Search

Traditional analysis and design of induction machines have been largely based upon lumped-parameter models. An alternative tool used for field-based evaluations of an induction machine is the finite-element method. Although useful, its computational complexity limits its use as a design tool. In this paper, a field reconstruction (FR) method for induction machine simulation is introduced. The FR method utilizes a small number of finite-element evaluations to establish basis functions of normal and tangential flux densities. The basis functions are then used to estimate the magnetic field under arbitrary stator excitation. Using such a tool, evaluation of fields and forces produced by a machine under alternative excitation strategies can be explored efficiently. Moreover, alternative field-based derivation of stator/rotor excitation control can be explored. Index Terms--Field reconstruction (FR), finite element (FE), induction machine, Maxwell stress tensor, torque and radial force.

Traditional analysis of permanent magnet synchronous machines has focused upon establishing a relationship between the quadrature (q) and direct (d) axis stator current (or voltage) and the electromagnetic force created to establish rotation (torque). In this paper, an alternative analysis of electromagnetic force production is considered. Specifically, the influences of q- and d-axis stator current on both the radial and tangential components of the airgap flux densities are first evaluated. Using a Maxwell stress tensor approach, the fields are then used to evaluate both the radial and tangential component of force density created in the airgap of the machine. From this perspective several interesting observations are made. First, it is shown that the d-axis current has zero influence on the average tangential force (torque), as predicted using traditional analysis, but it has a significant influence on the average radial component of force. Second, it is shown that the q-axis current contributes to both the average radial and average tangential components of force. Interestingly, it is also shown that under standard operating conditions, the average radial force far exceeds that of the average tangential component of force. Therefore, one can conclude that the magnetic fields established create a significant component of force in a direction that cannot produce torque. Index Terms--Force density, maxwell stress tensor, permanent magnet synchronous motor (PMSM), torque generation.

Development of a precise dynamic model is a critical step in design and analysis of optimal control strategies for switched-reluctance machines (SRM). This paper is focused on important issues concerning the development of such models and their subsequent use in designing control strategies for SRM drives. The main goal in modeling is to provide a good accuracy over the entire speed and torque range. To achieve this objective, the following requirements need to be met: 1) a good accuracy in matching the inductance of each stator phase; 2) inclusion of mutual effects when significant overlap among phases exists; 3) inclusion of short flux-path operation in each electrical cycle when significant overlap among adjacent phases exists; and 4) capability for autocalibration to cope with parameter variations incurred by manufacturing imperfections and operational conditions. In this paper, in addition to an in-depth discussion of the above factors, a practical modeling approach along with an autocalibration strategy is presented. A simple test collects the necessary data in developing the proposed model. Inherent separation among mechanical, electrical, and control time constants has been used to develop the autocalibration process. Experimental results are presented to validate the proposed method. Index Terms--Long flux path, mutual inductance, self-inductance, short flux path, switched reluctance machines (SRMs).

Vibration caused by torque ripple and radial force harmonics is a concern in many applications of permanent magnet synchronous machines (PMSMs). Alternative methods of machine design and/or stator excitation to minimize torque ripple have received considerable attention in recent years. Comparatively, methods to minimize radial force harmonics have received less attention. In this paper, a field reconstruction (FR) method is derived that provides a designer with the capability to rapidly determine the radial and tangential components of force under arbitrary stator excitation. Using the field reconstruction method, stator current waveforms that minimize the ripple of both torque and radial force are derived subject to the constraint of maintaining a satisfactory level of torque density. Index Terms--Finite element analysis (FEA), force density, permanent magnet machine, torque ripple.

Fault tolerance is a critical attribute in automotive electrical and propulsion systems. In this paper, a control scheme is presented that allows an induction motor drive system to operate in the event of multiple sensor failures. Automatic diagnosis of sensor fault and recovery is performed and used to reconfigure the drive system controls to achieve the best performance in lieu of component degradation. This approach couples a new digital delta-hysteresis regulation scheme with a model reference adaptive system scheme in order to provide fault tolerance for both phase-current and rotor position (speed) sensors. Simulation and experimental results are provided to show the effectiveness of the proposed scheme. Index Terms--Current regulation, induction drives, model reference adaptive system (MRAS) speed identification, sensor fault diagnosis, sensor fault tolerance.

Switched reluctance machines (SRM) offer attractive attributes for automotive applications. These include robustness to harsh operational conditions, rugged structure, fault resilient performance, and a wide range of speed. The main debate over the adequacy of switched reluctance drives in automotive applications has often focused on efficiency and position sensorless control over the entire speed range, adaptation of control algorithms in the presence of parameter variations, and high levels of acoustic noise and vibration. The present paper demonstrates three key technologies developed over the past few years that have resulted in tangible improvements in the performance of SRM/generators (SRM/G) as related to the above areas of interest. This paper intends to illustrate the new possibilities and remaining challenges in applications of SRM in automotive industry. The proposed technologies have been validated by simulation and experimental results. Index Terms--Acoustic noice, switched reluctance machines (SRM), vibration.

Development of a reliable, smooth, and precise position sensorless startup routine is an integral part of the switched reluctance machine (SRM) control. The proposed sensorless startup method presented in this paper presents high grade performance and does not require additional hardware or memory. Further, the proposed sensorless technique is extended to rotating shaft conditions. These capabilities are highly demanded by automotive applications such as starter/alternator and electric power steering systems. An assessment of the impact of motor parameters and diagnostic signal measurement on the quality of the sensorless startup method is also included. This will help practicing engineers to make judicious selections for implementation of the proposed technique. Experimental and theoretical results are included to validate our claims. Index Terms--Diagnostic signal measurement, switched reluctance machine (SRM).

This paper presents the results of an investigation of components of the electromagnetic force in the air gap of an 8/6 switched reluctance machine (SRM). Using a Maxwell stress method, variations of radial and tangential force components due to saliency of the machine and saturation have been studied. Access to distribution of the force components acting on the rotor and stator enables us to provide a more accurate picture of the torque generation and vibration in this family of electric machines. Furthermore, distribution of magnetic forces under multiphase excitation has been studied in detail. Our findings show that bipolar excitation of SRM phases, resulting in a short flux path magnetic circuit, favors its efficiency and power quality while generating higher torque with less pulsation. This is a significant improvement, particularly for automotive applications where the difference in the required number of power electronics components can be justified. An experimental 2-kW 42-V 8/6 SRM drive which has been designed and manufactured in our energy system laboratory was targeted for this study. In addition to our extensive finite-element analysis, experimental results have been provided to prove theoretical claims. Index Terms--Bipolar, normal force, switched reluctance machine (SRM), tangential force.

Current vehicle architectures utilize belt driven components such as the coolant pump, air-conditioner, power steering pump, etc. However, the trend toward more electric vehicles requires electromechanical energy conversion devices to replace these inefficient mechanical components. It is essential that electrical machines used in automotive applications to be compatible with the corresponding mechanical and electrical terminals. Furthermore, replacement of belt driven components with electrical drives should be performed as efficient and cost effective as possible. Bipolar switched reluctance machines (SRM) are both cost effective and very robust to the effects of temperature variation. They also offer a very wide speed range and an excellent mechanical integrity, which optimally suits a range of automotive applications including electric propulsion. This paper presents a detailed investigation of the performance indices for bipolar SRM drives. Using a Maxwell stress method, variations of radial and tangential force components due to saliency of the machine and saturation have been studied. Access to distribution of the force components acting on the rotor and stator enables us to provide a more accurate picture of the torque generation and vibration in this family of electric machines. Furthermore, distribution of magnetic forces under multiphase excitation has been studied in detail. Our findings show that bipolar excitation of SRM phases, resulting in a short flux path magnetic circuit, favors its efficiency and power quality while generating higher torque with less pulsation. This is a significant improvement, particularly for automotive applications where the difference in the required number of power electronics components can be justified. An experimental, 2-kW, 42-V, 8/6 SRM drive which has been designed and manufactured in our energy system laboratory was targeted for this study. In addition to our extensive finite-element (FE) analysis, experimental results have been provided to prove theoretical claims. Index Terms--Bipolar, normal force, switched reluctance machines (SRM), tangential force.

Proper synchronization of the excitation with respect to the rotor position is essential in optimal control of switched reluctance motor (SRM) drives. To avoid additional cost, size, and unreliability caused by the external position sensors, magnetic status of the SRM can be directly monitored to detect commutation instants. A one-to-one correspondence between magnetic status of the SRM and rotor position removes the need for an explicit access to the rotor position. In order to obtain a good precision over the entire speed range, educated modifications on the structure of the sensorless strategy is necessary. This is due to the impact of the operational regions on dynamic behavior of the SRM. In addition, introduction of SRM technology to industrial and domestic applications has raised the need for four-quadrant operation of the SRM drives. The present paper introduces a range of strategies that are necessary to accommodate this requirement in a sensorless format. Our experimental findings indicate that high-grade sensorless operation in a four-quadrant SRM drive is possible and can be integrated in a variety of applications. Index Terms--Rotor position, switched reluctance motor (SRM) drives.

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. Index Terms--Flux linkage, incremental inductance, magnetic saliency, model identification.

This paper covers the range of topics related to sensorless control of switched reluctance motor (SRM) drives from their fundamentals to their limitations and state of the art and future trends. This should help the reader to develop a systematic understanding of the sensorless techniques that have been developed over the past two decades. The inherent vulnerability to mechanical failures, extra cost, and size associated with external position sensors such as optical encoders, resolvers, and custom-designed Hall-effect sensors has motivated many researchers to develop sensorless control techniques for SRM drives. Ideally, it is desirable to have a sensorless scheme, which uses only terminal measurements and does not require additional hardware or memory while maintaining a reliable operation over the entire speed and torque range with high resolution and accuracy. Recent advances in the development of low-cost digital-signal-processor-based microcontrollers have paved the way for the fulfillment of this objective. It is, furthermore, our view that the existing trends in the development of more powerful processors will ultimately replace the concept of sensorless controls with the concept of eliminating the need for position sensing, a concept that will further revolutionize the motor drive technology. Index Terms--Adjustable-speed motor drives, motor controls, motor drives, reluctance motors, sensorless controls, switched reluctance motors, variable reluctance motors.