state and torque equations for the SRM are derived on the basis of this representation. The proposed model is appropriate for online identification and for sensorless position control algorithms. It is easy to implement and computationally efficient. Comparison of the predicted motor magnetic characteristics to machine data from finite-element analysis verifies the accuracy of the model.     

DSP-Based Automated Error-Reducing Flux-Linkage-Measurement Method for Switched Reluctance Motors

The switched reluctance motor (SRM) has received considerable attention from researchers for its many inherent advantages, and thus, it has become a popular research topic in the field of variable-speed drives as well as servo drives. Research on SRMs mainly includes their design, modeling and performance analysis, control, as well as applications. However, for verification of design, performance prediction, as well as development of a high-performance sensorless control algorithm, accurate measurement of the magnetic characteristics of the SRM is most critical. Hence, one of the most important problems in the field of SRMs is a practical and accurate instrumentation system for the measurement of the SRM magnetic characteristics. This paper first describes an accurate and fully automated digital method for the measurement of the magnetic characteristic of SRMs, which includes online offset-error removal and winding resistance estimation. In this method, a digital-signal-processor-based virtual instrumentation for measurement of flux linkage is developed. Then, the results of the measurement conducted on a four-phase SRM are presented. The accuracy of the measurement system is verified by comparing with that found via a magnetic analyzer. Finally, the various sources of errors and their contributions to the errors are discussed. The scheme can also be used, in general, for transformers or inductors.     

Preparation of Reference Material 8504, Transformer Oil

A new reference material (RM), RM 8504, has been prepared for use as a diluent oil with Aroclors in transformer oil Standard Reference Materials (SRMs) 3075 to 3080 and SRM 3090 when developing and validating methods for the determination of polychlorinated biphenyls (PCBs) as Aroclors in transformer oil or similar matrices. SRMs 3075-3080 and SRM 3090 consist of individual Aroclors in the same transformer oil that was used to prepare RM 8504. A unit of RM 8504 consists of one bottle containing approximately 100 mL of transformer oil. No additional constituents have been added to the oil.     

Finite element analysis of a deformable array transducer

Deformable array transducers have previously been described to implement 2-D phase aberration correction of near-field aberrators with only a 1xN or 2xN array configuration. This transducer design combines mechanical phase correction using an actuator with electronic phase correction for a 2-D correction with significantly fewer elements than a full 2-D array. We have previously reported the fabrication and results of a 1x32 deformable array fabricated with a RAINBOW (Reduced And INternally Biased Wafer) actuator. Because of the complicated construction of deformable arrays, we propose to use finite element analysis (FEA) as a design tool for array development. In this paper, we use 2-D and 3-D FEA to model the experimental results of the deformable array as the first step toward development of a design tool. Because the deformable array combines a mechanical actuator with a medical ultrasound transducer, improvement in performance must consider both the ultrasound characterization along with the low frequency actuator characterization. For the ultrasound characterization, time domain FEA simulations of electrical vector impedance accurately predicted the measurements of single array elements. Additionally, simulations of pulse-echo sensitivity and bandwidth were also well matched to measurements. For the low frequency actuator characterization, time domain simulation of the low frequency vector impedance accurately predicted measurement and confirmed the fundamental flexure resonance of the cantilever configuration at 1.3 kHz. Frequency domain FEA included thermal processing effects and predicted actuator curvature arising during fabrication. Finally, frequency domain FEA simulations of voltage-induced displacement accurately predicted measured displacement.     

Mathematical rotordynamic model for lateral vibration analysis of induction motors with dynamic eccentricities regarding start-up

The paper shows a mathematical rotordynamic model for lateral vibration analysis of induction motors with dynamic eccentricities regarding start-up. With this mathematical model, different kinds of dynamic eccentricities—mass eccentricity, magnetic eccentricity and bent rotor deflection—can be analyzed. Beside the mechanical influences—e.g. the rotor mass, rotor shaft stiffness, oil film coefficients of the sleeve bearings, structural stiffness of the sleeve bearing housings and end shields—also electromagnetic influence—e.g. the electromagnetic field and magnetic eccentricity—can be analyzed for the start-up. The paper is based on the well-known theory of accelerated resonance passing and is an enhancement of the theory for induction motors, considering also electromagnetism during start-up. Based on this rotordynamic model, the absolute displacements of the shaft centre, the shaft journals and the sleeve bearing housings can be analyzed as well as the relative displacements between the shaft journals and the sleeve bearing housings. Additionally, also the vibration velocities at the sleeve bearing housings can be derived. The aim of the paper is not to replace a detailed finite-element-model by a simplified analytical model, but to show the mathematical coherences between rotordyamics and electromagnetics for a start-up of an induction motor, considering different dynamic eccentricities.