3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Investigating the feasibilty of deploying scalable AD-HOC DG microgrids for rural electrification through hardware and software techniques(2018) Iradukunda, Didier JohnThis dissertation investigates the technical feasibility of deploying scalable hybrid DC picogrid systems for rural off-grid areas, by assessing the technical (hardware and software) requirements for implementing a minimal (12V, 100W nominal), laboratory prototype of such a system. The laboratory prototype validates the proposed concept of an ad-hoc localised low-voltage DC grid (“Picogrid”) as a resilient and robust solution for off-grid electrification at low power levels. It demonstrates the scalability, fault tolerance and other features which are required for the intended application. Existing off-grid low voltage DC systems (like the solar home systems) cannot be scaled up in terms of power increase, load expansion or storage extension and this severely limits the usability of the available systems. The “Picogrid” concept put forward here is one of the possible solutions that can be scaled in every dimension (generation, storage and load) by having multiple autonomous sources and storage nodes networked together in an Ad-Hoc manner. Stable operation is achieved by a global grid code defining each node’s action based on the state of the bus voltage as opposed to the state of other nodes. A decentralized form of droop control that applies proportional control of voltage and current was implemented on four prototype nodes with each controller’s decision based on the state of the picogrid bus voltage. Individual node and overall system tests were performed on the prototype. Node tests include; open circuit, short circuit, current limit, over voltage, under voltage and effects of suddenly removing a heavy load. Sharp voltage spikes were observed when a load is suddenly disconnected from the grid due to the sudden drop of load current. These spikes were minimized by having controllers tripping the nodes immediately when the bus voltage rises. Apart from recommending future hardware improvements to the power supply circuit, A different control platform that processes faster than the one used for the picogrid was recommended in order to completely eliminate the spikes. The ease of power scaling as well as recovering from faults without requiring any user interaction was illustrated through system tests when all nodes were connected together. This further proves the picogrid to be a feasible technical solution that can be extended to a full commercial application. Furthermore, the tests show that by having more sources or storage nodes, more power can be automatically obtained from the system. The maximum power produced by a picogrid system is however limited to the hardware composition especially with regards to the node-node connector cables. Thus the cable size used will determine the maximum power of the system for deployment purposes when costs need to be taken into consideration.Item Aspects of autonomous demand response through frequency based control of domestic water heaters(2018) Cooper, Douglas JohnThis dissertation presents the design and testing of controllers intended to provide au- tonomous demand response, through the use of water heater loads and grid frequency measurements. The controllers use measured frequency as an indication of the strain on a utility grid, which allows demand side management to be isolated from any form of central control. Water heaters can operate as exible loads because their power consump- tion can be dispatched or deferred without directly impacting users. These properties make it possible to control individual water heaters based on the functioning of the grid, rather than end user input. The purpose of this research is to ultimately provide a low- cost alternative to a traditional Smart Grid, that will improve the resilience of a grid without negatively impacting users. The controllers presented here focus on ensuring that users receive hot water, while attempting to reduce any imbalance between power generated and power consumed on the grid. Simulations of these controllers in various situations highlight that while the controllers developed respond suitably to variations in the grid frequency and adequately ensure end users receive hot water, the practical bene t of the controllers depends largely on the intrinsic characteristics of the grid.Item Investigation into a high reliability micro-grid for a nuclear facility emergency power supply(2017) Lekhema, Gerard RatokaThe objective of this research work is to investigate the use of a high reliability micro grid to supply emergency electrical power to a nuclear facility following loss of offsite power (LOOP) accident. Most of the nuclear facilities around the world utilize diesel generators and battery banks as emergency power to back up the grid power supply. This power supply configuration represents the concept of the micro-grid system. The research work proposes reliability improvement of the emergency power supply by introducing diverse energy sources and energy storage systems. The energy sources and storage systems that were investigated include renewable energy sources, decay heat recovery system and large scale energy storage systems. The investigation results presented include information on the suitable energy sources and energy storage system, establishment of the reliable architectural layout and evaluation of the micro-grid system in terms of capacity adequacy and reliability.Item Analysis of the dynamic power requirements for controllable energy storage on photovoltaic microgrid(2016) Horonga, NyashaStandalone microgrid studies are being done because an expansion of the existing utility grids to supply power to remote communities is not feasible. Standalone microgrids can be considered as one of the solutions for remote communities because power can be generated close to these communities and it minimizes cost related to power transmission. Renewable energy sources with large uctuations are frequently the source of power for these standalone microgrids. The uctuating nature of these renewable sources can often lead to frequent blackouts. This research is aimed at minimizing power uctuations using controllable energy storage systems. This MSc focuses on the analysis of the ramp rate and delay time requirements for controllable energy storage system used in standalone PV microgrids. Measured insolation data and recorded load demand data for typical domestic appliances are used in this study to analyze ramp rates present. The ramp rates are then used to determine the range of energy storage ramp rate and delay time required to maintain the microgrid voltage within the standardized range of 1pu 5%. From the recorded data it has been observed that PV power can be sampled from at least 1-second intervals without losing important information. The 1 second averaged ramp rates obtained from the insolation data measurements have been found to have the highest value of 0.12pu/sec. However, this ramp rate increases to 0.3pu/sec when the allowable microgrid voltage band is narrow (1pu 5%). These insolation ramp rates are very low compared to the ramp rates of typical loads that can be connected to a microgrid. This means that, if the energy storage system is speci ed to meet the load ramp rate requirements, it will be able to respond to the uctuating PV power. The results obtained from the simulations con rm that energy storage system ramp rate plays an important role in the stability of a standalone microgrid. The minimum allowable energy storage ramp rate was found to be 8.15pu/sec for load transients with a ramp time of 20ms. This value is 28 times the energy storage ramp rate required to cancel out insolation uctuations. This further con rms that energy storage system ramp rates must be speci ed using the load demand data. The maximum allowable delay time was also found to be 0.53s to maintain the microgrid voltage within the standardized range of 1pu 5%. This delay time is applicable when canceling out only the insolation uctuations. To cancel out load transient power uctuations, there should be no delay time.Item Investigation into the steady-state load sharing of weak sources in a low voltage three-phase islanded microgrid(2016) Wu, Meng-Chun MereldaThis research investigates the power sharing between distributed energy resources with voltage and frequency droop control. A case study based on voltage sources in an islanded microgrid is set up in the laboratory, referred to as: The Example Microgrid. The Example Microgrid consists of two synchronous generators, active and reactive power loads. A simulation model is constructed based on the laboratory set-up, where componentwise and system-wise testing are completed. The simulation results are validated with the experimental set-up, and it is concluded that the model accurately represents the physical system under steady-state conditions. Further simulation studies on conventional droop controllers are conducted based on the Example Microgrid model. The results indicate that the use of conventional droop control is inappropriate for small, low-voltage islanded microgrids. As a possible application of this work, three variations of adapted droop controllers are simulated and their performance evaluated. It is found that with the adapted droop controllers, the power sharing error can be minimised