3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Realisation of AD hoc renewable rural power systems with decentralised active power dispatch techniques(2019) Lange, Jarren HiltonAd hoc power systems offer a promising opportunity to provide affordable reliable renewable energy to rural areas. Classical grid solutions are impeded by low population densities and poor economic conditions that perpetuate energy poverty in large areas of rural Africa. Existing islanded renewable energy based solutions can not typically be expanded at will as the needs of its users increase. Scalable power systems, that can lower the engineering costs of commissioning and modifying the system represents a potential solution to energy poverty. Existing solutions rely on the ability to tightly model and control all elements a result of the stringent requirements imposed on these systems. Meaning scalable power systems are theoretically unrealisable. Thus, this is a system architecture and control issue, not a generation or storage issue. This thesis explores ways to realise low cost scalable power systems for low (> 1 kW) to medium (< 1 MW) power requirements. Allowing power system parameters to indefinitely deviate from nominal values, which discards a 140 year old assumption, is achievable in new electronic generation based power systems. This allows all system elements to contribute towards system operation without additional communication. Modelling is presented which simplifies complex power interactions in AC systems to passive circuit components. The desired characteristics of each element while utilising existing technologies can be identified from this modelling. These techniques, which are demonstrated and verified on a hardware based power system simulator, enable scalable economically feasible renewable power systems. This provides a novel, flexible and robust alternative to existing power systems that enables the affordable decentralised ownership and operation of renewable power systems at a household level.Item Investigation into the impact of wind generation on the inter-area and local oscillation modes of power systems(2018) Chidzikwe, CliffThe operation and dynamic characteristics of power system grids with mixed generation technologies in particular synchronous generators and wind turbine generators are receiving great attention towards the better understanding of the modern power system stability. Wind power generation introduces new types of non-conventional generators that are being operated in parallel with conventional generation. However, as the penetration of wind energy increases, the power system dynamics and behaviour are modified. It is thus important to understand and quantify the impact of wind energy technologies on the performance of the interconnected power systems. The investigation in this dissertation focuses on the impact of wind power generation on the power system small-signal stability. The focus is on the variable speed Type 4 Wind Turbine Generators (WTGs) and the Wind Power Plants (WPPs) impact on the inter-area and local oscillation modes of the power systems. An aggregated WPP model based on the generic IEC 61400-27-1 (2015) Type 4 WTG of varying capacities was used in this investigation together with a multi-machine small-scale power system comprising conventional synchronous generators and their associated controls. The Power System Stabilizer (PSS), an additional generator control, is widely used to resolve the power system small-signal stability problems by providing additional damping to the inter-area and local oscillation modes. This investigation considered the impact of wind power on the inter-area and local oscillation modes without and with PSSs installed on the synchronous generators. The procedure involved employing small-signal stability analysis through eigenvalue analysis and tracking the oscillation modes after the integration of wind power generation sources. The investigation has shown that the introduction of wind power in parallel with synchronous generators alter the generator operating conditions and the power flows causing the inter-area and local oscillation mode characteristics to change. As the wind power penetration increases, the inter-area and local mode frequencies decrease. The decrease in frequencies has been attributed to the change in the operating conditions of synchronous generators when operated in parallel with wind turbine generators. It was further found that wind power can have negative or positive impact on the damping of inter-area and local modes. However, for the particular case studies examined, this investigation suggests that PSSs already installed in the absences of wind power generation sources do not require retuning. The work recommends that power system small-signal stability requirements in the presence of wind power should be investigated as this is a unique characteristic for a given network.Item Local contect requirements and the manufacture of solar photovoltaic components in South Africa(2018) Kuzwayo, MandlesizweThe outputs in this report are based on the experiences, beliefs and perceptions of a crosssection of Solar Photovoltaic industry stakeholders on whether Local Content Requirements is an appropriate policy instrument for building a local industry and the extent to which the Local Content Requirements of the Renewable Energy Independent Power Producer Procurement Programme have led to an increase in the South African solar component manufacturing capacity since the programme’s inception in November 2011. Protectionist policies, including Local Content Requirements, were used by now industrialised countries to develop their respective countries, and continue to be used to this day despite World Trade Organisation prohibitions. Four models on building local industries are discussed and their relationship to the two research questions explored. Interview participants agreed that the Renewable Energy Independent Power Producer Procurement Programme was instrumental in building a large-scale local renewable energy industry in the country, created jobs and excitement around manufacturing capacity potential. However, many believe that programme design and implementation interventions are required to improve the programme’s localisation impacts. The latest draft Integrated Resource Plan’s sizeable allocation for Solar Photovoltaic until 2030 presents an opportunity to drastically improve localisation benefits for the country.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.