Power quality control algorithms for small scale power intergration systems

The electrical power system is a means of supplying energy that is intended to generate, transport and supply electricity to various kinds of loads that are connected to it. The electricity providers strive to supply their customers with steady and uninterrupted sinusoidal power as they function. Traditional power plants primarily rely on fossil fuels such as coal for their energy source. Because of the influence of global warming, air pollution is becoming a major concern in traditional coal-based power generation, and measures to reduce it have been implemented. South Africa is among the many African nations that have ratified these international agreements. Incorporating renewable energy sources is the sole method to establish an environmentally friendly power generation system. Integrating various energy resources at the distribution level is possible and helps to reduce transmission power losses. However, integration of renewable energy resources requires the use of advanced non-linear technological equipment which causes some technical problems. Amongst technical problems that may be faced is high penetration of solar Photovoltaic (PV) which results in voltage swell power quality issues whilst excessive connection of non-linear load results in current harmonics.

The thesis examines the use of Custom Power Devices (CPDs) such as Dynamic Voltage Restorer (DVR), Distribution Static Compensator (DSTATCOM), and Unified Power Quality Conditioner (UPQC) for voltage and current-related power quality issues. The CPDs depend on the DC link voltage from the storage element used which is not always sufficient and the compensation of the power quality issues fail. The use of small-scale solar PV for the support of the DC-link storage element used in the CPDs is explored.

A DVR has been proposed for the mitigation of voltage-related issues to ensure that the grid supplies power with voltage variation to sensitive loads. The load is protected from such and in the case where the DC link storage is not enough solar PV will support the DVR. However, this type of compensation has proved unable to deal with harmonics caused by the non-linear load connected to the system which meant another CPD has to be proposed for current related issues. A DSTATCOM is a device that can used for compensation of current-related power quality issues but also cannot deal with voltage power quality issues. A right shunt UPQC has been proposed as a combination of the two devices connected back-to-back through the DC link side for voltage and current multiple power quality issues. Optimisation of effective compensation for the CPDs depends on the proper selection of control algorithms for the gate switching of the Voltage Source Converters (VSCs) used. A control algorithm has been implemented considering the stated dynamic behaviours of the power system to ensure that the CPDs can restore the power quality required by the consumer and the utilities as regulated by IEEE standards. The modelling and simulation were performed on MATLAB Simulink simulation software.