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Faculty of Engineering and Built Environment

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Author: search.filters.author.Hamatwi, E.

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    Control of multi-level voltage source converters integrating a wind turbine system into the grid
    (IEEE, 2016) Hamatwi, E.; Davidson, Innocent E.; Gitau, M.N.
    In recent years, wind energy has proven to be the most competitive and environmental friendliest renewable energy (RE) source for generating electricity. Wind farms are more likely to be located far from the load centres, and hence the generated power has to be transmitted over long distances. A high voltage direct current (HVDC) transmission system increases the transmission capacity, improves the system stability, and possesses lower transmission losses. Therefore, it is the preferred means for power delivery over long distances compared to the high voltage alternating current transmission system. In this paper, a 690V, 2MW wind turbine is modelled to be integrated into a 33kV AC grid via a 3-level Neutral-Point-Clamped Voltage Source Converter-based HVDC transmission system. Three control schemes were implemented: a pitch-angle controller, a controller applied to the generator-side converter, and a controller applied to the grid-side converter. The proposed wind energy conversion system and control schemes were implemented in MATLAB/SIMULINK and simulations were carried out to analyse the performance of the system.
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    Optimisation of a hybrid PV-diesel system for rural application : the case of Oluundje village, Namibia
    (University of Namibia, 2017) Hamatwi, E.; Nyirenda, C. N.; Davidson, Innocent Ewaen
    The absence of electricity in remote and rural areas is one of the major challenges faced by many poor and developing countries. Hybrid energy systems (HES) based on photovoltaics (PV) are considered to be an effective option to electrify remote and isolated areas, which are far from conventional grids. This is true for areas that receive high averages of solar radiation annually. This research investigation involves the modelling, simulation and optimization of a PV-Diesel hybrid system for Oluundje village in Namibia. A site survey was conducted in a form of questionnaires and interviews for the purpose of load forecasting and system modelling. HOMER software was used to design and model the proposed hybrid energy system. Costs of different components, hourly solar radiation, and rating parameters are inputs of the simulation program. Sensitivity analysis was carried out using Homer. The optimal PV-Diesel hybrid system and diesel-generator-only system were compared both technically and economically. Based on simulation results, it was found that electrifying a remote village using a PVdiesel hybrid system is more advantageous when compared to the diesel-generator-only system as it has lower operating costs and emissions. This system may be used as a preliminary design to guide in the planning and modelling of similar systems for other remote villages.
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    Modeling and control of voltage source converters for grid integration of a wind turbine system
    (IEEE, 2016) Hamatwi, E.; Davidson, Innocent E.; Gitau, M. N.; Adam, G. P.
    Wind energy is one of the most promising renewable energy sources for generating electricity due to its cost competitiveness when compared to the conventional energy sources (fossil fuels). Wind farms are usually located far from the loads for minimal disturbances and optimal power generation. High Voltage Direct Current (HVDC) transmission is the preferred bulk power transmission system over long distances due to the minimal transmission losses, low costs and reduced environmental impacts. In this research investigation, a 690V, 2MW wind turbine equipped with a PMSG is modelled to be integrated into a local 33kV AC grid via a 2-level VSC-based HVDC transmission system. Three control schemes are implemented on the proposed system: a blade-pitch-angle controller applied on the wind turbine model, a field-oriented rotor speed controller applied on the rectifier for maximum power extraction, and a vector-oriented direct-current-link voltage controller applied on the grid-side inverter to keep the DC-link voltage constant and to ensure unity power factor. The proposed subsystems are implemented in MATLAB/Simulink and simulations are carried out to analyze the overall system’s performance.