Electrical and Electronic Engineering - Theses
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ItemPolarization effects and high speed transmission in coherent optical OFDM systems(University of Melbourne, 2010)
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ItemBiological learning mechanisms in spiking neuronal networks(University of Melbourne, 2009)
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ItemDesign and implementation of millimeter-wave transceivers on CMOS(University of Melbourne, 2008)
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ItemMillimeter wave CMOS VCO and PLL design and phase noise mitigation techniques(University of Melbourne, 2008)
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ItemNovel all-optical signal processing schemes and their applications in packet switching in core networks(University of Melbourne, 2007)
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ItemResource allocation for multiuser OFDM systems(University of Melbourne, 2006)
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ItemA Modelling Framework for Virtual Power Plants Under Uncertainty( 2021)The increased integration of renewable energy sources (RES) and distributed energy resources (DER) into electrical networks is causing operational challenges. The reduction in conventional generators, which would traditional provide the reliability and security services for electrical networks, means that these services must now be supplied by other resources. Simultaneously, the intermittency of RES and the lack of visibility of DER means that in some cases these services are required more frequently to maintain a reliable electrical grid. If RES and DER are aggregated and properly controlled in a virtual power plant (VPP) they have the potential to provide network services as well as increase their profitability. The operation of a VPP is a complex problem. While this problem has been examined by numerous authors, no operating framework has been previously proposed that includes consideration of: participation in multiple markets; provision of network and contractual services; modelling of network power flows and voltages; interactions between multiple energy vectors; uncertainty in operational forecasts and; tractability for short dispatch periods. These are key properties for a comprehensive framework that fully captures and unlocks the potential of a VPP. This thesis presents the design and application of a VPP operational framework that incorporates these six key properties. This optimisation-based framework is decomposed into three optimisations to integrate these properties in a tractable manner. This framework is applied to various realistic case studies to prove the efficacy of the proposed approach. The application of this framework demonstrates that the combination of scenario-based optimisation and receding horizon control used is effective at mitigating the effects of uncertainty. The inclusion of short dispatch periods is shown to be key for revenue generation in markets with short dispatch windows. In addition, the application of this framework demonstrates the ability of a VPP to participate in multiple markets and services, and that doing so is essential for maximising VPP revenue. Moreover, the integration of hydrogen resources into the electrical grid provides flexibility that can be assigned to various markets and services. Furthermore, operating in multiple markets fundamentally changes the operational strategy of hydrogen resources, and can increase the amount of hydrogen that can be profitably generated. Additionally, the convex relaxation used for the dispatch of resources is sufficiently accurate to allow a VPP to maintain a network within allowable limits whilst maintaining problem tractability. Lastly, the framework is versatile enough to be utilised by other entities (such as a distribution system operator), or for different purposed (such as techno-economic analysis for business case assessments).
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ItemDistributed multi-agent decision-making for task assignment and collision avoidance( 2021)Multi-agent systems generally involve agents cooperating or coordinating to perform complex tasks. Typically, agents must do so by computing decisions amongst themselves without a centralised decision-maker. In this thesis, a team of agents with different initial locations is tasked with shifting their positions to a set of goal locations. There are two aspects of this type of multi-agent mission that are of interest. The first relates to deciding which agent to assign to which goal location. The second aspect relates to deciding how the agents should move to their goals without colliding with each other along the way. These two aspects can be investigated separately but they are also linked as assigning agents in particular ways can lead to intrinsic collision avoidance between agents. This thesis explores each of these ideas. Assignment problems arise in multi-agent systems when there is a need to allocate a set of tasks to a set of agents. Two types of assignment problems are considered in this thesis. The Bottleneck Assignment Problem (BAP) is an assignment problem where the objective is to minimise the costliest allocation of a task to an agent, while the Lexicographic Bottleneck Assignment Problem (LexBAP) is a related problem with the objective of further minimising the allocation costs of the remaining agents and tasks. These two types of assignment problems are highly applicable in time-critical applications, where there is a need for agents to complete tasks such that the worst-case completion time is minimised. Hence, many centralised algorithms exist to solve them. However, it has become increasingly desirable to produce solutions without relying on a centralised decision-maker. In particular, there is a need for distributed algorithms to solve these problems that do not require a centralised decision-maker having access to all information from each agent. Distributed algorithms for assignment problems with other objectives have been proposed, yet to date no such algorithms for either the BAP or the LexBAP exist. In order to address this gap, novel tools for analysing the BAP and LexBAP are introduced. The introduction of these tools precipitates an analysis of structure in the BAP, where in particular, an investigation into how two separate BAPs can be merged into a combined BAP is conducted. Then by applying these concepts, a distributed algorithm for the BAP is presented, a greedy distributed algorithm for the LexBAP is developed and conditions on exactness of the greedy approach are provided. Numerical results are presented for both distributed algorithms to benchmark them against existing approaches. In specific applications where agents are mobile robots that move towards goal locations to complete tasks, it is subsequently prudent to guarantee inter-agent collision avoidance once the assignment problem is computed. Two approaches for providing collision avoidance guarantees are explored. The first approach shows collision avoidance as an intrinsic property of assigning agents according to the LexBAP, which leads to time-varying safe sets of positions for agents. The second approach considers the use of Control Barrier Functions for collision avoidance, which alternatively leads to time-varying safe sets of accelerations for mobile agents modelled as double integrators.
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ItemMulti-service Supply Adequacy Assessment Framework in Renewables - Dominated Power System( 2021)Many challenges have emerged as the penetration of renewables keeps increasing during the low-carbon transition of power system, among which the most fundamental one could be maintaining power system reliability. In conventional system planning exercises, only system adequacy is considered as the criteria to guarantee reliability. However, the conventional system adequacy concept may not guarantee system reliability anymore due to several challenges brought by the increasing penetration of renewables. Those challenges mainly include concerns about system flexibility issue, as well as system resilience issue considering the wind or solar scarcity for days or weeks. Furthermore, the increasing uptake of distributed energy resources (DER) has also brought great challenges to system reliability and resilience planning due to their various operation paradigms. There are many and far-reaching consequences of planning decisions towards a RES-dominated power system, most notably in terms of system reliability and resilience. When it comes to supply reliability and resilience, there is a vibrant interplay between renewable energy resources (RES), transmission networks, and storage in the context of RES integration and their enabling assets. As the penetration of RES keeps increasing, where large-scale wind and solar farm as well as roof-top PV have accounted for the majority of RES installation capacity, it will be critical to determine the role of different types of storage in supporting system reliability (as well as system resilience to extreme events) coordinating with RES at both transmission and distribution levels. A systematic framework is developed for evaluating the contribution of RES and EES to the adequacy, flexibility, and resilience of RES-dominated system generation. The ability of the system to procure sufficient generation and transmission facilities to support system adequacy, flexibility and resilience is referred as the “multi-service supply adequacy” in this work. Additionally, this thesis has performed a thorough cost-benefit analysis of the effects of distributed energy storage (DES) on enhancing the reliability and resilience of both the distribution community (with a specific focus on rural area communities) and the bulk transmission system. Further, the relationship between electrical energy storage (EES) investment and system reliability and resilience performance is clearly illustrated and explained.
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ItemSystem dynamics of low-carbon grids: fundamentals, challenges, and mitigation solutions( 2021)Going towards low-carbon grids results in massive grid integration of converter-interfaced technologies and its consequent phase-out of synchronous generators, which could potentially threaten system frequency stability/resilience, associated with low-inertia conditions and inadequate frequency control ancillary services, and voltage stability/control, associated with low system strength and weak-grids. Therefore, system operators need to figure out alternative solutions to provide system dynamic supports of various types (i.e., voltage/reactive power and frequency/active power supports) in order to guarantee a stable and secure system operation. This requires a deep understanding of the dynamics of low-carbon grids, as well as the emerging converter-based technologies, under weak and low-inertia conditions. This thesis presents the principles of low-carbon grid dynamics and the modelling foundations for converter-based resources of various types, i.e., battery, electrolyzer, and photovoltaics, to study their potential benefits and challenges in system dynamic supports. Regarding large-scale batteries, their actual capabilities in multiple dynamic supports are discussed while highlighting the technical challenges/interactions associated with low system strength and frequency-dependent protection schemes. Also, the impacts of reactive power prioritization on the battery converter stability, as well as the external system voltage stability, are studied while highlighting the necessity of specific control design requirements and response characteristics at weak distribution/transmission connections. With respect to hydrogen electrolyzers, the proposed detailed dynamic model takes into account electrolysis stack thermodynamics, power-electronics interface, converter control loops, and operational constraints in hydrogen production. The proposed model is then suitable to study the potential capabilities/challenges of electrolysis units in frequency control. Regarding photovoltaics dynamic modelling, a dynamic equivalent model is proposed based on a novel closed-loop system identification approach. The proposed dynamic equivalencing approach is able to capture with good fidelity the aggregate frequency response from solar units while reducing the complexity in combined transmission-distribution frequency response analysis. The potential stability and resilience benefits from the mentioned resources, and the role of different design setups and operational conditions/requirements, are studied following credible and non-credible extreme events in the context of realistic Australian case studies.