Photovoltaic (PV) systems are a rapidly growing segment in the renewable energy industry.  Though they have humble origins and an uncertain future, the commercial viability of PV has significantly increased, especially in the past decade.  In order to make PV useful, however, significant effort has to go into the power conditioning systems that take the low-voltage dc from the panel and create utility compatible ac output.  Popular architectures for this process include the centralized inverter and the distributed micro-inverter, each with its own advantages and disadvantages.  One attempt to retain the advantages of both architectures is to centralize the inverter function but construct PV panel-level micro-converters which optimize the panel output and condition the power for the inverter.  The main focus of this work is to explore the technical challenges that face the evolution of the dc-dc micro-converter and to use them as a template for a vertically integrated design procedure. The individual chapters focus on different levels of the process:  topology, modulation and control, transient mitigation, and steady-state optimization.  Chapter 2 introduces a new dc-dc topology, the Integrated Boost Resonant (IBR) converter, born out of the natural design requirements for the micro-converter, such as high CEC efficiency, simple structure, and inherent Galvanic isolation.  The circuit is a combination of a traditional PWM boost converter and a discontinuous conduction mode (DCM), series resonant circuit.  The DCM operation of the high-frequency transformer possesses much lower circulating energy when compared to the traditional CCM behavior.  When combined with  zero-current-switching (ZCS) for the output diode, it results in a circuit with a high weighted efficiency of 96.8%.  Chapter 3 improves upon that topology by adding an optimized modulation scheme to the control strategy.  This improves the power stage efficiency at nominal input and enhances the available operating range.  The new, hybrid-frequency method utilizes areas where the modulator operates in constant-on, constant-off, and fixed-frequency conditions depending on duty cycle, the resonant period length, and the desired input range.  The method extends the operating range as wide as 12-48V and improves the CEC efficiency to 97.2% in the 250-W prototype.  Chapter 4 considers the soft-start of the proposed system, which can have a very large capacitive load from the inverter.  A new capacitor-transient limited (CTL) soft-start method senses the ac transient across the resonant capacitor, prematurely ending the lower switch on-time in order to prevent an excessive current spike.  A prototype design is then applied to the IBR system, allowing safe system startup with a range of capacitive loads from 2μF to 500μF and a consistent peak current without the need for current sensing.  Chapter 5 further investigates the impact of voltage ripple on the PV output power.  A new method for analyzing the maximum power point tracking (MPPT) efficiency is proposed based on panel-derived models.  From the panel model, an expression demonstrating the MPPT efficiency is derived, along with a ripple "budget" for the harmonic sources.  These ripple sources are then analyzed and suggestions for controlling their contributions are proposed that enable circuit designers to make informed and cost-effective design decisions.  Chapter 6 illustrates how results from a previous iteration can provide a basis for the next generation's design.  A zero-voltage-switching (ZVS) version of the circuit in Chapter 2 is proposed, requiring only two additional MOSFETs and one inductor on the low-voltage side.  The maximum switching frequency is then increased from 70kHz to 170kHz, allowing for a 46% reduction in converter volume (from 430cm³ to 230cm³) while retaining greater than 97% weighted efficiency. / Ph. D.

The duty cycle control (DCC) modulation scheme for the three-phase dual-active-bridge (3p-DAB) DC-DC converter is a promising three degree-of-freedom modulation scheme which can extend the converter’s soft-switching range and reduce conduction losses under partial loading and wide voltage variations. However, the prior suggested methods to implement DCC in 3p-DABs have drawbacks such as requiring a multi-frequency approximation and offline optimization process or achieving less than optimal efficiency. To overcome these challenges, this research first proposes an optimal DCC modulation strategy (OMS) for the 3p-DAB based on a novel piece-wise time-domain analysis (TDA) and optimization process that obtains the optimal control parameters for minimum RMS phase current. Secondly, this research proposes a novel closed-form minimum current stress optimization (MCSO) DCC scheme based on the theoretical findings of the TDA optimization. The MCSO reduces the transformer phase currents and extends soft-switching operation under partial loading and wide voltage variations. Experimental results via open-loop testing show that the proposed closed-form MCSO DCC scheme has virtually identical efficiency as the OMS, making this the first research to provide a closed-form DCC modulation scheme for a 3p-DAB that achieves efficiency results equivalent to a fully-optimized offline scheme, but without the drawbacks of the offline optimization process. / Thesis / Master of Applied Science (MASc)

Electric vehicle (EV) adoption continues to rise, yet EV sales still represent a small portion of vehicle sales in most countries. An expansion of the DC fast charging (DCFC) network is likely to accelerate this revolution towards sustainable transportation, giving drivers more flexible options for charging on longer trips. However, DCFC presents a large load on the grid which can lead to costly grid reinforcements and high monthly operating costs – adding energy storage to the DCFC station can help mitigate these challenges. This thesis first performs a comprehensive review of DCFC stations with energy storage, including motivation, architectures, power electronic converters, and detailed simulation analysis for various charging scenarios. The review is closely tied to current state-of-the-art technologies and covers both academic research contributions and real energy storage projects in operation around the world. It is identified that the battery energy storage systems (BESSs) with active front end converter provides high efficiency with reasonable power density in a DCFC station. It is also realized that the isolated DC/DC converter interfacing BESS and EV determines the overall efficiency of a DCFC station with a low grid connection. Secondly, this thesis analyzes the impact of active front end based DCFC stations connected to a grid distorted with background voltage harmonics. In active front end based DCFC stations, background voltage harmonics produce current not only at the frequencies of the distorted voltage, but also at other coupled frequencies. Various mitigation techniques, such as increasing inner control loop gain, grid voltage feedforward, and selective harmonic compensation, have been adopted in industry to reduce the emissions originating from distorted background voltage. However, although these techniques are effective in suppressing the current at the harmonic orders present in the background voltage, they deteriorate the emission at coupled frequencies. This thesis provides the theoretical explanation of this phenomenon, which is verified by simulation of a two-level active front end in PSCAD/EMTDC. This thesis also discusses the proper treatment of current emission due to background voltage harmonics. Thirdly, the thesis identifies the semi dual active bridge (semi-DAB) converter as an ideal candidate as the interfacing isolated DC/DC converter between the BESS and the BEV. A novel control strategy is proposed for the semi-DAB converter to achieve wide voltage gain while increasing the efficiency at operational points with high input voltage and low output voltage, which is a commonly occurring scenario when the BESS is fully charged, and the EV battery is at low charge. Furthermore, this thesis also provides an algorithm to determine the required phase-shift in real time for any operating point, eliminating the need to devise the control trajectory offline. A 550 V, 10 kW experimental prototype is built and tested to validate the proposed control strategy. With a 25 A constant charging current, the prototype shows the proposed control strategy can improve efficiency by up to 3.5% compared to the well-known dual phase shift control at operating points with high input voltage (450 – 550 V) and low output voltage (150 – 275 V), with a peak efficiency of 97.6%. Finally, this thesis proposes a novel variable turns-ratio semi-DAB converter to improve its overall efficiency even further when the input voltage is high and the output voltage is low. Furthermore, a control law is also proposed to determine the turns-ratio, i.e., the operational structure of the converter, which reduces the converter peak and rms current. The 550 V, 10 kW prototype is modified to accommodate the variable turns-ratio high frequency transformer to test the proposed converter and control. The proposed converter with control can further improve the efficiency at many operating points compared to single turns-ratio semi-DAB with DPS control. The peak efficiency achieved is 98.5%. / Thesis / Doctor of Philosophy (PhD)

Current trends in electronics are toward the use of reduced voltages. In the past, 5 V and higher voltages have been the standard, however, currently, 3.3V and 2.5V circuits are becoming increasingly common. While the operating voltage is decreasing, electronic systems are becoming more complex. The net result is that in many, cases, the current required by the next generation of electronics will be far greater than in the past. These increased currents and low voltages pose dramatic problems for designers not the least of which is the effect of electronic packaging and circuit implementation on the overall power supply performance. In addition, for many applications, space and weight are at a premium and converters are needed to power low voltage circuit assemblies that are highly efficient, low in weight, and small in total height and foot print. This dissertation addresses these trends and needs through the design, fabrication and evaluation of a 3.3V DC/DC converter. Designs of 3.3V, 2.5V, and 1.5V are presented and evaluated while a 3.3V, 100 watt converter with a power density of 157 watts/in³ has been fabricated and evaluated in a miniature form. This converter utilizes a implementation strategy developed by the author which was selected due to its ability to handle the current levels required and its compact size. Specific contributions of this work include: • Analysis of the effects of packaging on low voltage high current converters in order to provide a guideline for converter implementation. This analysis has been performed for 3.3 V, 2.5 V, and 1.5 V designs, respectively. • Development of high efficiency 2.5 V, 100 watt and 1.5 V, 75 watt designs based on previously reported half bridge topologies. • Development of a packaging strategy which allows the fabrication of low voltage compact converters with high efficiency. A 3.3 V converter has been fabricated and with the simulated data validated these experimental results. For very low (less than 50 watts and / or less than 10 amps) and high power levels (hundreds of amps or kilowatts), the implementation strategy is normally clear; PCB/IMS, and DBC respectively. However, for applications in the middle range of power or current level, the optimum implementation is often unclear. The question that this work seeks to answer is under what conditions are different implementation schemes most suitable. / Ph. D.

The demand for high power density, high efficiency bus converters has increased interest in resonant topologies, particularly the LLC resonant converter. LLC resonant converters offer several advantages in efficiency, power density, and hold up time extension capability. Among high voltage (>500V) MOSFETs, Super Junction MOSFETs, such as Infineon's CoolMOS parts, offer lower Rds on than conventional parts and are a natural choice for this application to improve efficiency. However, there is a history of converter failure due to reverse recovery problems with the primary switch's body diode. Before selecting CoolMOS devices for use in a LLC resonant converter, it is necessary to investigate its performance in this application. Field failures of PWM soft switching phase shift full bridge converters have been attributed to large reverse recovery charge in the primary side MOSFET body diode. Under low load conditions the device cannot fully recover, and the large reverse recovery current can cause the device to enter secondary break down, leading to failure. The unique structure of Super Junction MOSFETs, such as CoolMOS, avoid this failure mode by providing a different path for the reverse current; however, the reverse recovery charge of CoolMOS devices is large and can cause a loss of efficiency. For this reason, it is important to avoid conditions under which the reverse recovery characteristics of the body diode can be seen. / Master of Science

In January 1564, Charles IX and Catherine de Médicis embarked on a two-year progress around France. Their motivation was to confirm the authority of the young king and to enforce the Edict of Amboise, which compelled his subjects to show religious toleration following the civil war of 1562-1563. Royal entries were a principal medium through which city councils, on behalf of the people, communicated their views to Charles. As he walked in procession through urban centres, the king was presented with specially-created triumphal arches, paintings and recitals. The imagery in these scenes, which could be illusory or clear-cut, is invaluable when it comes to understanding the interbellum of 1563-1567. This thesis examines the functions and artistic content of these ceremonies, particularly in Troyes, Lyon and Toulouse, in order to reveal how Charles was perceived as a monarch and whether the edict was well-received. The work draws on festival books that detail the scenes, which hitherto have been an untapped resource, and emblem books to elucidate the contemporary meaning behind the images. City council records, local memoirs and correspondence from figures at court have been used to reconstruct the local and national contexts in which the entries were made. This research demonstrates that Charles was viewed as the divinely-chosen ruler to whom complete obedience was owed, but many people had more respect for the office than for Charles himself. They feared he was too young and inexperienced to rule, and this impacted badly on the Edict of Amboise. The Crown had hoped for a peaceful resolution to the conflict and intended the edict as a temporary measure until the heretics returned to the Church or Charles matured into a more inspiring king. Yet the edict was too intolerable to Catholics and Huguenots, particularly among local officials who often obstructed its enforcement, and so peace could not be maintained, even if it was the will of the king.

The subject of this thesis is the Carolingian regnum of Lotharingia in the years between the Treaty of Meersen in 870 and its incorporation into the kingdom of Henry I in 925. Traditionally, the history of this half-century in Lotharingia is told in conventional terms. Despite the loss of its king in 869 and subsequent division in 870, the regnum Lotharii apparently remained a coherent geo-political structure which, in maintaining a permanent presence in the landscape, provided a focus for contemporary political action, and thus a suitable and straightforward topic of subsequent historical investigation. This thesis challenges that traditional approach and demonstrates that, for much of the initial period following 870, the regnum Lotharii was precisely not such a coherent structure. Arguing that standard methodological approaches are flawed in seeing the survival of terminology as evidence of permanence in the political landscape, this thesis offers a more nuanced explanation, and shows that the terminology survived because it provided an elastic political legacy that could be deployed at opportune moments by either kings, or their challengers, in constructing images of their own power and authority. Lotharingia was a politically active unit by the early years of the tenth century and this thesis proceeds to show its emergence. It again exposes traditional explanations as unsatisfactory. This thesis offers an alternative explanation by proposing the emergence of a distinct aristocracy in Lotharingia only at the end of the ninth century. In re-examining the narrative and charter evidence, the thesis reveals this new identity as a reaction to a moment of crisis within the ranks of one particular aristocratic community. It was not a residual identity from an earlier period of political independence waiting for reactivation.

No description available.

This is a study of an event: an abortive royalist insurrection in the city of Nîmes in June 1790 and its aftermath - a series of royalist revolts centred upon the commune of Berrias in the department of the Ardèche in 1790, 1791 and 1792. The thesis is divided into four parts, each designed to contribute to an explanation of what made these events possible. Part I is a discussion of the composition and ideological assumptions of royalism in the South-East of France. Part II consists of an examination of the social and economic structure of Nimes in the eighteenth century. Part III is a study of the relationship between Nimes and its hinterland as it was organised through the production of silk. Part IV deals with the manner in which the form of this town-country relationship intersected with tensions and conflicts within the city itself in the later eighteenth century. It is argued from this analysis that it is impossible to explain royalism in unilateral terms. Royalism was the product of a developing social process; it cannot therefore be deduced from the divisions which it contributed to produce after 1790. Royalists became royalists because of the particular form of their relationship to those who became "patriots" in the decades preceeding 1790. Secondly, royalism cannot be explained exclusively in terms of local and regional tensions. Royalists occupied a particular place within the hierarchy of functions which articulated the relationship between Nimes and its hinterland. Rather, therefore, than deducing royalism from tensions at one particular level - whether of the village, small town, region or city - this study has sought to explain royalism in terms of the relationship between these different levels, and of the manner in which contemporaries sought to understand this relationship. The argument pursued throughout this study is that royalism in the South-East can be seen as one possible "solution" to the "problem" of social mobility in eighteenth century France.

This thesis explores parole detention as a site of transnational exchange through a case study of Verdun, a central depot for British civilian and military prisoners of war in Napoleonic France. By focusing on the interactions between captives and captors, this study throws into relief the ambiguities of nation-building and the totalisation of warfare, which kept these two countries at odds in the long eighteenth century. The main finding that has arisen from this work is the predominance of social dynamics over national, martial and religious antagonisms during this forced cohabitation, which nuances the truism of French and British identities forged against each other during the period. Furthermore, moving beyond the common assumption that the concept of honour lost its substance in France after 1789, I argue that parole detention in Verdun was based on gendered and ad hoc practices of internment, which syncretised old and revolutionary understandings of the notion. Whilst the situation of sequestered women has received little attention, this thesis makes the original claim that parole was in fact tailored to the presence of female 'voluntary captives' in Verdun. Composed of seven thematic chapters, and drawing on a variety of sources (ego-documents, newspapers, botanical specimens, material and visual culture), this thesis intends to provide a fresh sociocultural and transnational contribution to the burgeoning field of POW studies. Beyond conventional and nation-centric 'histoire-batailles', which so frequently place the question of military captivity within the rigid frame of a three-staged 'experience'– a trope inspired by memoirs of captivity – this thesis re-considers the experience of detention as a liminal 'passage'. By putting emphasis less on being than becoming a captive, this perspective situates military detention in a wider temporal framework, which includes the aftermath of 1814 and lifewriting as part of the experience.