Switched reluctance machines (SRMs) have recently attracted more interest in many applications due to the volatile prices of rare-earth permanent magnets (PMs) used in permanent magnet synchronous machines (PMSMs). They also have rugged construction and can operate at high speeds and high temperatures. However, acoustic noise and high torque ripples, in addition to the relatively low torque density, present significant challenges. Geometry and topology optimization are applied to overcome these challenges and enable SRMs to compete with PMSMs. Key geometric design parameters are optimized to minimize various objective functions within geometry optimization. On the other hand, the material distribution in a particular design space within the machine domain may be optimized using topology optimization. We discuss how these techniques are applied to optimize the geometries and topologies of SRMs to enhance machine performance. As optimizing the machine geometry and material distribution at the design phase is of substantial significance, this work offers a comprehensive literature review on the current state of the art and the possible trends in the optimization techniques of SRMs. The thesis also reviews different configurations of SRMs and stochastic and deterministic optimization techniques utilized in optimizing different configurations of the machine. This thesis introduces a new ON/OFF optimization method based on the line search method to overcome the limitations of the conventional annealing-based ON/OFF optimization. The proposed method shows a faster convergence to optimal solutions than the conventional annealing-based ON/OFF method. The thesis also compares the performance of the generative optimization and the topology optimization of a 6/14 switched reluctance machine with the proposed method and the conventional method. The two methods are applied to two different design domains of the machine for topology and generative optimization and the results are compared to the results of the annealing-based ON/OFF method. The results show the effectiveness of the newly proposed method. A new technique has been introduced in this thesis for reducing the time of calculating stator radial force density waves of switched reluctance machines (SRMs). The method is based on the finite element (FE) simulation of a fraction of an electrical cycle. The new approach shows that a significant time reduction is achieved as compared to the time required for stator radial force density calculation based on the one mechanical cycle simulation method. As the switched reluctance motors introduce new challenges in aspects such as acoustic noise, vibrations, and torque ripples, the method introduced in this helps reduce the time of the optimization process of switched reluctance machines in the design stage to improve the machine performance. The proposed method is applied to radial flux switched reluctance machines. Three different SRMs configurations were used to show the effectiveness of this technique in different force components with minimal error as compared to the benchmark method based on the FE simulation of one mechanical cycle. / Dissertation / Doctor of Philosophy (PhD)

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<p>The world transportation sector has been relying on the oil industry for more than a hundred years, accounting for the largest oil consumption and one third of the greenhouse gas emissions. However, with the boosting demand, escalating national energy security concerns and emerging environmental issues, reducing and displacing petroleum fuel in transportation sector has become an urging global target. As a result, hybrid electric vehicles evolve as one solution to displace petroleum fuel by utilizing vehicle onboard electrical systems, achieving higher fuel economy and less emissions by vehicle electrification and hybridization.</p> <p>However, since hybrid electric vehicles add additional electrical components and systems to realize better fuel economy, the system complexity increases and thus the cost increases. Hence, it is an objective of this thesis research to focus on the integrations and optimizations, aiming to simplify and optimize the hybrid power-trains in both system level and component level.</p> <p>This thesis contributes to a novel integrated electro-mechanical hybrid transmission that is potentially more compact and more operational flexible with fewer components compared to the GM Allison Two-Mode hybrid transmission. Comprehensive commercialized power-train transmissions are reviewed and analyzed to serve as background information for comparison. It also contributes to a family of double-rotor switched reluctance machines that are more integrated and suitable for hybrid electric vehicle applications. A prototype double-rotor switched reluctance machine has been built and tested for concept proving. Detailed machine design process is reported with the emphasis on design novelties. Finite element analysis and optimization techniques are applied and the accuracy is confirmed by the experiments. In addition, methods of machine loss analysis, thermal analysis and drive analysis are established; manufacturing and testing procedures are documented in detail that can be used for future machine designs guidance.</p> / Doctor of Philosophy (PhD)

Closer attention has been given to the acoustic noise performance of electric motors as electrified powertrains penetrate into the transportation system. Particularly, switched reluctance machines (SRMs) introduce a new challenge to the acoustic noise aspects given that the radial force harmonics can excite the natural frequencies of the main circumferential modes. A practical understanding of the radial force density decomposition is crucial in identifying the primary source of acoustic noise at different operating points, and it is one of the contributions of this thesis. An analytical expression is introduced to identify the temporal harmonic orders that excite different spatial mode shapes. The mode excitation is investigated along with the sound pressure level (SPL) produced by the primary vibrating mode shapes. Acoustic noise characteristics for each mode and the corresponding natural frequency at different speeds have been analyzed by using a waterfall plot. The acoustic noise generation by conventionally controlled SRMs prevents its use on applications where acoustic comfort is required. Acoustic noise is radiated by the stator frame when a vibration mode is excited by the respective spatial order at a forcing frequency that is close to the stator's modal natural frequency. The excitation surface wave is the radial force density waveform as a function of time and spatial position. From the harmonic content analysis, a phase radial force shaping method is for switched reluctance machines is proposed. A generic function for the radial force shape is identified, whose parameters are calculated by an optimization algorithm to minimize the torque ripple for a given average torque. From the phase radial force, a current reference is obtained. The proposed methodology is experimentally validated, with a four-phase 8/6 SRM, by acoustic noise measurements at different speeds and load torque conditions. / Thesis / Doctor of Philosophy (PhD)

High-accuracy electromagnetic design and analysis of electric machines is enhanced by the use of various numerical methods. These methods solve Maxwell’s equations to determine the distribution of the electric and magnetic fields throughout the considered machine structure. Due to the complicated architectures of the machines and the nonlinearity of the utilized magnetic materials, it is a very challenging task to obtain an analytical solution and, in most cases, only a numerical solution is possible. The finite element method (FEM) is one of the standard numerical methods for electromagnetic field analysis. The considered machine domain is divided into finite elements to which the field equations are applied. FEM solvers are utilized to develop optimization procedures to assist in achieving a design that meets the required specifications without violating the design constraints. The design process of electric machines involves adjusting the machine parameters. This is usually done through experience, intuition, and heuristic approaches using FEM software which gives results for various parameter changes. There is no guarantee that the achieved design is the optimal one. An alternative approach to the design of electric machines exploits robust gradient-based optimization algorithms that are guaranteed to converge to a locally-optimal model. The gradient-based approaches utilize the sensitivities of the performance characteristics with respect to the design parameters. These sensitivities are classically calculated using finite difference approximations which require repeated simulations with perturbed parameter values. The cost of evaluating these sensitivities can be significant for a slow finite element simulation or when the number of parameters is large. The adjoint variable method (AVM) offers an alternative approach for efficiently estimating response sensitivities. Using at most one extra not-iterative simulation, the sensitivities of the response to all parameters are estimated. Here, a MATLAB tool has been developed to automate the design process of switched reluctance motors (SRMs). The tool extracts the mesh data of an initial motor model from a commercial FEM software, JMAG. It then solves for magnetic vector potential throughout the considered SRM domain using FEM taking into consideration the nonlinearity of the magnetic material and the motor dynamic performance. The tool calculates various electromagnetic quantities such as electromagnetic torque, torque ripple, phase flux linkage, x and y components of flux density, air-region stored magnetic energy, phase voltage, and phase dynamic currents. The tool uses a structural mapping technique to parametrize various design parameters of SRMs. These parameters are back iron thickness, teeth height, pole arc angle, and pole taper angle of both stator and rotor. Moreover, it calculates the sensitivities of various electromagnetic quantities with respect to all these geometric design parameters in addition to the number of turn per phase using the AVM method. The tool applies interior point optimization algorithm to simultaneously optimize the motor geometry, number of turns per phase, and the drive-circuit control parameters (reference current, and turn-on and turn-off angles) to increase the motor average dynamic torque. It also applies the ON/OFF topology optimization algorithm to optimize the geometries of the stator teeth for proper distribution of the magnetic material to reduce the RMS torque ripple. A 6/14 SRM has been automatically designed using the developed MATLAB tool to achieve the same performance specifications as 6110E Evergreen surface-mounted PM brushless DC motor which is commercially available for an HVAC system. / Thesis / Doctor of Philosophy (PhD)

Switched reluctance machines (SRMs) are well known for their simple and robust structure, facilitating their increasing application in many sectors, for example vacuum cleaners, where domestic machines operate at high-speed, 50,000 RPM being typical. Conventional SRMs (CSRMs) use a decoupled concentrated phase winding so that torque is predominantly only generated due to the self-inductance, which limits utilization of the machine electrical circuits. In this thesis, the toroidal winding SRM (TSRM) is introduced, which operates based on the variation of mutual inductance between different phases. The toroidal winding introduces additional winding space, and the winding is practically easy to implement, both features that lead to a relatively higher copper filling factor. The toroidal winding also benefits the machine thermal performance, as the winding is directly exposed on the machine periphery and thus accessible to cooling. All these make TSRMs interesting and meaningful for further study. Following a comprehensive comparison of CSRM and TSRM characteristics, a general torque equation is presented that is applicable to both CSRM and TSRM. Two 12-switch converters are proposed to drive three-phase TSRMs. Moreover, sinusoidal current excitation with a commercial three-phase half-bridge converter has been suggested as an alternative converter solution for TSRMs. Accordingly, a three-phase six-stator-pole, four-rotor-pole CSRM is designed and optimized with a speed of up to 50,000 rpm in this thesis. A TSRM is resized to achieve the same envelope dimension as a benchmark CSRM. Thus, a comparative study between high-speed CSRM and TSRMs has been carried out. They have both been prototyped and tested. The findings suggest that the TSRM is superior, considering machine mass and wire temperature management. The TSRM has a better torque output at lower speeds because copper losses are dominant. However, the CSRM has more advantages at higher speeds due to lower iron losses and lower DC voltage requirements. / Thesis / Doctor of Philosophy (PhD)

A novel belt alternator starter (BAS) is proposed to replace the starter and alternator in a hybrid electric vehicle. The BAS designed utilizes an 18 rotor, 12 stator pole switched reluctance machine (SRM) configuration, with concentrated bar windings wound in parallel. Through iteration of various machine geometry parameters, the SRM can meet the torque and speeds demands over standardized drive cycles described by the US Environmental Protection Agency. / With the depletion of oil wells and changing global climate, a large emphasis is placed on the research, development and adoption of electric vehicles (EVs) to replace vehicles driven by internal combustion engines (ICEs). However the global supply chain is still not ready for such a large demand in EVs; therefore hybrid electric vehicles (HEVs) aim to ease the transition between ICEs and EVs. The research outlined in this thesis investigates the design of a 18 stator, 12 rotor pole (18/12) configuration switched reluctance machine (SRM) utilizing novel technologies for use as a belt alternator starter (BAS) motor in an HEV. Background research on current trends and technologies for electric motors and vehicles is performed before evaluating initial geometry for the motor core to be designed. Initial geometry is brought into JMAG to develop an electromagnetic model and begin the geometry optimization. The 18/12 design process highlights how changes to motor parameters from a geometry and winding standpoint will affect motor performance. After the motor core geometry yields suitable performance, a mechanical design is proposed encompassing the rotary assembly, cooling as well as solutions for mounting. / Thesis / Master of Applied Science (MASc) / Hybrid electric vehicles are becoming more prevalent as stricter restrictions are placed on fuel economy and emissions targets. Full electric vehicles on the other hand have not yet become the standard form of transportation due to the limits on range and infrastructure. Because of this, automotive manufacturers are researching and developing new methods in which they can meet these restrictions and limitations. Switched reluctance motors aim to be a solution to meet these demands while forging a new path by alleviating the demand on rare earth metals for the motor core. In this thesis, a design is proposed to fill an existing role in vehicle electrification best suited for a belted alternator starter.