Mitigating the erosion of transient stability margins in Great Britain through novel wind farm control techniques

The predominant North-to-South active power flow across the border between Scotland and England has historically been limited by system stability considerations. As the penetration of variable-speed wind power plants in Great Britain grows (reducing the generation share of traditional synchronous generation), it is imperative that stability limits, operational flexibility, efficiency and system security are not unduly eroded as a result. The studies reported in this thesis illustrate the impacts on critical fault clearing times and active power transfer limits through this North-South corridor, known as the B6 boundary, in the presence of increasing penetrations of wind power generation on the GB transmission system. By focussing on the transient behaviour of a representative reduced test system following a three-phase short-circuit fault occurring on one of the two double-circuits constituting the B6 boundary, the impacts on the transient stability margins are qualitatively identified. There is a pressing necessity for new wind farms to be able to mitigate, as much as possible, their own negative impacts on system stability margins. The transient stability improvement achieved by tailoring the low voltage ride-through reactive power control response of wind farms is first investigated, and a novel control technique is then presented which can significantly mitigate the erosion of the transient stability performance of power systems, in the presence of in-creasing amounts of wind power, by tailoring the immediate post-fault active power recovery ramp-rates of the wind power plants around the system. The impacts of these control techniques on critical fault clearing times and power transfer limits are investigated. In particular, it has been found that the use of slower active power recovery from wind farms located in exporting regions when a short circuit fault occurs on the export corridor will provide significant benefits for both of these metrics, while a faster active power recovery in importing regions will provide a similar transient stability benefit. However, it is also shown that there are potential detrimental effects for system frequency stability. In addition, important impacts of wind farm settings in respect of low voltage ride through are revealed whereby the LVRT controls can act to erode stability margins if careful consideration of their settings is not taken. Assuming a future power system with high levels of centralised observability and controllability (or decentralised co-operative control systems), it may be possible to continually “dispatch” the reactive power gains and active power recovery ramp rates discussed in this thesis to match the current system setpoint and to seek an optimal transient response to a range of credible contingencies.The predominant North-to-South active power flow across the border between Scotland and England has historically been limited by system stability considerations. As the penetration of variable-speed wind power plants in Great Britain grows (reducing the generation share of traditional synchronous generation), it is imperative that stability limits, operational flexibility, efficiency and system security are not unduly eroded as a result. The studies reported in this thesis illustrate the impacts on critical fault clearing times and active power transfer limits through this North-South corridor, known as the B6 boundary, in the presence of increasing penetrations of wind power generation on the GB transmission system. By focussing on the transient behaviour of a representative reduced test system following a three-phase short-circuit fault occurring on one of the two double-circuits constituting the B6 boundary, the impacts on the transient stability margins are qualitatively identified. There is a pressing necessity for new wind farms to be able to mitigate, as much as possible, their own negative impacts on system stability margins. The transient stability improvement achieved by tailoring the low voltage ride-through reactive power control response of wind farms is first investigated, and a novel control technique is then presented which can significantly mitigate the erosion of the transient stability performance of power systems, in the presence of in-creasing amounts of wind power, by tailoring the immediate post-fault active power recovery ramp-rates of the wind power plants around the system. The impacts of these control techniques on critical fault clearing times and power transfer limits are investigated. In particular, it has been found that the use of slower active power recovery from wind farms located in exporting regions when a short circuit fault occurs on the export corridor will provide significant benefits for both of these metrics, while a faster active power recovery in importing regions will provide a similar transient stability benefit. However, it is also shown that there are potential detrimental effects for system frequency stability. In addition, important impacts of wind farm settings in respect of low voltage ride through are revealed whereby the LVRT controls can act to erode stability margins if careful consideration of their settings is not taken. Assuming a future power system with high levels of centralised observability and controllability (or decentralised co-operative control systems), it may be possible to continually “dispatch” the reactive power gains and active power recovery ramp rates discussed in this thesis to match the current system setpoint and to seek an optimal transient response to a range of credible contingencies

Internal agent states : experiments using the swarm leader concept

In recent years, an understanding of the operating principles and stability of natural swarms has proven to be a useful tool for the design and control of artificial robotic agents. Many robotic systems, whose design or control principals are inspired by behavioural aspects of real biological systems such as leader-follower relationship, have been developed. We introduced an algorithm which successfully enhances the navigation performance of a swarm of robots using the swarm leader concept. This paper presents some applications based on that work using the simulations and experimental implementation using a swarming behaviour test-bed at the University of Strathclyde. Experimental and simulation results match closely in a way that confirms the efficiency of the algorithm as well as its applicability

ALMA Observations of Asymmetric Molecular Gas Emission from a Protoplanetary Disk in the Orion Nebula

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of molecular line emission from d216-0939, one of the largest and most massive protoplanetary disks in the Orion Nebula Cluster (ONC). We model the spectrally resolved HCO$^+$ (4--3), CO (3--2), and HCN (4--3) lines observed at 0\farcs5 resolution to fit the temperature and density structure of the disk. We also weakly detect and spectrally resolve the CS (7--6) line but do not model it. The abundances we derive for CO and HCO$^+$ are generally consistent with expected values from chemical modeling of protoplanetary disks, while the HCN abundance is higher than expected. We dynamically measure the mass of the central star to be $2.17\pm0.07\,M_\odot$ which is inconsistent with the previously determined spectral type of K5. We also report the detection of a spatially unresolved high-velocity blue-shifted excess emission feature with a measurable positional offset from the central star, consistent with a Keplerian orbit at $60\pm20\,\mathrm{au}$. Using the integrated flux of the feature in HCO$^+$ (4--3), we estimate the total H$_2$ gas mass of this feature to be at least $1.8-8\,M_\mathrm{Jupiter}$, depending on the assumed temperature. The feature is due to a local temperature and/or density enhancement consistent with either a hydrodynamic vortex or the expected signature of the envelope of a forming protoplanet within the disk.Comment: 19 pages, 12 figures, accepted for publication in A

Can innovations in agri-food systems deliver gender equity and resilience?

Agri-food systems constitute a huge proportion of global jobs and economies, but are failing to provide healthy diets, equitable livelihoods and sustainable practices. Women in rural areas are highly prominent in the sector and most vulnerable to climate impacts. Co-designing and bundling innovations could offer significant opportunities to achieve better outcomes. We reviewed the evidence base to explore how social and technical innovations can contribute to household resilience and gender equality. The findings suggest that combining different types of sociocultural and technical innovations into bundles (STIBs) offer a promising way forward, if they are appropriate for the context. This briefing provides a framework for agri-food practitioners to implement STIBs across contexts, stressing the importance of participative processes and understanding the contextual gender dynamics to build household resilience. Highlighting a huge evidence gap, the study calls for stronger evaluation and learning mechanisms and greater investment in rigorous, longitudinal studies

Spitzer Observations of the HII Region NGC 2467: An Analysis of Triggered Star Formation

We present new Spitzer Space Telescope observations of the region NGC 2467, and use these observations to determine how the environment of an HII region affects the process of star formation. Our observations comprise IRAC (3.6, 4.5, 5.8, and 8.0 um) and MIPS (24 um) maps of the region, covering approximately 400 square arcminutes. The images show a region of ionized gas pushing out into the surrounding molecular cloud, powered by an O6V star and two clusters of massive stars in the region. We have identified as candidate Young Stellar Objects (YSOs) 45 sources in NGC 2467 with infrared excesses in at least two mid-infrared colors. We have constructed color-color diagrams of these sources and have quantified their spatial distribution within the region. We find that the YSOs are not randomly distributed in NGC 2467; rather, over 75% of the sources are distributed at the edge of the HII region, along ionization fronts driven by the nearby massive stars. The high fraction of YSOs in NGC 2467 that are found in proximity to gas that has been compressed by ionization fronts supports the hypothesis that a significant fraction of the star formation in NGC 2467 is triggered by the massive stars and the expansion of the HII region. At the current rate of star formation, we estimate at least 25-50% of the total population of YSOs formed by this process.Comment: Accepted to the Astrophysical Journal, set to appear in Volume 701; 18 pages, 13 figures, 4 tables. This version reflects a few major changes made in the accepted version, including new figure

Portable gas chromatography–mass spectrometry method for the in‑feld screening of organic pollutants in soil and water at pollution incidents

Environmental pollution incidents generate an emergency response from regulatory agencies to ensure that the impact on the environment is minimised. Knowing what pollutants are present provides important intelligence to assist in determining how to respond to the incident. However, responders are limited in their in-feld capabilities to identify the pollutants present. This research has developed an in-feld, qualitative analytical approach to detect and identify organic pollutants that are commonly detected by regulatory environmental laboratories. A rapid, in-feld extraction method was used for water and soil matrices. A coiled microextraction (CME) device was utilised for the introduction of the extracted samples into a portable gas chromatography–mass spectrometry (GC–MS) for analysis. The total combined extraction and analysis time was approximately 6.5 min per sample. Results demonstrated that the in-feld extraction and analysis methods can screen for ffty-nine target organic contaminants, including polyaromatic hydrocarbons, monoaromatic hydrocarbons, phenols, phthalates, organophosphorus pesticides, and organochlorine pesticides. The method was also capable of tentatively identifying unknown compounds using library searches, signifcantly expanding the scope of the methods for the provision of intelligence at pollution incidents of an unknown nature, although a laboratory-based method was able to provide more information due to the higher sensitivity achievable. The methods were evaluated using authentic casework samples and were found to be ft-for-purpose for providing rapid in-feld intelligence at pollution incidents. The fact that the in-feld methods target the same compounds as the laboratory-based methods provides the added beneft that the in-feld results can assist in sample triaging upon submission to the laboratory for quantitation and confrmatory analysis