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Faculty of Engineering and Built Environment

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    Evaluation of grid-scale battery energy storage system as an enabler for large-scale renewable energy integration
    (2022-09-29) Loji, Nomhle; Davidson, Innocent Ewaen; Akindeji, Timothy Kayode
    Because of many substantial benefits over other renewable energy resources (RES), photovoltaic (PV) and wind technologies are the most important emerging renewable energy sources (RES) and they are rapidly and widely propagating. However, they are nondispatchable and, the stochastic and intermittent natures of solar irradiation and wind, are some of the fundamental barriers and challenges to their development and their large-scale deployment. As a result, power systems operators have no control over DG’s available resources and are compelled to operate conventional generators to both cater for normal changes in load demand and make provision for DG’s output variations. These concerns lead to increase the uncertainty in power systems operation as they modify both the structure and the operation of the distribution network by affecting inter alia, the voltage profile and stability, the direction of network power flow and the overall performance of the power system. Enabling PV penetration into electrical grids require a balance of supply and demand that cannot be achieved by oneself. Because of the flexibility to control their real power output, batteries are suggested as a suitable and cost effective solution to mitigate the adverse effects of intermittency and shape the fluctuation of the system’s output into relatively constant power. There is a need to quantitatively investigate and evaluate the performance of the use of BESS that adequately smoothen the output of the PV-BESS sub-system for over-voltage reduction and peak load shaving during the high PV generation – low consumption time in lieu of power curtailment or reactive power injection. Using DigSILENT™ - PowerFactory™ this research work investigated the impacts of BESS on voltage stability and power losses with the aim of increasing system loadability and enhancing stability. A modified standard IEEE 9-Bus was used to perform the studies using four cases and various scenarios and the simulation results and comparative analysis first reveal that the combined effect of the Solar PV-BESS system has a substantial positive impact on the system loadability improvement and reduction of the total power system losses. Results further confirmed the BESS’s ability to act as generator, or load, respectively during high load demand/lower PV generation and lower demand//higher Solar PV generation to contribute to the voltage regulation and power system stability, offsetting effectively the intermittency of Solar PV energy sources and subsequently enabling greater RE penetration.
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    Voltage rise mitigation at the point of common coupling of large renewable distributed generation and distribution network
    (2022-02-24) Akinyemi, Ayodeji Stephen; Kabeya, Musasa; Davidson, Innocent Ewaen
    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.
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    High voltage transmission system planning for a southern African regional grid
    (2022-09-29) Ndlela, Nomihla Wandile; Davidson, Innocent Ewaen
    It is proposed to use highly complex power system controllers to integrate African power grids into super-grids capable of accepting high levels of renewable energy penetration while maintaining power quality, active and reactive power flow, voltage, and power system stability. The proposed super-grid is built with ultra-high voltage direct current (UHVDC) and flexible AC transmission systems (FACTS), as well as dedicated AC and DC interconnectors with intelligent system applications, to create a Smart Integrated African Super-Grid. DC interconnectors will divide the continent's power grid into five substantial asynchronous portions (regions). Asynchronous segments will restrict AC fault propagation across segments while permitting power interchange between various regions of the super-grid, with minimal difficulties for grid code unification or harmonization of regular design regimes across the continent, as each segment retains its autonomy. A Smart African Integrated Electrical Power System Super-Grid powered by these technologies is critical to Africa's long-term economic growth and development; it is built on the foundation of green energy and harnesses over 200GW untapped potential of Africa's clean renewable hydro-electric, solar-PV, and wind power as part of a vast energy mix comprised of conventional and alternating energy resources. The proposed Super-Grid will power Africa's emerging economy and serve its 1.3 billion people by facilitating electricity trading and power exchange between regional power pools and countries. This study focuses on the development of the Southern African Power Pool (SAPP), into a robust Southern Africa regional grid (SARG), and prospects for a Smart Integrated African Super Grid. The Southern African countries have the potential to have a reliable, sustainable, and efficient electrical power grid; thus, the use of renewable energy is strongly encouraged, as is upgrading the existing AC grid, including encouraging power interconnections to exchange power more specifically for long-distance transmission networks when transmitting bulk power using High Voltage Direct Current (HVDC) and installing suitable FACTS controllers to maximize power transfer. Thus, the modernization of the traditional Power Grid into a Smart Grid will enable two-way digital communication technology by providing utilities with real-time, precise data on electricity demand, power outages, and quality of supply. This study develops a load flow model for a robust Southern African Regional Grid, and introduces a number of power interconnections for power exchange in the Southern African Regional Grid, to increase grid reliability, and reduce electrical losses. This load flow analysis was carried out using DIgSILENT PowerFactory. Results obtained from varying the load and observing the generator and transmission lines for different scenarios, using HVDC, and HVDC transmission links with FACTS controllers, are discussed and presented. This study is valuable as we seek to enable all SAPP countries to interchange power more efficiently, especially those who lack access to electricity
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    Modelling and fault ride-through control of grid supporting inverter-based microgrid
    (2021-03-02) Buraimoh, Elutunji; Davidson, Innocent Ewaen
    This thesis is focused on modeling and fault ride-through control, local load power delivery, and grid power exchange of power electronic interfaced Distributed Energy Resources (DERs) for grid supporting microgrids. Active and reactive power regulations are the requirements for a grid-supporting system operating as a current source, while frequency and voltage magnitude regulation in the grid-supporting system acting as a voltage source. Consequently, these are put into consideration as the primary control requirements for the inverter-based microgrid. To that end, two discrete-time models of a grid-feeding system and grid-forming system were developed to serve as controls for a single DER operating in grid-connected mode and islanded mode, respectively. Consequently, for the first set of mathematical models: grid feeding and grid forming were interfaced with a droop control to allow for parallel operation of additional DERs for power coordination within the microgrid for grid-connected and islanded operation. However, virtual impedance was incorporated into the grid-supporting system's droop control operating as a voltage source to emulate the link feeder's physical impedance to the main grid. Based on the developed grid supporting models, the microgrid primary control schemes effectively delivered power to the host grid and simultaneously contributed to the grid's frequency and voltage regulation. Furthermore, to ensure grid code compliance and ensure the microgrid provides ancillary services to the host grid, such as fault ride-through and reactive power compensation for voltage recovery, a novel technique is proposed in the microgrid's secondary control. The secondary control realizes the fault ride-through for the grid supporting system using a delay signal cancellation algorithm for negative sequence detection. The proposed control scheme actualizes grid code requirements by providing a secondary voltage control, which is active and more prominent in the transient period of faults without mode switching. The strategy's performance is further enhanced with an IGBT-Diodes switched AC reactor to improve the voltage and prevent the transient overcurrent in the microgrid during the grid fault. This ensures a continued supply of the microgrid's local sensitive load while meeting the grid code requirement. Similarly, the active power injection into the main grid is limited to maximize reactive power injection into the main network to support the grid voltage sag. The detection algorithm using the delayed signal cancellation algorithm is implemented to detect the instance of fault in 1.6% of the half-cycle under grid disturbance/fault to activate the proposed secondary control. This effectiveness and fault ride-through compliance of the developed control models were tested on an inverter-based microgrid system with an ideal voltage source DERs. Finally, to accommodate for the grid dynamics introduced to the DC link parameters of an ideal voltage source DER such as PV, the models were also implemented and assimilated for a solar PV sourced DER used with a grid supporting inverter-based microgrid. The injection of active power into the main grid is constrained by systematically shifting the MPPT operating point based on voltage sag depth to maximize reactive power injection to support the grid voltage sag. The strategy developed in the PV sourced system also ensured that the DC-link voltage and AC grid current raises are suppressed while meeting microgrid load requirements. The models' implementation, DER primary control, and proposed secondary control schemes are established through detailed time-domain simulation studies using MATLAB Simscape Electrical™ and Control System™.
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    A technical and financial analysis of smart prepaid split meters on Eskom's electric power distribution
    (2021-05-27) Ndaba, Sindi Iren; Davidson, Innocent Ewaen
    The implementation of a smart metering system in the distribution network does not only promote energy loss reduction, but also improves smart grids. This improvement in smart grids is achieved by the high level information infrastructure, monitoring, accurate measurement and metering operations that provide a widespread communication substructure. The direct effect of smart prepaid split meters is on energy flow management and billing advancing, to aiding the power quality when combined with a smart grid system. The study focused on the technical and financial effectiveness of the smart prepaid split metering system on the Eskom distribution network. The objectives of the study were, to investigate the severity of non-technical losses in distribution networks before and after smart prepaid split metering roll-out; to investigate the effectiveness of smart prepaid split metering for the utility and customers; to analyze the technical performance on medium voltage (MV) and low voltage (LV) power distribution networks before and after smart prepaid split metering roll-out; and to analyze the effectiveness of smart prepaid split metering for revenue collections. The questionnaire instrumental survey and historical data were used for the analyses. The primary data was obtained from the questionnaire tool. The collected data were analyzed with the Statistical Package for the Social Sciences software (SPSS) version 26.0 and Microsoft Excel 2016 in order to achieve multiobjective decision-making on the effectiveness of smart prepaid split metering in the utility and customer satisfaction. The different inferential statistics techniques used included regressions, correlations, multifactor analysis (MFA), factor analysis (FA) and chi-square test values. These were interpreted using the p-values to identify the change-point, trend and correlated best-fit time series for decision making. This study concluded that the use of a smart prepaid split metering system faces challenges such as a shortage of experts for new smart meter technology to respond to the faults which led to unfavorable results for power system average interruption duration. The study recommended that South Africa’s power utility (Eskom) should consider educating and train more technical officials concerning smart grids and smart metering to ensure that this metering technology, which is still in the early stages of development, functions efficiently
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    Integrating the power transformer protection scheme to Telecontrol Terminal Unit (RTU)
    (2018-12) Madonsela, Bhekinkosi Pheneas; Davidson, Innocent Ewaen; Mulangu, T. C.
    Automated substations and distribution networks are key element of smart grid, however not all substations and distribution networks are automated to date due to the numerous reasons such as cost related to automation and scarcity of skilful workforce. With the drive to integrate renewable energy to the national smart grid, the advanced and innovative integrating methodologies need to be investigated. Automating the power system is the effort to improve power supply security, availability and reliability. Reliability is very important in substation automation systems and is achieved through real-time monitoring of the substation data. The interconnection of substation through substation automation devices is crucial because it provide the backup link to the network in case one substation fails. The utilities has developed a remarkable interest in substation automation due to the benefit its offers such as; reduction in maintenance and, operating cost and improved revenues due to stable power system networks. Substation automation is made up of four main functions that need to be fused together; protection, control, monitoring and, local and remote communications. There are numerous communication protocols available in the market for substation automation applications. However not all of them are utilized in the current application of smart grid.DNP3 and IEC61850 are the leading communication protocols currently. DNP3 has proved its technical advantages over the past few years in substation automation applications. On other hand IEC61850 was only published in 2003 and became more popular in substation around 2006; the standard is only fifteen years old. IEC61850 define the protocols such as; GOOSE, SMV, GSSE, GSE and MMS using its communication profiles. This research will investigate the possibilities of integrating DNP3 data point into IEC61850 data model. With this approach; the legacy substation shown in figure 1.1 will inherit the advantages of IEC61850 such as high speed data exchange, interoperability and interchangeability
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    Modeling and recognition of faults in smart distribution grid using maching intelligence technique
    (2018) Onaolapo, Adeniyi Kehinde; Akindeji, Timothy Kayode; Adetiba, Emmanuel
    Electrical power systems experience unforeseen faults attributable to diverse arbitrary reasons. Unanticipated failures occurring in power systems are to be prevented from propagating to other parts of the protective system to enhance economic efficacy of electric utilities and provide better service to energy consumers. Since most consumers are directly connected to power distribution networks, there is an increasing research efforts in distribution network fault recognition and fault-types identifications to solve the problem of outages due to faults. This study focuses on fault recognition and fault-types identification in electrical power distribution system based on the Design Science Research (DSR) approach. Diverse simulations of fault types at different locations were applied to the IEEE 13 Node Test Feeder to produce three phase currents and voltages as data set for this study. This was realized by modelling the IEEE 13-node benchmark test feeder in MATLAB-Simulink R2017a. In order to achieve intelligent fault recognition and fault-type identification, different Multi-layer Perceptron Artificial Neural Networks (MLP-ANN) models were designed and subsequently trained using the generated dataset with the Neural Network toolbox in MATLAB R2017a. The fault recognition task verifies if a fault occurs or not while the fault-types identification task determines the fault class as well as the faulty phase(s). Results obtained from the various MLP-ANN models were recorded and statistically analyzed. Acceptable performances were obtained for fault recognition with the 6-25-20-15-1 MLP-ANN architecture, for fault-types identification with the 6-40-4 MLP-ANN architecture and for fault location with the 6-30-15-5-4 MLP-ANN architecture. Given the result obtained in this study, MLP-ANN is adjudged suitable for intelligent fault recognition and fault-types identification in power distribution systems. The trained MLP-ANNs in this study could ultimately be incorporated in power distribution networks within South Africa and beyond in order to enhance energy customers’ satisfaction.