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    A Scalable Virtual Zonal Aggregation Framework for EV Charging Coordination and Transformer Overload Prevention in Residential Distribution Networks
    (University of Waterloo, 2026-08-26) Fahad, Abul Hasan
    The accelerating adoption of electric vehicles (EVs) is transforming residential electricity demand in ways that traditional low-voltage distribution networks were never designed to accommodate. Coincident, uncoordinated EV charging produces large, synchronised load peaks that regularly push residential distribution transformers beyond their thermal ratings — accelerating insulation aging, threatening voltage stability, and increasing the risk of unplanned outages. Existing coordination frameworks address this challenge imperfectly. Centralised approaches operated by a Distribution System Operator require direct control of customer assets and face prohibitive computational burdens at scale. Decentralised peer-to-peer schemes preserve customer autonomy but provide no mechanism to enforce a binding physical capacity constraint at the transformer level. Neither paradigm offers a market-compatible mechanism that simultaneously protects the transformer, reduces customer electricity costs, and sustains the coordinating intermediary without external subsidy. This thesis introduces a Virtual Zonal Aggregation (VZA) framework designed to fill that gap. The architecture partitions a distribution feeder into virtual zones, each administered by a cloud-hosted Virtual Zonal Aggregator (VZA) that coordinates one or more Virtual Transformers — software digital twins of physical distribution transformers — within its zone. The VZA sets day-ahead retail price signals derived from wholesale market prices and iteratively refines them; each Virtual Transformer enforces its own transformer's thermal capacity limit by aggregating the load profiles of its downstream customers and detecting overloaded hours. Customer Home Energy Management Systems (HEMS) respond to these signals by solving individual cost-minimisation problems and returning updated load profiles. No direct load control is imposed; customers retain full autonomy over their EV charging decisions. When the aggregated load in a zone exceeds a transformer's thermal limit, the Virtual Transformer reports the overload to the VZA, which initiates an iterative price-update loop — increasing prices in overloaded hours and reducing them in underloaded ones — until the load profile becomes feasible. The framework is validated through a simulation case study on a 15-customer residential feeder served by a single distribution transformer, using real Hourly Ontario Energy Price (HOEP) wholesale data and seasonal baseload profiles derived from 18 months of anonymised smart-meter data provided by Toronto Hydro. Under the Ontario Time-of-Use (TOU) baseline (Scenario A), uncoordinated EV charging causes transformer overloads in both winter and summer. The VZA framework (Scenario B) eliminates all overloads in 6 iterations (winter) and 15 iterations (summer) through iterative price-signal updates, while simultaneously delivering a 43.4% reduction in community net electricity cost in winter and a 58.3% reduction in summer — with every individual customer benefiting. The Virtual Zonal Aggregator sustains a daily profit of $10.15 (winter) and $11.87 (summer), confirming economic viability without external subsidy or direct load curtailment. The scalability and safety of the framework beyond the single-zone case study are established through seven formal results derived for standard IEEE radial distribution test feeders and presented in Chapter 3. A zone independence proposition proves that in any radial network each Virtual Transformer's overload sub-problem is fully decoupled from every other zone by Kirchhoff's current law, so the multi-zone coordination problem decomposes into N independent parallel sub-problems. A voltage stability proposition proves that enforcing the per-transformer kW ceiling simultaneously guarantees an analytical lower bound on all bus voltages satisfying the ANSI C84.1 Range A service requirement (≥ 0.95 p.u.), validated numerically on the IEEE 33-bus feeder via linearised DistFlow under standard unity-PF EV and bounded-reactive-load assumptions. A zone feasibility proposition derives a necessary and sufficient condition — relating the transformer's 24-hour load headroom to the zone's aggregate EV energy demand — under which an overload-free schedule is guaranteed to exist. A finite convergence proposition proves that the iterative price-update algorithm eliminates all overloads in a finite number of iterations; a network-wide corollary extends this to N parallel zones. A system non-disruption proposition establishes that the algorithm is operationally conservative at every intermediate iteration: it preserves each customer's full daily energy requirement, reduces total transformer overload monotonically at each step, and keeps retail prices within operator-set bounds throughout. Beyond these qualitative guarantees, a geometric overload reduction theorem sharpens the convergence result to a quantitative rate: the total overload energy contracts geometrically by factor (1 − c) per iteration, where the contraction constant c ∈ (0, 1) is derived entirely from physical system parameters and algorithm design choices, giving an explicit closed-form iteration bound K*. A counter-intuitive implication is that larger zones converge at least as fast as smaller ones, because aggregate EV flexibility grows with zone size while the transformer limit is fixed. A horizontal scalability theorem proves that adding zones to the network does not increase the iteration count for any existing zone and that total wall-clock time scales as O(K* · Mmax), independent of the number of zones. Together, these results place the single-zone empirical study on a rigorous quantitative theoretical footing and guarantee that the architecture composes to networks of arbitrary size at no additional algorithmic cost.
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    Graduate Student Perceptions of Food Security in Kitchener-Waterloo Region
    (University of Waterloo, 2026-08-26) Rauch-Davis, William
    This thesis examines the experiences of graduate students accessing food while attending the University of Waterloo. Food insecurity among post-secondary students has become an increasing concern in Canada, with students experiencing food insecurity at rates often higher than the national average. While university food insecurity has been studied, much of the existing literature focuses on undergraduate students or treats university students as a homogenous population. The purpose of this study is to explore how and where University of Waterloo graduate students access food in Kitchener-Waterloo and whether the food they do access reflects their individual needs This thesis adopts the Four Pillars of Food Security framework which includes availability, accessibility, utility, and stability. A mixed-methods approach was used to conduct this research. Data collection included an online questionnaire distributed to graduate students at the University of Waterloo (n=133) and semi-structured interviews with graduate students (n=20). A thematic analysis was used to identify recurring themes across the data. The findings demonstrate that affordability is one of the most significant barriers influencing the ability of graduate students in the study sample to access food. Rising housing costs, limited funding, and financial instability often forced students to make trade-offs between food and other necessities.. International students and students with dietary restrictions reported difficulties with unfamiliar food environments and accessing foods that meet their cultural or dietary needs. Participants described a variety of coping strategies including budgeting, meal planning, attending events with free food, and accessing community or campus food resources. However, many participants also described feelings of stress, guilt, and stigma associated with food or seeking assistance. The research further highlights the importance of institutional responsibility in shaping campus food systems and ensuring that food initiatives reflect the diverse needs of graduate students. Overall, this thesis contributes to the growing body of literature on student food insecurity by centering the experiences of graduate students and situating these experiences within broader structural contexts. Policy interventions to support these findings include strengthening partnerships with community food organizations, retailers, and local producers. These policies can give graduate students more autonomy over their food choices and help to provide skills that can extend beyond their university experience. The findings emphasize that food insecurity among graduate students is not an individual issue, but one shaped by economic pressures, campus food environments, and broader systems.
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    Finite-Size Orientational Crossover in Water–Argon Chains with Optional Carbon Nanotube Confinement
    (University of Waterloo, 2026-08-25) Dass, Ajay
    Nanoscale confinement can strongly alter the orientational behaviour of water. This thesis investigates whether local axial orientation persists when neighbouring water molecules are separated by fixed argon atoms, and how optional confinement within a (6, 5) carbon nanotube modifies that response. Finite water–argon chains were modelled as fixed-centre asymmetric-top water rotors with stationary argon spacers and nearest-neighbour water–water interactions. Ground states were calculated using the density-matrix renormalization group in a matrix product state representation as the water–water separation, R, was varied. The analysis combined energy, central von Neumann entropy, signed and absolute axial orientation, site-resolved profiles, angular distributions, and numerical convergence diagnostics. The principal result is a finite-size orientational crossover obtained for the ordinary open-boundary finite-chain Hamiltonian. The sampled central-entropy maximum moves to larger R with increasing chain length and approaches the 9–10 Å region for the larger chains. In the same main crossover window, the signed mean axial orientation is strongly reduced while the mean absolute local orientation remains appreciable. Site-resolved results show that differently biased parts of the chain make cancelling contributions while local axial orientation remains. The ground-state energy per water varies smoothly and has no corresponding feature. CNT confinement shifts and modestly suppresses the sampled entropy response, while the matched orientation curves remain similar over most of the main crossover window. CNT OFF and CNT ON are therefore consistent with the same general response, although an identical microscopic mechanism is not established. The separate short-R boundary-sensitive feature near R ≈ 7 Å was examined over R = 6.80–7.30 Å using sine-square deformation. Its entropy and branch-selection patterns change under SSD, showing sensitivity to boundary weighting without isolating an individual boundary contribution. This dataset does not test the boundary robustness of the finite-size orientational crossover. The conclusions apply to ground states of the finite, fixed-centre, nearest-neighbour Hamiltonian and do not establish a thermodynamic phase transition or physical excitation gaps.
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    Re-examining Contribution Fairness in Federated Learning
    (University of Waterloo, 2026-08-25) Costa Campos, Guilherme
    Federated Learning (FL) allows multiple data owners to train a shared model collaboratively without exposing their local datasets. Because participation imposes real computation, communication, and data-collection costs, sustaining long-term collaboration requires reward mechanisms that satisfy contribution fairness, the principle that each client should be rewarded commensurately with its contribution to the training. A substantial body of research pursues this goal through the distribution of contribution-based Top-K sparsified gradient rewards, such that higher-contributing clients receive denser, and, therefore, more useful, gradients than lower-contributing ones. Top-K sparsification, however, was originally devised as a gradient-compression technique intended to preserve convergence, which raises the question of whether it can actually produce the client-level model differentiation that contribution fairness demands. Furthermore, existing frameworks often combine distinct contribution estimation algorithms, reward generation rules, and client model update methods, making it unclear which component is responsible for the observed fairness behavior. This thesis investigates these questions by implementing two representative state-of-the-art frameworks, namely ACGSV and CFFL, and evaluating them across four benchmark datasets under distinct training-data partition settings. Building on this comparative evaluation, a series of controlled ablation studies is conducted to isolate the effects of three key components: the gradient used for reward generation, Top-K sparsification, and the retention of each client's locally accumulated gradient. The analysis yields three main findings. First, contribution fairness is commonly evaluated using Pearson’s r between clients’ standalone and federated test accuracies, with standalone accuracy serving as the reference contribution value and forming a set of contribution ranks. However, Pearson's r can remain high even when most clients converge to nearly identical federated accuracies and the reference contribution ranking is not preserved. Thus, Pearson’s r alone may provide an incomplete fairness assessment. To address this limitation, this thesis proposes a novel protocol that uses Kendall’s τ to measure the reference contribution ranks preservation and the Gini Mean Difference to quantify differentiation among the final client models. Second, Top-K sparsification induces significant model differentiation primarily when reward sparsity is high, corresponding to at least 70% in the studied settings. At lower sparsity levels, clients tend to converge to models with nearly identical performance. These findings indicate that sparsifying the aggregated gradient through Top-K is not, by itself, an effective and calibrated mechanism for estimated-contribution-based reward allocation. Third, local gradient retention, whereby clients retain their locally accumulated gradients generated during model training alongside the received estimated-contribution-based reward, is commonly treated as a secondary detail in framework design because it is not governed by the FL framework's contribution estimation algorithm and the contribution-score-to-reward mapping pipeline. However, it is an under-acknowledged confounding factor that drives much of the model differentiation, preservation of the reference contribution ranking, and, consequently, the high fairness scores reported by these frameworks.
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    Polymer-Integrated Halide Perovskite Solar Cells and Photoelectrochemical Cells for Solar Energy Conversion
    (University of Waterloo, 2026-08-25) Khamgaonkar, Saikiran
    Energy demand is skyrocketing, which has led to excessive use of non-renewable resources such as fossil fuels, which are major contributors to climate change and global warming. Therefore, to meet the increased energy demand while reducing carbon footprints, the implementation of renewable technologies for the production of clean energy is needed. In this context, the utilization of solar energy is one of the most appealing strategies for clean energy production. In recent years, halide perovskite solar cells and photoelectrochemical cells have emerged as potential candidates for harvesting solar energy into electricity or storing it directly as chemical fuels. This is mainly due to their excellent optoelectronic properties, along with simple, low-cost solution processing. Although high efficiencies have been achieved for both devices, their long-term stability remains one of the major issues that impedes their commercial deployment. In this thesis, the stability challenge of halide perovskite devices are addressed by implementing polymeric passivators to improve both extrinsic and intrinsic stability. Additionally, novel electrocatalysts have been designed and successfully integrated with these passivated perovskite devices to develop efficient and stable photoelectrochemical cells for green hydrogen production. In Part A, Chapter 2, we focus on simultaneously passivating both bulk and interfacial defects present in perovskite thin films using polystyrene as a bulk additive along with 4-fluorophenethylammonium iodide as the interfacial passivating agent. The addition of polystyrene modulates the perovskite crystallization kinetics, leading to the formation of larger grains with fewer grain boundaries. Meanwhile, 4-fluorophenethylammonium iodide passivates surface defects such as undercoordinated Pb²⁺ sites and vacancies. This combined passivation leads to perovskite solar cells with a high efficiency of 22.4%, along with significant improvement in stability, retaining 92% and 99% of their initial efficiency after 1008 h and 560 h under ISOS-D-1 and ISOS-D-2 conditions, respectively. Part A, Chapter 3 focuses on addressing thermal instability challenges in perovskite solar cells. Most high-efficiency halide perovskite compositions consist of either MA as an A-site cation or as an additive to stabilize the alpha phase of the perovskite. The addition of MA⁺ cations, even in small amounts, can lead to thermal instability due to their volatile nature. In this work, a dipolar polymeric passivator is developed by systematically modulating the electronic structure of polystyrene. A novel poly(pentafluoropolystyrene) passivator is identified, which consists of a distinct electronic distribution with highly diffused electron-rich and electron-deficient regions. These regions not only passivate both cationic and anionic defects in the bulk and at the surface of the perovskite but also exhibit strong interactions with MA⁺ species. This results in perovskite solar cells with efficiencies as high as 24%, along with significant improvement in thermal stability, retaining 95% of the initial efficiency after 2000 h under ISOS-D-2 conditions. Additionally, the storage and operational stability of the devices are greatly improved, retaining 97% and 95% of their initial efficiency after 3500 h and 500 h under ISOS-D-1 and ISOS-L-1 testing conditions, respectively. In Part B, Chapter 4, polystyrene bulk-passivated perovskite solar cells are integrated with bimetallic catalysts to fabricate perovskite photocathodes for green hydrogen production. Here, polystyrene is incorporated into the bulk of the perovskite to improve the intrinsic stability of the solar cells against ion migration. Additionally, using a facile self-assembly process of Au nanoparticles, a bimetallic Au–Pt–Ni catalyst is designed, which shows low overpotential and fast kinetics for the hydrogen evolution reaction in both acidic and basic conditions. The polymer-incorporated photocathodes show excellent performance with a half-cell solar-to-hydrogen (HC-STH) efficiency of 10.11%, along with significant improvement in stability, with T₈₀ values of 70 h (in H₂SO₄) and 78 h (in KOH), indicating improved device lifetime. In Part B, Chapter 5, highly efficient and stable bias-free water splitting is achieved by developing a polymer integrated perovskite photoelectrochemical cell. In this work, two critical challenges of PEC cells are addressed: (a) intrinsic instability of perovskite solar cells under external bias and (b) sluggish catalyst performance. Improved intrinsic stability against ion migration is achieved by implementing 4-fluoropolystyrene as both bulk and interfacial passivating agent. Meanwhile, an Au–Pt–Ni–PBA bifunctional catalyst is developed which shows low overpotential and fast kinetics for both hydrogen and oxygen evolution reactions. These combined effects lead to the fabrication of polymer-incorporated perovskite-based photocathodes with half-cell STH efficiencies of 18.6% and photoanodes with applied bias photon-to-current efficiency of 12.7%, along with excellent stability. Most impressively, the polymer-incorporated photoanodes maintain 95% of their initial performance after 270 h of operation under external bias. This improvement is primarily attributed to the incorporation of the polymer, which significantly reduces ion migration under applied bias conditions. Finally, the combined photoelectrodes enable unassisted water splitting with an STH efficiency of 13.56% and a T₉₀ of 190 h. Therefore, this work highlights the importance of improving the intrinsic stability of perovskites under external bias, along with efficient catalyst engineering.