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Faculty of Engineering and Built Environment

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    Application of optimal control for power systems considering renewable energy technologies
    (2021-03) Chetty, Dhanpal; Sharma, Gulshan; Davidson, Innocent Ewaen
    Over the last decade, power generation from renewable energy sources such as wind, hydro and solar energies have substantially increased globally and in South Africa. Of all the renewable energy sources, wind energy appears to be the most promising, considering design and costs. However, due to the intermittent nature of wind, the increased integration of wind energy into existing power systems raises several control challenges related to load frequency control (LFC) and tie-line power system stability. The stability of modern power systems, incorporating wind energy generations, will be significantly enhanced with the development of LFC strategies based on modern control theory, which is the focus of this research. This thesis presents the design, modelling and analysis, of two LFC control strategies for interconnected power systems, having wind power integrations. The first design is an optimal control strategy, based on error minimization through full state vector feedback, for a two-area interconnected power system consisting of hydro-thermal generations. The second design is a model predictive control (MPC) strategy, based output vector feedback of system state parameters, for a two-area interconnected power system consisting of thermal generations in each area. Both designs include the active power support from doubly fed induction generator based wind turbines (DFIG) in conjunction with the combined effort of a thyristor control phase shifter (TCPS) and super conducting magnetic energy storage unit (SMES). Both control strategies were simulated in MATLAB Simulink and positive results were obtained. The results show that the optimal control strategy is enhanced with power integrations using DFIG based wind turbines combined with the TCPS-SMES units and the MPC strategy is very robust and provides better dynamic performances even with parameter variations and generation rate restrictions.
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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.