Voltage rise mitigation at the point of common coupling of large renewable distributed generation and distribution network

Abstract

A lot of changes are taking place in the power system as a result of the introduction of Renewable Distributed Generation (RDG) (e.g., wind and PV systems). Gradually, electricity generated by fossil fuel is being replaced by electricity generated from Renewable Energy Sources (RESs). The deregulation of generation, transmission, and distribution systems due to the introduction of RDGs has brought competition to the electricity market. The electricity generation assets are no longer owned by one or a few owners, as investors have been attracted to the electricity market. Individuals can now generate their own electricity from renewable energy sources such as solar, wind, hydro, wave, tide, and geothermal etc. RDGs are predicted to play a crucial role in the power system transformation in the near future; they are the key to a sustainable energy supply infrastructure because of their inexhaustible and non-polluting nature. However, the integration of RDGs into the power system would have an impact on power system planning, voltage profiles and power quality requirements within the Distribution Network (DN). The voltage rise (or over-voltages) at the busbars within the conventional power system with centralized large power generating units are actually of less concern due to advances in control and protection technologies, but the issue of excessive voltage drop at the far end of transmission lines cannot be overemphasized. The introduction of RDGs into the power system has eliminated the occurrences of the severe under voltage at the far end of transmission lines, but the voltage rise effects and the bidirectional power flow issues at the point of common couplings (PCCs) between RDGs and DN are now of major concern. Indeed, the integration of RDGs can make the power system become bidirectional as electricity can flow from RDGs as well as from DN with a centralised generator. This causes various problems with regards to the power quality, power flow control, frequency control, system voltage profile, etc. Furthermore, the voltage rise effects at PCC with connected-RDG has been a noticeable issue in recent years and requires remedial action. The standard grid code requires that output parameters of RDGs (i.e., voltage profile, current, voltage-current harmonic distortions, power factor, frequency, etc.) at PCC shall be regulated to avoid damage to sensitive equipment connected to the DN, meet up with the power quality criteria, and shall continue providing power support to the DN. Hence, this study focuses on the following two main problems: – firstly, the voltage rise effect, and secondly, the bidirectional power flow constraint at the PCC between RDGs and DN. The analysis and simulations in this thesis are conducted on an IEEE 13-bus sample model and DUT Steve Biko network with penetration of a large RDG. The capacity of the RDG integrated to DN is 1 MW (solar PV). In order to investigate the effect of voltage rise and bidirectional power flow in a DN, a mathematical model of a power distribution network connected with RDG is developed. Intensive simulations are carried out using MATLAB/Simulink software. Furthermore, a control strategy is recommended at PCC for mitigating or minimizing the impacts of voltage rise and reverse power flow when operating at a worst critical scenario, such as minimum load and maximum generation. The control structure consists of the installation of a static compensator (STATCOM) with Pulse Width Modulation (PWM), and the block/deblock and in-loop filtering circuit control scheme to control the active and reactive power. The proposed control strategy also mitigates the voltage-current harmonic distortions, improves the power factor and voltage stability at PCC, and also protects the converter-PWM scheme from grid disturbances and fault currents, as the control of active and reactive power is independent of the grid. This thesis also provides a review of various types of renewable energy resources (RERs) prospects in Africa, looking at how they can be deployed faster within the continent. The thesis also analyses power quality and compensators.