Novel metrics to quantify the impacts of frequency support provision methods by wind power

This paper introduces two novel metrics to judge the capability and influence of wind power to provide virtual inertia response (i.e. frequency support). The first metric considers the generation unit (i.e. wind turbine generator (WTG)/wind farm (WF) vs. synchronous generator). This metric is applied to compare between three different methods of provision of frequency support. The second metric assess the improvement or hindering in frequency response at the point of common coupling (PCC) between a WF and a synchronous area. This metric is critical especially to WFs that are connected via High Voltage Direct Current (HVDC) or Low-frequency AC links. Both metrics are universal so that they could be applied to any support method, and any power system. The first metric is applied to assess the virtual inertia response of an offshore WF, which is considered as a power plant along with the HVDC transmission link. Results assure the positive impact of the provision of frequency support by wind power. This impact is quantified could be used to tune frequency support controllers, and optimize system planning. It is verified that no obstacles are implied by the HVDC link to integrating frequency support methods, as the WF dominates the support proces

Compilation of Development Metrics Applicable to Wave Energy Converters (WECs): Current Status and Proposed Next Steps

As for any novel technology, the need to consider, identify and formulate performance requirements and related assessment criteria has been an important subject in the development of Wave Energy Converters (WECs). These allow the characterisation of each technology through techno-economic indicators, which in turn allow comparisons between different technologies, and an assessment of alternative solutions throughout all the development stages. Such assessment is ideally carried out through the application of metrics, which should comply with several attributes, such as being objective, quantitative, specific, measurable, repeatable, and independent. In the present work, more than 50 metrics to monitor the development of WECs are compiled, explained, and discussed. These metrics are divided in the following evaluation areas: 1) Performance; 2) Reliability; 3) Survivability; 4) Techno-economics. In addition, the important evaluation area of Environmental Impact is briefly discussed concerning the need for common metrics. The compilation summarised in this paper and its discussion aim to provide a practical reference source concerning metrics for WEC development, which is currently unavailable in the published literature in terms of broadness and condensed presentation. Such compilation includes multiple formulations from the wave energy sector and other relatable industries (e.g. wind energy) that are typically diluted among specialist literature, standards, guidelines and recommendations, scientific papers, and project reports. The paper is concluded with a reflection of any salient gaps that are not addressed by current metrics, in a context of accelerating the development of WEC technologies

Towards optimal operation of power systems with high IBR penetration: a stability-constrained optimization approach

Renewable Energy Sources (RES) have been massively integrated into the modern electric power system in the past few decades due to the environmental and sustainability concerns throughout the world. As a result, the power electronic converters are anticipated to acquire a steadily increasing role as they are the key element for the interface between RES and the grid. However, owing to the intermittency of the RES and the distinguished features of the Inverter-Based Resources (IBRs). The main focus of this thesis is to develop optimal system operation strategies to maintain the security and stability of the grid while considering the fast and accurate control of the IBR units. To achieve this, we investigate challenges in different areas. Regarding system frequency and low inertia issues, the main challenges are the incorporation of differential equation-based frequency dynamics into algebraic equation-based optimization problem as well as the optimal utilization of the frequency support from different sources. We first target on the optimal system scheduling on a transmission system level to achieve system operation cost minimization while maintaining the frequency security. In addition, the frequency stability problem in microgrids after unintentional islanding events is also studied. We consider the frequency support from WTs, PV and storage systems as well as noncritical load shedding to ensure the microgrid frequency security after unintentional islanding events. Furthermore, a SCC-constrained Unit Commitment (UC) model is developed, maintaining a minimum SCC level at different locations in the system such that enough reactive current could be supplied during the fault to trigger the protection devices and maintain the post-fault voltages. Moreover, the static voltage stability in systems with high IBR penetration is also investigated considering the interactions among the IBR units and their reactive power support capability within rating limits.Open Acces

Methodologies for Frequency Stability Assessment in Low Inertia Power Systems

L'abstract è presente nell'allegato / the abstract is in the attachmen

Quantification and mitigation of the impacts of extreme weather on power system resilience and reliability

Modelling the impact of extreme weather on power systems is a computationally expensive, challenging area of study due to the diversity of threats, complicatedness of modelling, and data and simulation requirements to perform the relevant studies. The impacts of extreme weather – specifically wind – are considered. Factors such as the distribution of outage probability on lines and the potential correlation with wind power generation during storms are investigated; so too is sensitivity of security assessments involving extreme wind to the relationships used between failures and the natural hazard being studied, specifically wind speed. A large scale simulation ensemble is developed and demonstrated to investigate what are deemed the most significant features of power system simulation during extreme weather events. The challenges associated with modelling high impact low probability (HILP) events are studied and demonstrate that the results of security assessments are significantly affected by the granularity of incident weather data being used and the corrections or interpolation being applied to the source data. A generalizable simulation framework is formulated and deployed to investigate the significance of the relationship between incident natural hazards, in this case wind, and its corresponding impact on system resilience. Based on this, a large-scale simulation model is developed and demonstrated to take consideration of a wide variety of factors which can affect power systems during extreme weather events including, but not limited to, under frequency load shedding, line overloads, and high wind speed shutdown and its impact on wind generation. A methodology for quantifying and visualising distributed overhead line failure risk is also demonstrated in tandem with straightforward methods for making wind power projections over transmission systems for security studies. The potential correlation between overhead line risk and wind power generation risk is illustrated visually on representations of GB power networks based on real world data.Open Acces

A methodological approach for assessing flexibility and capacity value in renewable-dominated power systems: A Spanish case study in 2030

Maintaining the security of supply is one of the challenges that system operators face. Variability and uncertainty increase due to the penetration of variable renewable energy sources such as solar and wind, while flexible technologies such as traditional thermal units are phased out to reduce emissions. The current methods for assessing power system adequacy are based on historical operations and are generally intended to be applied to thermal-dominated electricity systems. Therefore, it is necessary to improve current adequacy assessment methods since they usually neglect the flexibility of power systems. This paper presents a methodological approach for jointly assessing the adequacy and flexibility of power systems. The methodology's usefulness is demonstrated through its application to the Spanish power system. For the case study, results show that new closed-looped pumped storage hydro technology provides 25% flexibility while contributing to adequacy due to higher installed capacity and round-trip efficiency. Due to shorter storage duration, batteries only contribute to flexibility, supplying 16% of the total operating reserves. Therefore, this study shows that metrics of flexibility and individual contribution to the power system adequacy complement each other and simultaneously enable the scarcities of power systems to be observed.This research has been carried out thanks to the Spanish Ministry of Economy and Competitiveness MINECO through BC3 María de Maeztu excellence accreditation MDM-2017-0714 Maria de Maeztu Grant