Food banks have become an institutionalized response to helping individuals and families gain access to food as wages have stagnated, employment becomes more precarious, and social entitlements have dramatically declined over the years. Food banks were supposed to be a temporary stop gap measure in response to the recession of 1980. Thirty-three years later, food banks have proliferated across Canada in assisting a growing population in need of their services. I present an analysis of how food bank suppliers use the concept of hunger in a fundraising campaign called Canstruction® to understand how it relates to people’s perception of this social problem in our society. This qualitative research study uses discourse analysis to unpack the solicitation discourse used at Canstruction® events held in Waterloo and Toronto, Ontario in 2014. I have collected data from three different groups: persons who designed and installed their artwork at the Canstruction® Toronto event; persons who volunteer at a food bank; and people who have food insecurity experience. The findings indicate a differentiated understanding of hunger within the solicitation discourse for each research group: Canstruction® participants, food bank volunteers, and persons with food insecurity experience. The Canstruction® participants’ absorption of the solicitation discourse produced a limited understanding about hunger in our society. The food bank volunteer group agreed with the solicitation discourse but their images of hunger illustrated deeper criticisms of the event and food bank system. The participant group with food insecurity experience expressed the greatest amount of criticism against the food bank’s solicitation discourse and their images of hunger reflected their psycho-social experience of living in poverty. Also, an overwhelming majority of research participants with food insecurity wanted a food bank system that was more responsive to their needs and that honoured human dignity. My study on the social construction of hunger portrayed by food banks highlights how this knowledge is reinforced, reproduced and challenged through a food drive that creates packaged food items into artwork and from images described by research participants. These insights have the potential to shift the discourse away from the branding of hunger as a matter of charity and move towards discussing its fundamental causes: poverty and social inequality. / Thesis / Master of Social Work (MSW)

Examensarbetet var en utvärdering av en synkron trefas permanentmagnetmotor med utvändig rotor. Den är tänkt att ingå i ett batterimatat drivsystem för hjälputrustning på segelbåtar. Målen var att kartlägga prestandan i standardutförande samt att hitta de svaga punkterna i konstruktionen. Förslag på hur motorutförandet kan optimeras ska också läggas fram.   Tester och mätningar gjordes i en testuppkoppling med växelriktare, motor och axelkopplad generator. Detta för att kunna få fram fler mätvärden på motorn. Generatorn fick varvtalskortslutning när belastningsströmmen kom upp i 106,1 A och testerna fick avslutas. Koppartråden i lindningarna blev för varm och ytskiktet smälte. Testerna visar att motorn klarar av strömmar upp till 92,1 A och har då en verkningsgrad på 70 %. Det var lindningens strömtålighet tillsammans med effektförlusterna som var den begränsande faktorn i motorkonstruktionen.   Forcerad kylning i form av vattenkyld stator eller att öka lindningstrådens strömtålighet genom att t.ex. en större kabelarea är alternativ för att få till en bättre verkningsgrad och motorprestanda. Ser man till externa lösningar skulle luftkylning med fläkt kunna adderas. / The project was to evaluate a synchronous three-phase permanent magnet motor with brushless outrunner. It is supposed to be a part of an electric drive system for equipment onboard sailing boats. The goal was to investigate the performance of the motor and find the construction weaknesses and to come up with suggestions how to optimize the performance of the motor.   Tests and measurements were made with a test setup that consisted of inverter, motor and a generator connected to the shaft. The generator stator winding had a short circuit when the load current reached 106,1 A and the tests therefore had to end. The copper wire used in the windings temperature became to high and the isolation of the wire melted.  The tests showed that the motor could handle up to 92,1 A with an efficiency of 70%. It was how much current the winding could withstand together with the power losses that was the limiting factor of the motor construction.   Forced cooling with water cooled stator or improving the winding wires ability to handle higher currents by increasing the cable area are both alternatives to get a better efficiency and motor performance.

<p>In recent years, switch-mode power electronic converters have gained considerable popularity</p> <p>because of their compact size and high switching frequencies. This makes them</p> <p>suitable for power processing in various applications, including photovoltaic systems and</p> <p>electric vehicles. However, their high switching frequency capabilities have a drawback. A</p> <p>high-frequency common-mode voltage coupled with the switching of the power converters</p> <p>excites the parasitic capacitances of the system. It leads to the flow of common-mode current.</p> <p>Since the common-mode current flows through an unintended path, it can potentially</p> <p>interfere with the performance of system components. Passive filters can be used to mitigate</p> <p>common-mode currents. Using a common-mode inductor in conjunction with strategically</p> <p>placed capacitors makes it possible to limit the flow of common-mode current.</p> <p><br></p> <p>As part of this work, passive mitigation of common-mode current will be investigated in</p> <p>a variable frequency drive system. In this regard, the process of designing a three-phase ac</p> <p>common-mode inductor is explained. As a first step, a mitigation strategy is proposed and</p> <p>described. Next, the issue of self-capacitance of the inductor is discussed. Afterwards, the</p> <p>ac common-mode inductor is designed using a multi-objective optimization-based approach.</p> <p>Following this are the design results, concluding the dissertation.</p>

<p dir="ltr">There is a growing demand for lower-cost, lighter-weight, and more compact electric ma-<br>chines used for vehicle propulsion. In this research, a dual-rotor inert-core machine (ICM) is<br>considered to meet this demand. In the ICM, permanent-magnet-based Halbach arrays are<br>placed on inner and outer rotating structures. This enables one to eliminate magnetic steels<br>used in the stator and rotor of traditional electric machinery. In addition, a stator structure<br>that leverages a thermal plastic is proposed that facilitates straightforward active cooling<br>of phase windings, which greatly increases current density. To support the multi-objective<br>design of the ICM, a multi-physics toolbox has been developed. Within the toolbox, electro-<br>magnetic performance is predicted using a method-of-moments-based field solver. Thermal<br>performance is assessed using a thermal equivalent circuit that includes conductive heat<br>transfer from stator windings to the surrounding environment as well as convective heat<br>transfer to moving fluids. The structural integrity of the stator is assessed using analytical<br>expressions to predict stress from material properties, geometry, and applied external forces.<br>Calculated loss of proposed designs includes those of the stator windings as well as those<br>required for active cooling. Several optimization studies have been conducted to evaluate the<br>performance of the ICM under an expected electric vehicle driving cycle. From the studies,<br>Pareto-optimal fronts are obtained and used to explore the impact of alternative cooling<br>strategies on volumetric power density.</p>

No description available.

<p>As a cost-effective, healthy, and environmentally friendly personal mode of transportation, electric bicycles (E-bikes) are gaining an increasing market share from conventional bicycles and automobiles. Considering the legal rules in Ontario, Canada, a 500W motor makes the E-bike more attractive for travelling use. At the same time, the simple structure, high torque and power density, as well as the low cost of the switched reluctance machine (SRM) makes it a strong candidate for E-bikes.</p> <p>In this thesis, a 3-phase, external-rotor SRM with 6 stator poles and 10 rotor poles is designed for E-bike. The design of an external rotor arrangement of the 6-10 SRM topology has not previously been reported, hence it offers a new contribution to the published works. The machine design is initiated by the output power equation and is followed by a comprehensive finite element analysis (FEA). The external-rotor arrangement is chosen to facilitate ease of integration into the wheel hub structure of a typical pedal bicycle. The increasing rotor poles yield improved torque ripple reduction than more conventional (i.e. 6-4, 12-8 etc.) SRM design, which is an essential feature for low speed rider comfort.</p> <p>A new torque ripple reduction control scheme is investigated. Although the comparison shows that the torque sharing function has more positive result than angular position control with regards to torque ripple, this is at the expense of higher losses. Detailed thermal analysis ensures this machine is suitable to require no additional cooling system. The final machine design is experimentally tested via a full system prototype. Results highlight some limitation of the 2-D FEA in terms of the winding inductance calculation. Here, the end winding introduce more influence on short thickness machine, which will reduce its output power. However, its power-speed curve shows that this prototype machine has very strong overload ability.</p> / Master of Applied Science (MASc)

The increasing shift towards more electric or all electric aircraft urgently necessitates dc/ac converter systems with high power density. Silicon Carbide (SiC) devices, known for their superior performance over traditional silicon-based devices, facilitate this increase in power density. Nonetheless, achieving optimal power density faces challenges due to the unique requirements and conditions of aircraft applications. A primary obstacle is optimizing the topology and parameters of the dc/ac converter system to achieve high power density while adhering to the stringent aerospace EMI standard DO-160 and bearing current limitations. Electric aircraft demand unmatched reliability, necessitating strict control over EMI noise and bearing currents. These considerations significantly impact the selection of topology and parameters to maximize power density. This dissertation assesses how dc voltage, topology, and switching frequency affect component weight, seeking an optimal mix to enhance power density. The methodology and conclusions are validated through a 200-kW motor drive system designed for electric aircraft. Moreover, traditional dc/ac systems are burdened by the weight and space occupied by separate current sensors and short-circuit protection circuits. This work introduces two innovative current sensors that integrate device current sampling with the functionality of traditional shunt resistors, AC hall sensors, and short-circuit protection circuits, thus improving system density and bandwidth. The first sensor, a PCB-based Rogowski coil, integrates with the gate driver and commutation loops, enhancing power density despite challenges in managing CM noise. The second sensor utilizes parasitic inductance in the power loop, with an integrator circuit and an adaptive compensation algorithm correcting errors from parasitic resistance, ensuring high bandwidth accuracy without needing parasitic resistance information. Variable operation conditions from motors pose another challenge, potentially leading to oversized inverters due to uneven loss distribution among switching devices, exacerbated at extreme operating points like motor start-up. This dissertation investigates the loss distribution in multi-level T-Type neutral point clamped (NPC) topology and proposes a novel loss-balance modulation scheme. This scheme ensures even loss distribution across switches, independent of power factor and modulation index, and is applicable to T-type inverters of any level count. Finally, thermal management and insulation at high altitudes present significant challenges. While power devices may be cooled using conventional liquid cooling solutions, components like AC and EMI filters struggle with complex geometries that can create hot spots or high E-field points, complicating filter design for high current applications. A comprehensive design and optimization methodology based on planar heavy-copper PCB design is proposed. By utilizing flexible 2D or 3D E-field shaping and maximizing thermal transfer from copper to ambient, this methodology significantly improves power density and ensures effective heat dissipation and insulation at altitudes up to 50,000 feet. / Doctor of Philosophy / The increasing shift towards more electric or all electric aircraft urgently necessitates dc/ac converter systems with high power density. Silicon Carbide (SiC) devices, known for their superior performance over traditional silicon-based devices, facilitate this increase in power density. Nonetheless, achieving optimal power density faces challenges due to the unique requirements and conditions of aircraft applications. A primary obstacle is optimizing the topology and parameters of the dc/ac converter system to achieve high power density while adhering to the stringent aerospace EMI standard DO-160 and bearing current limitations. Electric aircraft demand unmatched reliability, necessitating strict control over EMI noise and bearing currents. These considerations significantly impact the selection of topology and parameters to maximize power density. This dissertation assesses how dc voltage, topology, and switching frequency affect component weight, seeking an optimal mix to enhance power density. The methodology and conclusions are validated through a 200-kW motor drive system designed for electric aircraft. Moreover, traditional dc/ac systems are burdened by the weight and space occupied by separate current sensors and short-circuit protection circuits. This work introduces two innovative current sensors that integrate device current sampling with the functionality of traditional shunt resistors, AC hall sensors, and short-circuit protection circuits, thus improving system density and bandwidth. The first sensor, a PCB-based Rogowski coil, integrates with the gate driver and commutation loops, enhancing power density despite challenges in managing CM noise. The second sensor utilizes parasitic inductance in the power loop, with an integrator circuit and an adaptive compensation algorithm correcting errors from parasitic resistance, ensuring high bandwidth accuracy without needing parasitic resistance information. Variable operation conditions from motors pose another challenge, potentially leading to oversized inverters due to uneven loss distribution among switching devices, exacerbated at extreme operating points like motor start-up. This dissertation investigates the loss distribution in multi-level T-Type neutral point clamped (NPC) topology and proposes a novel loss-balance modulation scheme. This scheme ensures even loss distribution across switches, independent of power factor and modulation index, and is applicable to T-type inverters of any level count. Finally, thermal management and insulation at high altitudes present significant challenges. While power devices may be cooled using conventional liquid cooling solutions, components like AC and EMI filters struggle with complex geometries that can create hot spots or high E-field points, complicating filter design for high current applications. A comprehensive design and optimization methodology based on planar heavy-copper PCB design is proposed. By utilizing flexible 2D or 3D E-field shaping and maximizing thermal transfer from copper to ambient, this methodology significantly improves power density and ensures effective heat dissipation and insulation at altitudes up to 50,000 feet.

The present work studies the disturbances created in the electric system of a pumped storage power plant, which is an hydraulic generation facility where the machines can work as turbines or pumps, by the operation of a static frequency converter (SFC). The SFC is used for starting the synchronous machines at the station when in the pump mode. During the starting process several equipment is connected to the SFC being possible to get affected by the disturbances generated. These disturbances mainly include the creation of transient overvoltages during the commutation of the semiconductor devices of the SFC and the introduction of harmonics in the network currents and voltages. This work analyzes the possible effects of the SFC operation over the station equipment based on computer simulations. For this purpose, the complete system was modeled and the starting process simulated in a computer transient simulator program. The work begins with a general review of the effects of electric disturbances over high voltage equipment and in particular of the disturbances generated by power electronics conversion equipment. Then the models for the different kind of equipment present in the system are discussed and formulated. The control system that governs the operation of the SFC during the starting process is analyzed later as well as the operation conditions. Once the model of the system is set up, the harmonic analysis of the electric network is done by frequency domain and time domain methods. Time domain methods are also employed for the analysis of the commutation transient produced by the SFC operation. Finally, the simulation results are used to evaluate the impact of the SFC operation on the station equipment, especially on the generator step up transformer. / Master of Science

Power electronics is inevitably concerned with the processing of variable speed power generations such as in wind turbines, aircraft systems and naval on-board ship systems. The nature of these types of energy is distinct in that their frequency and power vary depending on the speed of the prime-mover. To make use of the variable speed energy, a power processing scheme which transforms the variable speed energy into a constant frequency power is required. There are measures such as mechanical and electrical links for such purposes. Electrical link systems are chosen in this study due to their fast responses and high reliabilities. The power conversion stage may be a dc link with a line-commutated converter, a dc link with a self-commutated inverter, or a cycloconverter. The line-commutated converter and cycloconverter power stages require a fixed frequency supply for operation whereas the self-commutated inverter is capable of stand-alone operation, thus making it attractive. Two cases of variable speed power generation using a permanent magnet synchronous machine (hereafter referred to as PMSM) and a switched reluctance machine (hereafter referred to as SRM) were studied in this dissertation. The possible use of PMSMs has been proved by the good correlation between the experimental results and the theoretically predicted results. Three different control strategies have been proposed, implemented in hardware, and experimentally verified. The efficiency of the VSCF power conversion with a self commutated converter were comparable to the one using a line-commutated converter. A novel converter topology with no dc link capacitor has been proposed for the application of SRMs to the VSCF power conversion. The proposed topology directly links the constant frequency ac source to the SRM. This feature enhances the reliability of the power conversion scheme and reduces the weight and volume of the system. The correlation between the theoretical and experimental results of some key issues showed the feasibility of the proposed VSCF power conversion scheme. In the course of the study, one stage ac to dc power conversion with a compact transformer was required for dc loads. However, phase-controlled ac to dc conversion has the disadvantages of low power factor and harmonic pollution on the utility side, particularly in the case where dc voltage regulation is required. Therefore, a novel single phase rectifier for dc load which provides ohmic isolation with a high frequency transformer is extensively investigated. The proposed scheme had a wide output variation on dc output while maintaining unity power factor and sinusoidal current in the ac input side. Three control strategies for the operation of the converter were proposed and verified experimentally. The harmonic spectra on ac and dc sides are analytically derived and experimentally proved under some load conditions. / Ph. D.

A novel multilevel converter that is especially suited for high speed multi-megawatt switched reluctance motor drives operating at the medium voltage level is presented. The drive is capable of variable speed, four-quadrant operation. Each phase leg of the converter contains an arbitrary number of cascaded cells connected in series with the phase winding. Each cell contains a half-bridge chopper connected to a capacitor. The converter is named the cascaded chopper cell converter. The modular nature of the converter with the ability to add redundant cells makes it very reliable, which is a key requirement for medium voltage drive applications. A comprehensive control algorithm that overcomes the challenges of balancing and controlling cell capacitor voltages is also proposed. A suitable startup algorithm to limit startup current and switching losses, as well as ensure that cell capacitor voltages remain controlled at startup, is suggested. Details of the drive design such as component sizing and control parameter selection are also discussed. A detailed simulation model is developed and explained, and simulation results are provided for primary validation. Operation with standard current and speed control is first simulated. Then a scheme that gives way to a controller that operates the drive in single-pulse mode is developed and presented. This single-pulse control scheme controls the turn-on and turn-off angles, as well as the energization voltage level, in order to obtain high efficiency. Practical considerations related to the drive such as reliability, efficiency, and cost considerations are also discussed. Finally, a detailed comparison of the proposed converter to another competing converter is performed. Besides its scalability to high voltages and powers, the reliability and efficiency of the proposed converter makes it also a candidate for sub-megawatt applications requiring minimum downtime, or any application where high efficiency or improved performance is required. A small part of this work is also dedicated to brushless dc machines. Control methods for a new converter for brushless dc machines are proposed and verified via simulation. The main advantage of this converter with the proposed control is that it allows exact control of torque or speed up to twice the rated speed, without resorting to current phase advancing or other flux-weakening techniques. / Ph. D. / Electric motors are used in a very wide range of applications. They are found in power tools, in household appliances like washers and dryers, in compressors for HVAC, in fans, blowers and pumps in industry, and in electric vehicles and electric transit systems, only to name a few. An electric motor that is combined with an electronic circuit that allows precise control of the motor speed and torque is referred to as an electric drive. Very large electric drives – reaching multi-megawatt powers – are used in several applications such as in ship propulsion, in large pumps for moving water and sewage, and others. Very few electric motor drive options currently exist at that power level, and so multi-megawatt electric motor drives present an interesting research opportunity. This work proposes a novel drive system that is best suited for high speed multi-megawatt electric drives employing the switched reluctance motor. The switched reluctance motor was chosen due to its robustness, high efficiency, and high speed capability. A novel electronic converter that is scalable to high power and voltage levels is proposed. It features high reliability which is essential in multi-megawatt applications that typically require very high uptime. It has a modular structure, thereby allowing for simple construction. A comprehensive control algorithm for the drive system consisting of the converter and motor is proposed. Also a suitable algorithm that keeps the electrical and thermal variables within the allowed limits during the startup stage is proposed. A detailed simulation model is developed and explained, and simulation results are provided for primary validation. Next, a control scheme that results in high efficiency through appropriate control of the drive’s various parameters is proposed. Practical considerations related to the drive such as reliability, efficiency, and cost considerations are also discussed. Finally, a detailed comparison of the proposed converter with another competing converter is performed. Besides its scalability to high voltages and powers, the reliability and efficiency of the proposed converter makes it also a candidate for sub-megawatt applications requiring minimum downtime, or any application where high efficiency or improved performance is required. A small part of this work is also dedicated to drives using another type of machine called the brushless dc motor. Control methods for a new converter for brushless dc machines are proposed and verified via simulation. The main advantage of this converter with the proposed control is that it allows exact control of torque or speed up to twice the rated speed, which makes it useful in traction applications.