The switched reluctance motor has the advantages of the low production cost, high operating efficiency, high stability, and high start torque. It can deliver a wide speed range, and therefore make it very attractive to the engineers and researchers. The double salient structure of SRM result in a non-linear stator inductance, so the output reluctance torque has a highly non-linear behavior. A digital signal processor based drive system for SRM is developed and implemented in this thesis using the TI TMS320F240 DSP system which is with universal peripheral interface circuits. The built-in pulse width modulation(PWM) module of the DSP system can auto-generate PWM output signal by setting the relative registers to simplify the hardware design. This research built a complete drive system for SRM, both the closed-loop velocity controller and current compensator were designed according to the proportional-integral(PI) control mechanism, and all schemes were coded in the DSP program. Simulation and experiment results demonstrate that the proposed drive system makes reluctance torque output very smoothly with a preferable velocity response.

This research focuses on the creation of a thermal estimator to be used in an integrated electromagnetic, thermo-mechanical design tool for the rapid optimal initial sizing of switched reluctance and induction machines. The switched reluctance model includes heat generation in the rotor due to core losses, heat transfer across the air gap through convection, and a heat transfer path through the shaft to ambient. Empirical Nusselt correlations for laminar shear flow, laminar flow with vortices and turbulent flow are used to estimate the convective heat transfer coefficient in the air gap. The induction model adds ohmic heat generation within the rotor bars of the machine as an additional rotor heat source. A parametric, self-segmenting mesh generation tool was created to capture the complex rotor geometries found within switched reluctance or induction machines. Modeling the rotor slot geometries in the R-θ polar coordinate system proved to be a key challenge in the work. Segmentation algorithms were established to model standard slot geometries including radial, rectangular (parallel-sided), circular and kite-shaped features in the polar coordinate system used in the R-θ solution plane. The center-node mesh generation tool was able optimize the size and number of nodes to accurately capture the cross sectional area of the feature, in the solution plane. The algorithms pursue a tradeoff between computational accuracy and computational speed by adopting a hybrid approach to estimate three dimensional effects. A thermal circuits approach links the R-θ finite difference solution to the three dimensional boundary conditions. The thermal estimator was able to accurately capture the temperature distribution in switched reluctance and induction machines as verified with experimental results.

This thesis intends to examine the principles of operation for switched reluctance machines (SRM) and examine the power electronic drive circuits that control them, in order provide a basis of understanding for evaluating total drive efficiency and responsiveness potential. This document specifically examines the characteristics of a motor drive circuit which affect motor and converter efficiency and driving performance. A drive topology suited for efficient operation and excellent responsiveness is proposed. Finally, a SRM drive system model for evaluating these systems in simulation is described as a tool for comparative evaluations in future work. The end goal of this work is to provide a foundation of knowledge for future work, developing in-wheel, SRM-based, high performance hybrid electric drivetrains in future ground combat vehicles which are modular, possess an open architecture for upgrades, and operate with high efficiency and improved mobility. / text

This thesis presents the development of an in-wheel drive system consisting of an axial-flux switched-reluctance motor and a hub suspension. The motor is designed using Maxwell's stress tensor and numerical analysis techniques, including FEA and transient numerical simulations. A new integral inductance function is introduced that improves the accuracy of the motor model, and a new in-phase current-shaping technique is implemented using a fuzzy controller to extend the constant-power region of the motor. The hub suspension system is simulated using a half-car model with 6 degrees of freedom, and the overall torque, power, and efficiency of the drive system is calculated. A peak torque of 500[Nm] is developed at the high end of the drive system's speed range, and the hub suspension system is shown to eliminate the impact of the motor's increased unsprung mass on vehicle handling.

With the increasing environmental impact from the automotive industry, electric vehicles become more and more popular. This combined with the great breakthroughs in fast electronics the switched reluctance motor (SRM) has again gained popularity in recent years. Due to its cheap and rugged construction it is a good alternative to the permanent magnet motors and to the induction motor. The ́two main problems holding the SRM back are torque ripple and the acoustic noise generated from it. A lot of research is currently being performed in order to find a solution to these issues. This thesis has investigated different materials for the rotor in a high speed SRM. Different materials have been evaluated based on both mechanical and magnetic properties. This is done through simulations of the forces acting on the rotor combined with simulations of the magnetic field. The forces are simulate in the DASSULT SYSTEMS ABAQUS program and the magnetic field is simulate using AVL FIRE. Three different kinds of alloys are investigated, two different cobalt alloys are simulated as well as a silicon alloy with pure iron as a reference. The results show that the material needs to have a yield strength of at least 349 MPa to withstand the forces affecting the rotor. And that by using the high purity cobalt-iron alloy the generated torque could be increased with up to 20.9%, but with a cost increase of 3151.9% compared to the silicon alloy.

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This thesis presents advanced torque control methods for torque ripple reduction and performance improvement in switched reluctance motor (SRM) drives. A new offline torque sharing function (TSF) method is proposed for torque ripple reduction in SRMs. The proposed TSF achieves lower current tracking error by establishing a new current reference generation strategy. The phase current reference is first derived from the torque command using offline calculations and also from the phase current response that is obtained from the dynamic model of the SRM. Then, an optimization problem is formulated to shape the current reference for the objective of minimizing the torque ripple and copper losses, while maintaining the required average output torque at the given operating speed. The dynamic simulation of the SRM model is also utilized in the optimization problem. A new online TSF method is proposed for torque ripple reduction in SRMs. The proposed TSF takes the current dynamics and induced electromotive force into account by establishing a new online current profile generation technique. First, a primary phase current reference derived from the torque reference is applied to the SRM. Then, the decaying phase current after the turn-off angle is sampled, and it is used to update the current reference. A new online optimization strategy is performed to shape the current reference during the operation of the machine. Owing to the proposed current profile generation technique, the optimization process is decoupled to independently minimize the torque ripple by optimizing the turn-on angle and minimizing copper losses by optimizing the turn-off angle. Compared to the conventional TSFs and existing optimization-based TSFs, the proposed two TSFs achieve accurate torque control, improved torque-speed capability, reduced torque ripple, and better current tracking performance. All the proposed TSF methods are validated by both simulations and experiments on a 3-phase, 12/8 SRM. / Dissertation / Doctor of Philosophy (PhD)

This thesis presents a torque control mechanism for switched reluctance machine (SRM) drives. The proposed mechanism is capable of maintaining ripple free torque control while minimizing the copper loss or mode-0 radial force or both at a fixed switching frequency. In the proposed approach, the torque control problem is addressed by splitting it into two parts. The first part consists of identification of optimum phase current references while the second part incorporates the design of an efficient current controller. For the identification of optimum phase current references, three algorithms are presented in the form of a developmental process. The nature of the online optimization problem is demonstrated using a simple 2-dimensional gradient descent method. Subsequently, a parametric form gradient descent algorithm is presented which transforms the original optimization problem into two 1-dimensional problems, viz. torque error minimization and identification of optimum search direction. This method yields improved computational efficiency and accuracy. The third algorithm incorporates projection using equality constraint on the phase torque contributions to achieve a 1-dimensional solution process. Although this algorithm takes more iteration as compared to the parametric form gradient descent algorithm, it demonstrates greater accuracy and computational efficiency. A comparative analysis of these algorithms is performed in at different operating conditions in terms of the torque ripple magnitude and computational effort. The thesis also presents a comprehensive analysis of well known control techniques for application in SRM current control in discrete-time domain. This analysis also presents a comparative evaluation of these control techniques under different operating conditions. On account of this analysis, several recommendations pertaining to the performance improvement are presented. Finally, a digital sliding-mode based model-free current controller suitable for fixed switching frequency operation is presented. The proposed controller is capable of providing a consistent dynamic response over wide operating range without utilizing any model information. The reference current tracking performance of this controller is verified through simulation studies in MATLAB/Simulink® environment and over a 1.2kW, 100V, 2500RPM, 12/8 experimental SRM drive. / Thesis / Doctor of Philosophy (PhD)

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Switched reluctance machines (SRMs) are gaining increasing interest in industrial applications due to their low manufacturing cost, simple and robust structure, excellent fault-tolerant capability, and reliable operation in high-temperature operating environments. However, the inherent pulsative torque and radial force lead to the well-known torque ripples and acoustic noise issues. Although there are numerous advanced methods to address the above two issues, the high nonlinearity inevitably brings difficulties in controlling the SRMs. Since the linear SRM voltage and toque equations are simple, it would be beneficial to explore the control algorithm by using such simple linear model. The application of the linear torque model is firstly explored. To utilize such simple model, the connections between the linear toque model and the nonlinear torque model are built through the mapping. The features of these mapping curves are studied in detail. Applying the linear torque equation to generate the reference currents in the optimization-based torque sharing function method shows a significant reduction of the time consumption in solving the bi-optimization problem. Later, the complete equivalent linear SRM model is constructed by introducing the linear voltage equation and corresponding mapping. Since the linear model is easy to predict the behaviour of SRMs, it is beneficial to apply such model in the model predictive torque control (MPTC) methods. The application of the equivalent linear model in the finite control set (FCS) MPTC method shows a low computational burden and occupies less storage space. Besides, the improved switching table in the proposed FCS MPTC method also enhances the torque control performance in high-speed operation conditions. To further reduce the torque ripples, the continuous control set (CCS) MPTC method is developed based on the constructed equivalent linear SRM model. The impossibility in analytically solving the optimization problem in the CCS MPTC method if using the original nonlinear SRM model is innovatively addressed by using the equivalent linear SRM model and properly modifying the cost function. Extensive simulation and experimental results prove the low-ripple feature of the proposed CCS MPTC method in a wide speed range. The high nonlinearity also makes the current control of SRM drives difficult. An intersection-method-based current controller is presented to ensure good current tracking performance for SRMs. The employed adaptive flux-linkage observer makes this current controller show robust performance when there is a deviation on the employed flux-linkage characteristics. Finally, the key but unmeasurable radial force information for the advanced acoustic reduction method is reconstructed based on the measured flux-linkage curves and some core relationship. This core relationship, which is between the square root of the radial force and the flux-linkage, is explored in detail. Simulation results reveal that the proposed method shows good radial force estimation accuracy when there is even 50% airgap length variation. / Thesis / Doctor of Philosophy (PhD)