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In reference to IEEE copyrighted material which is used with permission in this thesis, the IEEE does not endorse any of McMaster University's products or services. Internal or personal use of this material is permitted. If interested in reprinting/republishing IEEE copyrighted material for advertising or promotional purposes or for creating new collective works for resale or redistribution, please go to http://www.ieee.org/publications_standards/publications/rights/rights_link.html to learn how to obtain a License from RightsLink. / The need for reductions in global greenhouse gas emissions, coupled with rising fuel prices, has motivated intense research in the area of hybrid and fully electric crafts for commercial applications in the aviation sector. This thesis explores implementation of Halbach arrays in high-speed radial flux machines (RFMs) and low-speed axial flux machines (AFMs) for aerospace applications. Highly accurate analytical equations are developed for quickly predicting the magnetic field in the latter (both for coreless and steel core stators) due to the complex three dimensional axial flux paths which make traditional finite element analysis time-consuming. Electromagnetic design and optimization of two aerospace machines that use Halbachs are detailed. The first is a ~14 kW AFM intended to replace an existing high lift motor RFM concept in NASA’s Maxwell X57 all-electric plane. Two design variants are selected which achieve a 10 % increase in torque/power and a 10 % decrease in mass/volume, respectively. The second machine is a 20,000 RPM surface permanent magnet RFM capable of 150 kW peak power output that is intended as a proof-of-concept for the later development of a megawatt machine for a hybrid and/or all-electric aircraft. / Thesis / Master of Applied Science (MASc)

Dagens samhälle har utvecklats till ett stort globalt system där människan fått en signifikant påverkan på klimatet och miljön. För att nå målet i Parisavtalet är det många sektorer som behöver ställa om sina verksamheter till att bli hållbara. Det gäller i allra högsta grad flygsektorn som har stora utmaningar framför sig när det gäller att minska sitt klimatavtryck. En av möjligheterna för att väsentligt minska flygets klimatpåverkan är att övergå till flygplan som drivs med hjälp av batterier istället för fossila bränslen.I det här projektet undersöks om de tekniska och infrastrukturmässiga förutsättningarna finns för att elflyg ska kunna ersätta den befintliga flygtrafiken mellan Stockholm och Visby och när i tiden en sådan förändring kan ske. Litteraturstudier och intervjuer har använts för att utforska det nuvarande kunskapsläget som är relevant för elflyg inom batteriteknik, elmotorer, aerodynamik samt infrastruktur på de relevanta flygplatserna. Med den utgångspunkten har en matematisk modell använts för att studera om de rådande tekniska förutsättningarna är tillräckliga eller om förbättringar kommer krävas. Det som framkom var att det i teorin är möjligt att tillverka ett elflygplan som kan flyga hela sträckan med befintlig teknik men att utveckling av både batteriteknik och aerodynamik sannolikt kommer krävas när andra aspekter vägs in. Infrastrukturen på flygplatserna är dessutom inte anpassade för elflyg i dagsläget, vilket leder till att det i ett optimistiskt scenario kommer gå att elektrifiera flygtrafiken mellan Stockholm och Visby inom 10 år. / Today's society has evolved into a large global system where people have a significant impact on the climate and the environment. To achieve the goal of the Paris Agreement, many sectors need to change their business to become sustainable. This is very much the case for the aviation sector, which has major challenges ahead when it comes to reducing its climate footprint. One of the opportunities to significantly reduce the climate impact of aviation is to switch to aircraft powered by batteries instead of fossil fuels. This project examines whether the technical and infrastructure conditions are in place for electric aircraft to replace the existing air traffic between Stockholm and Visby and when such a change can occur in time. Literature studies and interviews have been used to explore the current state of knowledge relevant to electric aviation within battery technology, electric motors, aerodynamics and infrastructure at the relevant airports. Based on this, a mathematical model has been used to study whether the current technical conditions are sufficient or if improvements will be required. What emerged was that, in theory, it is possible to produce an electric aircraft that can fly the entire distance with existing technology, but that development of both battery technology and aerodynamics is likely to be required when other aspects are taken into account. The infrastructure at the airports is also not adapted for electric flights yet, which means that in an optimistic scenario it will take up to 10 years before air traffic can be fully electrified between Stockholm and Visby.

Combustion emissions from aviation operations contribute significantly to climate change and air pollution. Accordingly, there is increasing interest in advancing battery-powered propulsion for aviation applications to reduce emissions. As batteries continue to improve, it is essential to recognize breakthroughs in battery specific energy in the context of air transport vehicles. Most electric aircraft designs and programs have focused on small aircraft because of restrictive battery performance. This work presents a feasibility assessment for an all-electric airliner based on an Airbus A220-100 with turbofan engines replaced by electric motors and propellers. The analysis compares the performance characteristics of the electric airliner to the A220-100 and establishes several configurations with varying battery pack-specific energy. The short-term electric airliner could replace conventional aircraft on very short, high-density missions. In contrast, the long-term electric airliner requires significant battery technology improvements that are not currently foreseen. The alternative long-term electric airliner could complete half of the A220-100’s missions, but the necessary specific energy value is also not anticipated shortly. All-electric airliners would significantly impact manufacturing, operations, costs, and emissions but are commercially infeasible with current battery technology. Additional development of more advanced battery technology is required to increase the specific energy of battery packs, enhance battery safety and reliability, and develop lighter high-power electric motors.

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Insulation system is an inseparable part of electrical equipment. In this study, one of the most important aging factors in insulation systems known as partial discharge (PD) is targeted. PD phenomenon has been studied for more than a century and yet new technologies still demand the investigation of PD impact. Nowadays, electrification is penetrating into various fossil-fuel-based industries such as transportation system that demands the reliability of electrical equipment under various harsh environmental conditions. Due to the lack of knowledge on the behavior of insulation systems, research in this area is intensively needed. The current study probes into the partial discharge phenomenon from two aspects and the groundwork for both aspects are provided by experimentation of multiple PD types. In the first goal, a finite-element analysis (FEA) approach is developed based on measurement data to estimate electric field distribution. The FEA model is coupled with a programming scheme to evaluate PD conditions, calculate PD metrics, and perform statistical analysis of the results. For the second target, it is aimed to use deep neural networks to identify and discriminate different sources of PD. The measurement data are used to generate thousands of phase-resolved PD (PRPD) images that will be used for training deep learning models. To meet the characteristics of the dataset, a deep residual neural network is designed and optimized to discriminate PD sources in an accurate, stable, and time-efficient way. The outcome of this research enhances the reliability of electrical apparatus through a better understanding of the PD behavior and lays a foundation for automatic monitoring of PD sources. / Doctor of Philosophy / Electrical equipment functions properly when its conductive elements are electrically insulated. The science of dealing with insulation systems has become more prominent in recent years due to the novel challenges and circumstances introduced by the rapid electrification trend. As an instance, the electrification trend in transportation systems can impose a multitude of environmental, thermal, and mechanical constraints which were not traditionally considered. These new challenges have led to an accelerated deterioration rate of insulation materials. To address this concern, this study targets the experimentation and modeling of the main aging mechanism in electrical equipment known as partial discharge (PD). A numerical model based on finite-element analysis (FEA) is developed that agrees with the test results and can accurately predict the aging of insulating materials due to the PD phenomenon. Moreover, the growing interest toward electrification of the aviation industry (as a response to the climate change crisis) requires the study of insulating materials under low-pressure (high-altitude) conditions. Theoretical and experimental data confirm the more frequent occurrence of PDs and their higher intensity under low-pressure conditions. Safety of operation is the highest priority in airborne transportation, yet no study has addressed the condition monitoring system as a necessary asset of the electric aircraft. To address this research gap, this work develops a dielectric online condition monitoring system (DOCMS) that actively monitors the deterioration level of insulation using deep learning methods. Based on standardized measurements under low-pressure conditions, the data are preprocessed to train the deep neural network with the pattern of PD activities. The proposed scheme can achieve >82% with short-term signals emitted measured from the system.

Today, we see a renewed interest in aircraft with multiple propellers. To support conceptual design of these vehicles, one of the major needs is a fast and accurate method for estimating wing aerodynamic characteristics in the presence of multiple propellers. For the method to be effective, it must be easy to use, have rapid turnaround time and should be able to capture major wing–propeller interaction effects with sufficient accuracy. This research is primarily motivated by the need to assess the effectiveness of computational fluid dynamics (CFD) for simulating aerodynamic characteristics of wings with multiple propellers. The scope of the present research is limited to investigating the interaction between a single tractor propeller and a wing. This research aims to compare computational results from a Reynolds-Averaged Navier-Stokes (RANS) method, StarCCM+, and a vortex lattice method (VLM), VSP Aero. Two configurations that are analysed are 1) WIPP Configuration (Workshop for Integrated Propeller Prediction) 2) APROPOS Configuration. For WIPP, computational results are compared with measured lift and drag data for several angles of attack and Mach numbers. StarCCM+ results of wake flow field are compared with WIPP's wake survey data. For APROPOS, computed data for lift-to-drag ratio of the wing are compared with test data for multiple vertical and spanwise locations of the propeller. The results of the simulations are used to assess the effectiveness of the two CFD methods used in this research. / Master of Science / Today, we see a renewed interest in aircraft with multiple propellers due to an increasing demand for vehicles which fly short distances at low altitudes, be it flying taxis, delivery drones or small passenger aircrafts. To support conceptual design of vehicles, one of the major needs is a fast and accurate method for estimating wing aerodynamic characteristics in the presence of multiple propellers. For the method to be effective, it must be easy to use, have rapid turnaround time and should be able to capture major wing–propeller inter- action effects with sufficient accuracy. This research is primarily motivated by the need to assess the effectiveness of computational fluid dynamics (CFD) for simulating aerodynamic characteristics of wings with multiple propellers. Then only can we can take full advantage of the capabilities of the CFD methods and support design of emerging propeller driven air vehicles with an appropriate level of confidence. This research aims to compare high level methods with increasingly complex geometries and realistic models of physics like Reynolds Averaged Navier Stokes (RANS) and low level methods that rely on simplified geometry and simplified physics models like Vortex Lattice Methods (VLM). We will analyse multiple configurations and validate them against experi- mental data and thus assessing the effectiveness of the CFD models. This research investigates two configurations, 1) WIPP configuration 2) APROPOS configuration, for which experimental data is available. The results of the simulations are used to assess the effectiveness of the two CFD methods used in this research.

The United States Air Force is in the process of developing a more electric aircraft. The development of an aircraft Integrated Power Unit and an Internal Starter/Generator will be instrumental in producing sufficient electrical power to run all non propulsive systems. Iron-cobalt alloys, such as Hiperco alloy 50HS, are high temperature, high strength magnetic materials ideal for these power applications. Design requirements and previous studies indicate that these materials need to survive in temperatures up to 1000F (810K), rotation speeds of about 55,000 rpm, and have strengths in excess of 80 ksi. Research conducted by Fingers provided the material and creep properties used in the analysis presented in this report. The finite element method was used to analyze a spinning rotor mounted to a circular shaft via an interference fit subjected to various operating environments. The power law creep model defined by Fingers was used to analyze three distinct rotor configurations. The first configuration was a constant temperature single lamina, mounted to a shaft of equal thickness, subject to temperatures between 727K and 780K, rotation speeds between 35,000 rpm and 60,000 rpm, and two different interference fits: 0.0015 inches and 0.003 inches. The results yield conservative predictions that indicate that these models could not survive the required operating conditions. The second configuration was a linear radial variation in temperature single lamina, mounted to a shaft of equal thickness, subjected to three temperature ranges, rotation speeds between 30,000 rpm and 55,000 rpm, and two different interference fits; 0.0015 inches and 0.003 inches. These results represent a more realistic model, which indicate that the "cooler" inner portions of the rotor restrict the creep deformations of the "hotter" outer portions resulting in higher possible operating temperatures and rotation speeds very near the required operating conditions. The third configuration was a lamina stack comprised of two rotor lamina, with a Coulomb friction surface interaction, and held together by a compressive axial force. These models represent a first step towards understanding the behavior of the entire rotor stack. / Master of Science

In the past two decades the core aircraft technology is going through a drastic change. The traditional technologies that is almost half a century old, is going through a complete revamp. In the new “More Electric Aircraft” technology many mechanical, pneumatic and hydraulic systems are being replaced by electrical and power electronic systems. Airbus-A380, Boeing B-787 are the pioneers in the family of these new breed of aircrafts. As the aircraft technology is moving towards “More Electric”, more and more electric motors and motor controllers are being used in new aircrafts. Number of electric motor drive systems has increased by about ten times in more electric aircrafts compared to traditional aircrafts. Weight of any electric component that goes into aircraft needs to be low to reduce the overall weight of aircraft so as to improve the fuel efficiency of the aircraft. Hence there is an increased need to reduce weight of motors and motor controllers in commercial aircraft. High speed ironless axial flux permanent magnet brushless dc motors are becoming popular in the new more-electric aircrafts because of their ability to meet the demand of light weight, high power density, high efficiency and high reliability. However, these motors come with very low inductance, which poses a big challenge to the motor controllers in controlling the ripple current in motor windings. Multilevel inverters can solve this problem. Three-level inverters are proposed in this thesis for driving axial flux BLDC motors in aircraft. Majority of the motors in new more electric aircrafts are in the power range of 2kW to 20kW, while a few motor applications being in the range of 100kW to 150kW. Motor controllers in these applications run from 270Vdc or 540Vdc bus which is the standard in new more electric aircraft architecture. Multilevel Inverter is popular in the industry for high power and high voltage applications, where high-voltage power switching devices like IGBT, GTO are popularly used. However multilevel inverters have not been tried in the low power range which is appropriate for aircraft applications. A detail analysis of practical feasibility of constructing three-level inverter in lower power and voltage level is presented in this thesis. Analysis is presented that verify the advantages of driving low voltage and low power (300Vdc to 600Vdc and less than 100kW) motors with multilevel inverters. Practical considerations for design of MOSFET based three-level inverter are investigated and topological modifications are suggested. The effect of clamping diodes in the diode clamped multilevel inverters play an important role in determining its efficiency. SiC diodes are proposed to be used as clamping diodes. Further, it is realised that power loss introduced by reverse recovery of MOSFET body diode prohibits use of MOSFET in hard switched inverter legs. Hence, a technique of avoiding the reverse recovery losses of MOSFET body diode in three-level NPC inverter is conceived. The use of proposed multilevel inverter topology enables operation at high switching frequency without sacrificing efficiency. High switching frequency of operation reduces the output filter requirement, which in turn helps reducing size of the inverter. In this research work elaborate trade-off analysis is done to quantify the suitability of multilevel inverters in the low power applications. For successful operation of three-level NPC inverter in aircraft electrical system, it is important for the DC bus structure in aircraft electric primary distribution system to be compatible to drive NPC inverters. Hence a detail study of AC to DC power conversion system as applied to commercial aircraft electrical system is done. Multi-pulse rectifiers using autotransformers are used in aircrafts. Investigation is done to improve these rectifiers for future aircrafts, such that they can support new technologies of future generation motor controllers. A new 24-pulse isolated transformer rectifier topology is proposed. From two 15º displaced 6-phase systems feeding two 12-pulse rectifiers that are series connected, a 24-pulse rectifier topology is obtained. Though, windings of each 12-pulse rectifiers are isolated from primary, the 6-phase generation is done without any isolation of the transformer windings. The new 24-pulse transformer topology has lower VA rating compared to standard 12-pulse rectifiers. Though the new 24-pulse transformer-rectifier solution is robust and simple, it adds to the weight of the overall system, as compared to the present architecture as the proposed topology uses isolated transformer. Non-isolated autotransformer cannot provide split voltage at the dc-link that creates a stable mid-point voltage as required by the three-level NPC inverter. Hence, a new front-end AC-DC power conversion system with switched capacitor is conceived that can support motor controllers driven by three-level inverters. Laboratory experimental results are presented to validate the new proposed topology. In this proposed topology, the inverter dc-link voltage is double the input dc-link voltage. An intense research work is performed to understand the operation of Trapezoidal Back EMF BLDC motor driven by three-Level NPC inverter. Operation of BLDC motor from three-Level inverter is primarily advantageous for low inductance motors, like ironless axial flux motors. For low inductance BLDC motor, very high switching frequency is required to limit the magnitude of ripple current in motor winding. Three-level inverters help limiting the magnitude of motor ripple current without increasing the switching frequency to very high value. Further, it is analysed that dc link mid-point current in three-level NPC inverter for driving trapezoidal BLDC motor has a zero average current with fundamental frequency same as switching frequency. Because of this, trapezoidal BLDC motors can easily be operated from three-level NPC inverter without any special attention given to mid-point voltage unbalance. One non-ideal condition arrives in practical implementation of the inverter that leads to non-zero average mid point current. Unequal gate drive dead time delays from one leg to other leg of inverter introduce dc-link mid-point voltage unbalance. For the motoring mode operation of trapezoidal BLDC motor drive, simple gate drive logic is researched that eliminates need of the gate drive dead-time, and hence solves the mid-point voltage unbalance issue. Simple closed loop control scheme for mid-point voltage balancing also is also proposed. This control scheme may be used in applications where very precise control of speed and torque ripple is warranted. All the investigations reported in this thesis are simulated extensively on MATHCAD and MATLAB platform using SIMULINK toolbox. A laboratory experimental set-up of three-Level inverter driving axial flux BLDC motor is built. The three-level inverter, operating from 300Vdc bus is built using 500V MOSFETs and 600V SiC diodes. All the control schemes are implemented digitally on digital signal processor TMS320F2812 DSP platform and GAL22V10B platforms. Experimental results are collected to validate the theoretical propositions made in the present research work. At the end, in chapter 5, some future works are proposed. A new external voltage balance circuit is proposed where the inverter dc-link voltage is same as the input dc-link voltage. This topology is based on the resonant converter principle and uses a lighter resonant inductor than prior arts available in literature. Detail simulation and experimentation of this topology may be carried out to validate the industrial benefits of this circuit. It is also thought that current source inverters may work as an alternative to voltage source inverters for driving BLDC motors. Current source inverters eliminate use of bulky DC-link capacitors. Long term reliability of current source inverters is higher than voltage source inverters due to the absence of possibility of shoot-through. Further, in voltage source inverters, the voltage at the motor terminal is limited by the source voltage (dc-link voltage). This issue is eliminated in current source inverters. An interface circuit is conceived to reduce the size of dc-link inductors in current source inverters, pending detail analysis and experimental verification. The interface circuit bases its fundamentals on the principles of operation of multilevel inverters for BLDC motors that is presented in this thesis.

<p dir="ltr">Electric aircraft offer a promising avenue for reducing aviation's environmental impact through decreased greenhouse gas emissions and noise pollution. Nonetheless, their adoption is hindered by the challenge of limited operational range. Addressed in the study is the range limitation by integrating and optimizing multiple energy storage components—hydrogen fuel cells, Li-ion batteries, and ultracapacitors—through advanced energy management strategies. Utilizing meta-heuristic optimization methods, the research assessed the dynamic performance of each energy component and the effectiveness of the energy management strategy, primarily measured by the hydrogen consumption rate. MATLAB simulations validated the proposed approach, indicating a decrease in hydrogen usage, thus enhancing efficiency and potential cost savings. Artificial Gorilla Troop Optimization yielded the best results with the lowest average hydrogen consumption rate (102.62 grams), outperforming Particle Swarm Optimization (104.68 grams) and Ant Colony Optimization (105.96 grams). The findings suggested that employing a combined energy storage and optimization strategy can significantly improve the operational efficiency and energy conservation of electric aircraft. The study highlighted the potential of such strategies to extend the range of electric aircraft, contributing to a more sustainable aviation future.</p>