Electrical and Electronic Engineering - Theses
Permanent URI for this collection
Search Results
1 - 10 of 278
-
ItemTechno-economic modelling of distributed energy systems and energy communities( 2023-10)Power systems are experiencing an unprecedented transformation, driven by the massive uptake of distributed energy resources (DER) connected to distribution networks. This transformation challenges the traditional configuration of power systems, where large generators supplied energy to passive consumers, and gives rise to a decentralized setup, reshaping power system management and economics. Importantly, this entails that distribution networks, responsible for transporting and delivering electricity to customers, are undergoing a transformation into distributed energy systems, where electricity is consumed, generated, and also stored. As traditionally passive consumers adopt low-carbon technologies like PV systems and Battery Energy Storage Systems (BESS), they become active energy service providers, and increasingly seek opportunities to actively engage with the power system. In this context, energy communities have emerged with promising benefits for consumers, such as lower energy costs, reduced individual investments, and increased self-sufficiency of the community. However, as an emerging concept, the role and responsibilities of energy communities in power systems is unclear, and energy communities face many unanswered questions. Notably, it is yet to be defined if energy communities can balance community objectives, efficiently use the existing network and provide services to the power system, while being economically feasible. The challenges of energy communities are complex and multifaceted, requiring to consider technical, economic, regulatory and commercial aspects. Such comprehensive analysis of energy communities has only been presented in the existing literature qualitatively. This thesis sets out to provide a comprehensive quantitative study of energy communities, developing various techno-economic frameworks including regulatory and commercial aspects, to analyse the operation and investment problems in energy communities. The frameworks developed in this thesis are flexible and comprehensive, allowing to study diverse energy communities with various physical architectures and objectives; adopting various regulatory frameworks and commercial structures including different actors; co-optimizing participation in different markets, system-level and local services; and uncertainty in future local and system-level conditions. The versatility of the proposed frameworks allows to address the most fundamental issues of energy communities, such as if community-level DER provide benefits with respect to privately-owned behind-the-meter DER, as well as propose advancements that can be leveraged by energy communities and, more generally, distributed energy systems, such as the development of a pricing framework for distributed energy markets, and the operational impact of smart grid technologies. Through diverse case studies based on real energy community projects in Australia the potential of the frameworks developed is demonstrated, allowing to provide a novel analysis of energy communities. First, it was found that regulatory frameworks that consider energy communities as a single, independent entity with respect to the various markets and regulated costs results in economically feasible energy communities that also provide operational benefits to the system. Second, regulatory developments should be in place to incentivize distribution system operator engagement with the energy community, allowing energy communities to provide valuable network support services to efficiently manage the network operation, while allowing the energy community to accrue significant revenues. Due to the relevance of local network support, this issue was further explored. First by providing a novel pricing framework for distributed energy markets, sending adequate signals to DER that accurately value the benefits of local network support. Second, by studying the role of smart grid technologies on the provision of local services and their interactions with energy communities and DER.
-
ItemVisible to Mid-Wave Infrared Photodetectors Based on Two-Dimensional Materials( 2023-12)The two-dimensional (2D) materials, such as graphene, are characterised as stable arrangements of atoms bonded via covalent or ionic bonds which form 2D planes (i.e. spanning the x and y direction). In their bulk crystal form, adjacent planes are held together via van der Waals forces (i.e. in the z direction). This is why sometimes they are referred to as the van der Waals materials. They have attracted tremendous attention in recent years as potential candidates for use in next-generation optoelectronic devices due to their tuneable bandgaps, high carrier mobility, high internal quantum yields, strong light-matter interaction, and mechanical flexibility. Among the various 2D materials, transition metal dichalcogenides (TMDCs), graphene (Gr), and black phosphorus (bP) have shown promising properties in the visible to mid-wave infrared (MWIR) spectral range as photodetectors. This is of great interest for applications such as visible/infrared imaging, optical communication, and spectrally sensitive detectors (such as those required for gas sensing). Compared with traditional three-dimensional (3D) compound semiconductor photodetectors, 2D material-based photodetectors have low densities of dangling bonds at their surfaces, strong light-matter interaction, and low thermal noise, which provides fundamental advantages in terms of signal-to-noise performance, particularly in infrared photodetection. In addition, the weak van der Waals forces holding planes together allow easy cleavage and assembly of 2D material heterojunctions as well as transferal onto established microelectronics platforms (such as silicon complementary metal-oxide-semiconductor chips). In this thesis, I present the design, fabrication, characterization, and modelling of photodetectors based on 2D materials in the vis to MWIR region. In the introduction chapters, I first discuss the basic concepts and principles of photodetection and 2D materials, and then review the state-of-the-art developments in this field. Following this I describe the experimental methods and techniques used in our work, including device fabrication, as well as materials and photodetector performance characterisation. In the first experimental chapter, I report our experimental results on the first demonstration of photodetectors based on ZrGeTe4, a new van der Waals material with a narrow bandgap in the SWIR region. I describe the device fabrication and characterisation of ZrGeTe4 based photodetectors and evaluate its performance as a photodetector under different conditions. I investigate the stability of ZrGeTe4 and prove that ZrGeTe4 is a promising candidate for stable, high-performance optoelectronic devices operating at room temperature in the SWIR region. The potential application of ZrGeTe4 as a position-sensitive lateral detector due to its asymmetric photocurrent. I demonstrate simple proof-of-concept broad spectrum photodetectors responsivities above 0.1 A W-1 across both the visible and short-wave infrared wavelengths. This corresponds to a specific detectivity of ~10 9 Jones at 1400 nm at room temperature. These devices show linearity in photoresponse over ~4 orders of magnitude and a fast response time of ~50 ns. As the first demonstration of photodetection using ZrGeTe4, these characteristics, measured on a simple proof-of-concept device without significant optimization, shows the exciting potential of ZrGeTe4 for room temperature IR optoelectronic applications. In the following chapter, I present a Fabry-Perot cavity enhanced bP MoS2 photodiode. I demonstrate the fabrication process and the optical structure of the device, which consists of a bP MoS2 heterojunction embedded in a Fabry-Perot cavity with two symmetrical dielectric/metal mirrors and claim that this device has promising potential for IR spectroscopic applications, such as gas sensing and imaging. This simple structure enables tunable narrow-band (down to 420 nm full-width-half-maximum) photodetection in the 2000 to 4000 nm range by adjusting the thickness of the Fabry-Perot cavity resonator. This is achieved whilst maintaining room temperature performance metrics comparable to previously reported 2D MWIR detectors. Zero bias specific detectivity and responsivity values of up to 1.7x10 9 Jones and 0.11 A W-1 at 3000 nm are measured, with a response time of less than 3 ns. These results introduce a promising family of 2D detectors with applications in MWIR spectroscopy. In the last experimental chapter, I fabricate a dual-gate pn junction photodiode by electrostatic doping. The hBN-bP-hBN dual-gate devices were fabricated and trialled for IR light collection/detection. It is shown that applying sufficiently large bias to one of the two rear gates, whilst holding the other at zero bias, leads to the formation of a lateral pn junction. Under IR illumination, this lateral pn junction exhibits the photovoltaic effect yielding a VOC as high as 175 mV and 74 mV, at 77 K and 295 K, respectively. These are the highest values reported for bP based dual-gate devices to date. When being used to detect light, under zero source-drain voltage, a specific detectivity of 8.5x10 8 and 2x10 7 Jones is measured at 77 K and 295 K, respectively. By modulating the back gate voltage, the dual-gate structure also allows switching between photoconductive and photovoltaic modes of operation. This allows a trade-off between low noise/fast response (photovoltaic mode) and high responsivity (photoconductive mode). Further, it is shown that the device can also be operated in a photoconductive mode of operation allowing a high responsivity of 0.55 A W-1 (VDS = -500 mV, 77 K). This development extends the application of dual-gate van der Waals materials photodetectors into the IR wavelength space. In the final chapter of this thesis, I summarise our main findings and contributions, and suggest some future directions and challenges for this research area.
-
ItemNo Preview AvailableA Multifunctional Smart Field-Programmable Radio Frequency Surface( 2023-04)Wireless communication technology has completely transformed the way we communicate and access information. It operates on the principles of electromagnetic wave propagation, as described by Maxwell's equations. The scope of wireless communication is vast and includes satellite communication, handheld device communication, and Internet of Things (IoT), which have revolutionized fields of industry, healthcare, transportation, education, and entertainment. As demand for faster and more reliable communication continues to grow, a range of wireless communication standards has been developed, including WiFi, BLE, cellular networks, near-field communication (NFC), and ZigBee, each operating at a unique frequency range. Antennas that can operate across multiple communication standards have remained a challenge due to the interdependent factors of antenna geometry, size, and RF characteristics. As the number of devices with wireless connectivity increases dramatically, the spectrum resource is getting limited, which results in congestion and reduced performance. Reconfigurable antennas have been intensively studied in the last few decades to mitigate this challenge. Although reconfigurability in operating frequency, radiation pattern and polarization have been implemented, limitations including lack of programmability, pattern diversity, and self-adaptive capability against environmental interference exist. To address these limitations, we proposed a new concept called Field-programmable RF surface (FPRFS), which allows for the control of current flow on the surface to achieve desired antenna characteristics and impedance matching capabilities. This work starts with the theoretical analysis and creates the mathematical model for the FPRFS in antenna, impedance matching network, and filter applications. Our research demonstrated the reconfigurability of FPRFS antennas in operating frequency, radiation pattern, and polarization reconfigurability with radiation gain and efficiency levels that are comparable to those of conventional fixed patch antennas and enhanced immunity to surrounding obstacles. We developed a software algorithm for the FPRFS that enables it to automatically optimize its configuration in real-time, thereby adapting to changing load impedance or environmental interferences.
-
ItemPolarization effects and high speed transmission in coherent optical OFDM systems(University of Melbourne, 2010)
-
ItemBiological learning mechanisms in spiking neuronal networks(University of Melbourne, 2009)
-
ItemDesign and implementation of millimeter-wave transceivers on CMOS(University of Melbourne, 2008)
-
ItemMillimeter wave CMOS VCO and PLL design and phase noise mitigation techniques(University of Melbourne, 2008)
-
ItemNovel all-optical signal processing schemes and their applications in packet switching in core networks(University of Melbourne, 2007)
-
ItemSteady-state multi-energy flow problem in coupled energy networks( 2023-07)Energy systems worldwide are experiencing a rapid transition towards a low-carbon future, calling for greater energy efficiency and flexibility in utilising energy networks. This transition is accompanied by the growing adoption of multi-energy technologies like combined heat and power (CHP), power-to-heat, and power-to-gas units, leading to rising interdependencies between different energy networks, particularly in district and energy community applications. Hence, more effective utilisation of coupled energy networks (CEN) can bring several efficiency and flexibility benefits. Developing efficient energy flow models for CEN analysis is thus key to fully unlock these inherent benefits. The steady-state multi-energy flow (MEF) problem is the cornerstone of CEN analysis and lays the foundation for optimal operation and flexibility studies. This thesis presents a systematic evaluation of the MEF problem for steady-state analysis of CEN, exemplified in the case of coupled electricity, heat, and gas networks, by highlighting three main principles, namely formulations, coupling strategies, and solution techniques. Regarding formulations, a MEF framework is developed to incorporate various formulations for steady-state analysis of CEN, while demonstrating their impact on the convergence and computational properties of MEF models. With respect to coupling strategies, a systematic analysis is conducted on three essential coupling strategies, i.e., Decoupled, Decomposed, and Integrated, which may be associated with parallel, sequential, and simultaneous MEF computations, respectively. A set of fundamental underlying principles that characterise the coupling effectiveness in the MEF problem is introduced, namely, underlying formulations, problem size, interdependencies between networks, and calculation sequence, while highlighting their role in appraising different coupling strategies. In terms of solution techniques, besides classical Newtown-Raphson (NR), the performance of other potentially suitable algorithms, such as Quasi-NR, Levenberg-Marquardt, and Trust-Region, is extensively studied for solving MEF problems. A novel cross-over strategy is then proposed to utilise the synergistic benefits of studied algorithms for improving convergence properties without compromising computational efficiency. Building upon the insights gained from the MEF analysis, a fast decomposed algorithm is introduced for solving large-scale coupled electricity and gas networks with hydrogen injection modelling and gas composition tracking. Finally, this thesis provides novel insights and practical recommendations to identify the most suitable formulations, coupling strategies, and solution techniques for solving the steady-state MEF problem in a robust and computationally efficient way.
-
ItemCommunication Receivers with Low-Resolution Quantization: Fundamental Limits and Task-based Designs( 2023-08)The use of low-resolution analog-to-digital converters (ADCs) in communication receivers has gained significant interest in the research community since it addresses practical issues in 5G/6G deployment such as massive data processing, high power consumption, and high manufacturing cost. An ADC equipped in communication receivers is often designed such that its quantization thresholds are equally-spaced or the distortion between its input and output is minimized. These design approaches, however, may yield suboptimal performance as they neglect the underlying system task that the ADCs are intended to be used for. This presents an opportunity for us to explore receiver quantization designs that cater to specific communication tasks (e.g. symbol detection, channel estimation) and to understand how quantization impacts various aspects of receiver performance such as error rate, channel capacity, estimation error. In this thesis, we consider five independent research problems related to the communication receivers with low-resolution quantizers. Three of these research problems deal with capacity analysis of certain communication channels with quantized outputs. More precisely, we derive the capacity-achieving input distributions for four different channels with phase-quantized observations and the Gaussian channel with polar-quantized observations. For the channels with b-bit phase quantizer at the output, 2^b-phase shift keying modulation scheme can attain the channel capacity. Meanwhile, the capacity can be achieved in the Gaussian channel with polar quantization by an input distribution with amplitude phase shift keying structure. Capacity bounds for MIMO Gaussian channel with analog combiner and 1-bit sign quantizers are also established in this thesis. The remaining two research problems fall under the category of task-based quantizer design. The idea is to design the quantizer in accordance to the underlying system task rather than simply minimize its input-output distortion. Focusing on M-ary pulse amplitude modulation (PAM) receiver with symmetric scalar quantizer, the closed-form expression of the symbol error rate is derived as a function of quantizer structure and position of equiprobable PAM symbols. The derived expression is used to design the quantizer according to the symbol detection task. The high signal-to-noise ratio (SNR) behavior of the error rate of the quantized communication system is characterized. Our final work is a development of a new design and analysis framework for task-based quantizers with hybrid analog-to-digital architecture. In contrast to existing task-based quantization frameworks, the theoretical predictions of our proposed framework perfectly coincides with the simulated results. Moreover, the proposed frameworks can be used in data acquisition systems with non-uniform quantizers and observations with unbounded support.