Effects of energy storage systems grid code requirements on interface protection performances in low voltage networks

The ever-growing penetration of local generation in distribution networks and the large diffusion of energy storage systems (ESSs) foreseen in the near future are bound to affect the effectiveness of interface protection systems (IPSs), with negative impact on the safety of medium voltage (MV) and low voltage (LV) systems. With the scope of preserving the main network stability, international and national grid connection codes have been updated recently. Consequently, distributed generators (DGs) and storage units are increasingly called to provide stabilizing functions according to local voltage and frequency. This can be achieved by suitably controlling the electronic power converters interfacing small-scale generators and storage units to the network. The paper focuses on the regulating functions required to storage units by grid codes currently in force in the European area. Indeed, even if such regulating actions would enable local units in participating to network stability under normal steady-state operating conditions, it is shown through dynamic simulations that they may increase the risk of unintentional islanding occurrence. This means that dangerous operating conditions may arise in LV networks in case dispersed generators and storage systems are present, even if all the end-users are compliant with currently applied connection standards

Investigation into maximizing component availability for superconducting cables in turbo-electric distributed propulsion aircraft

The commercial aviation industry is growing at a substantial rate, with demand doubling every 15 years and this trend is set to continue well into the 21st Century. At the same time regulatory pressures are being exerted on the industry as governments around the world seek to reduce their greenhouse gas emissions in an effort to contain global temperature rise to 2°C . Combined with existing infrastructure challenges, these issues are forcing air-framers to develop new, novel designs that support sustainable approaches to future aviation to meet environmental, social and economic demands. The pathway to decarbonisation of aviation will involve a combination of fuel, technology and operational measures. Many of the proposed technologies, such as electrical propulsion, are inherently disruptive and require changes to supply-chains,ground operations, maintenance standards and procedures, and pilot training. Such disruption is unavoidable given the scale of the challenge of electrical propulsion: a typical widebody jet engine for passenger aircraft can output over 22 MW fully loaded; an equivalent electrical system must be able to generate, distribute, and produce same amount of thrust with equal or greater reliability than the existing drivetrain that has been perfected over the course of the last century. Turbo-electric Distributed Propulsion (TeDP) is an approach for the electrification of propulsion systems on aircraft that aims to do this. Instead of large turbofan engines used to generate thrust, power in the engines is converted to electricity using electrical generators, and then distributed electrically through a network to propulsion motors placed in aerodynamically advantageous locations, significant fuel savings and performance benefits may be realised. Electrification of the propulsion system comes with large weight penalties. It is critical that the weight of the electrical power system does not mitigate the benefits of electrification. Superconducting electrical machines have been proposed as a route to lightweighting the electrical power system due to their promising high power densities compared to conventional electrical machines. It is proposed that the rest of the electrical power system be superconducting as far as technically possible to minimise heat sinks within the system. Integration of superconducting materials into the most safety critical aspects of commercial aviation raises multiple research questions regarding the design of resilient systems and how appropriate electrical protection strategies can be designed given the strict electric, magnetic, and thermal operating requirements that these components have. All electrical systems experience faults. This Thesis investigates how these faults manifest within a compact, power-electronically interfaced, superconducting network. The research presented in this thesis captures electrical protection requirements through modelling, simulation, and experimentation to develop requirements for TeDP feeder cables. By building on these requirements this thesis will then show how cable design can be optimised to withstand faults and present a control method which enables maximising throughput of cables during temperature rise events. This knowledge aims to improve availability, in terms of reducing the amount of superconducting network de-rating required, and power provision of superconducting feeder cables during adverse conditions encountered by superconducting TeDP aircraft.The commercial aviation industry is growing at a substantial rate, with demand doubling every 15 years and this trend is set to continue well into the 21st Century. At the same time regulatory pressures are being exerted on the industry as governments around the world seek to reduce their greenhouse gas emissions in an effort to contain global temperature rise to 2°C . Combined with existing infrastructure challenges, these issues are forcing air-framers to develop new, novel designs that support sustainable approaches to future aviation to meet environmental, social and economic demands. The pathway to decarbonisation of aviation will involve a combination of fuel, technology and operational measures. Many of the proposed technologies, such as electrical propulsion, are inherently disruptive and require changes to supply-chains,ground operations, maintenance standards and procedures, and pilot training. Such disruption is unavoidable given the scale of the challenge of electrical propulsion: a typical widebody jet engine for passenger aircraft can output over 22 MW fully loaded; an equivalent electrical system must be able to generate, distribute, and produce same amount of thrust with equal or greater reliability than the existing drivetrain that has been perfected over the course of the last century. Turbo-electric Distributed Propulsion (TeDP) is an approach for the electrification of propulsion systems on aircraft that aims to do this. Instead of large turbofan engines used to generate thrust, power in the engines is converted to electricity using electrical generators, and then distributed electrically through a network to propulsion motors placed in aerodynamically advantageous locations, significant fuel savings and performance benefits may be realised. Electrification of the propulsion system comes with large weight penalties. It is critical that the weight of the electrical power system does not mitigate the benefits of electrification. Superconducting electrical machines have been proposed as a route to lightweighting the electrical power system due to their promising high power densities compared to conventional electrical machines. It is proposed that the rest of the electrical power system be superconducting as far as technically possible to minimise heat sinks within the system. Integration of superconducting materials into the most safety critical aspects of commercial aviation raises multiple research questions regarding the design of resilient systems and how appropriate electrical protection strategies can be designed given the strict electric, magnetic, and thermal operating requirements that these components have. All electrical systems experience faults. This Thesis investigates how these faults manifest within a compact, power-electronically interfaced, superconducting network. The research presented in this thesis captures electrical protection requirements through modelling, simulation, and experimentation to develop requirements for TeDP feeder cables. By building on these requirements this thesis will then show how cable design can be optimised to withstand faults and present a control method which enables maximising throughput of cables during temperature rise events. This knowledge aims to improve availability, in terms of reducing the amount of superconducting network de-rating required, and power provision of superconducting feeder cables during adverse conditions encountered by superconducting TeDP aircraft

Evolution of microgrids with converter-interfaced generations: Challenges and opportunities

© 2019 Elsevier Ltd Although microgrids facilitate the increased penetration of distributed generations (DGs) and improve the security of power supplies, they have some issues that need to be better understood and addressed before realising the full potential of microgrids. This paper presents a comprehensive list of challenges and opportunities supported by a literature review on the evolution of converter-based microgrids. The discussion in this paper presented with a view to establishing microgrids as distinct from the existing distribution systems. This is accomplished by, firstly, describing the challenges and benefits of using DG units in a distribution network and then those of microgrid ones. Also, the definitions, classifications and characteristics of microgrids are summarised to provide a sound basis for novice researchers to undertake ongoing research on microgrids

High Penetration of Power Electronic Interfaced Power Sources and the Potential Contribution of Grid Forming Converters

The traditional electrical power system and electricity markets have been designed to work with SGs, and so these have traditionally provided various 'inherent' capabilities to the system critical to ensure the stable operation of the power systems during severe faults and even basic system survival during rare system splits. Due to the potential total absence of SGs approaches during periods of high penetration (HP) of PEIPS infeed, the wider industry has engaged in a closer examination of the lack of these system capabilities [4], [17], [31], [32]. Traditionally, the focus in the context of PEIPS has been on steady state and a limited number of dynamic (faster) aspects recently expanded to include PEIPS contributing fast fault current during system faults and extended contribution to frequency management (although this latter capability has been required from RES for more than 10 years in some countries). Demand side contributions in these contexts are emerging and have significant potential

Grid-Forming Inverter-based Wind Turbine Generators: Comprehensive Review, Comparative Analysis, and Recommendations

High penetration of wind power with conventional grid following controls for inverter-based wind turbine generators (WTGs) weakens the power grid, challenging the power system stability. Grid-forming (GFM) controls are emerging technologies that can address such stability issues. Numerous methodologies of GFM inverters have been developed in the literature; however, their applications for WTGs have not been thoroughly explored. As WTGs need to incorporate multiple control functions to operate reliably in different operational regions, the GFM control should be appropriately developed for the WTGs. This paper presents a review of GFM controls for WTGs, which covers the latest developments in GFM controls and includes multi-loop and single-loop GFM, virtual synchronous machine-based GFM, and virtual inertia control-based GFM. A comparison study for these GFM-based WTGs regarding normal and abnormal operating conditions together with black-start capability is then performed. The control parameters of these GFM types are properly designed and optimized to enable a fair comparison. In addition, the challenges of applying these GFM controls to wind turbines are discussed, which include the impact of DC-link voltage control strategy and the current saturation algorithm on the GFM control performance, black-start capability, and autonomous operation capability. Finally, recommendations and future developments of GFM-based wind turbines to increase the power system reliability are presented

Issues and Challenges of Grid-Following Converters Interfacing Renewable Energy Sources in Low Inertia Systems : A Review

The integration of renewable energy sources (RESs) is a key objective for energy sector decision-makers worldwide, aiming to establish renewable-rich future power grids. However, transitioning from conventional systems based on synchronous generators (SGs) or systems with a low RESs share presents challenges, particularly when accompanied by decommissioning large central generation units. This is because the reduction in inertia and system strength, traditionally provided by SGs, can lead to a loss of essential system support functions like voltage and frequency. While current converter technologies attempt to compensate for the grid support provided by SGs by enhancing converter capabilities, they still heavily rely on the presence of SGs to function effectively. These converters, known as grid-following (GFL) converters, depend on the grid to operate in a stable and secure manner. As the penetration of RESs increases, the efficacy of GFL converters diminishes, posing stability challenges in low inertia systems and limiting the integration of RESs. Therefore, it is crucial to reassess the existing GFL converter technologies, control mechanisms, and grid codes to understand their status and future requirements. This will shed light on the advancements and limitations of GFL converters, enabling greater RESs integration and grid support independent of SGs. This paper aims to provide an up-to-date reference for researchers and system operators, addressing the issues and challenges related to GFL converter technologies, control systems, and applications in low inertia systems. It serves as a valuable resource for facilitating the transition towards future systems with 100% RESs penetration scenarios.© 2024 The Authors. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/fi=vertaisarvioitu|en=peerReviewed