Design of Ancillary Services for Battery Energy Storage Systems to Mitigate Voltage Unbalance in Power Distribution Networks

power system, voltage unbalance issues are expected to exacerbate. Single{phase connectedphotovoltaic (PV) panels may cause unequal three{phase power ows, resultingin unbalanced grid currents and voltages. In addition, the random charging behaviour ofPlug{in Hybrid Electric Vehicles (PHEVs) equipped with single{phase on{board chargersis expected to further contribute to voltage unbalance rise as the number of thesedevices grows. If voltage unbalance increases to unacceptable levels, it may have adverseeects on power system operation and on the equipment connected to it. Traditionally,the phase swapping technique has been deployed by distribution system operators forvoltage unbalance mitigation, while other mitigating techniques include the deploymentof power electronics-based devices. The majority of the devices reported in the literatureare based on three-phase congurations, including series and parallel active power lters,unied power quality conditioners (UPQCs), static synchronous compensators (STATCOMs)and, more recently, three-phase distributed generation (DG) inverters.This research proposes the use of single-phase battery energy storage systems (BESSs)for the provision of phase balancing services, which has been considered only in a few literatureworks, with most of these research papers focusing on three-phase BESSs. In thisthesis, a novel control strategy is proposed for single-phase BESS units to compensatevoltage unbalance by injecting both active and reactive power simultaneously. The proposedapproach is based on the coordinated operation of three independent single-phaseBESS inverters using local voltage and current measurements.Initially, a comprehensive literature review is performed with the following aims: arobust classication of the ancillary services currently oered by BESSs, harmonisation ofthe notation found in the literature for ancillary services, and identication of potentialfuture applications of BESSs to power grids with large number of Low Carbon Technologies(LCTs). Then, the eectiveness of the proposed voltage unbalance compensationmethod is validated in the simulation environment, where two realistic models of distributionsystems are developed. Next, the impact of increasing PV and EV penetrationlevels on voltage unbalance for a typical UK distribution system is assessed based on adeterministic approach. The control strategy is validated experimentally by carrying outHardware-In-The-Loop (HIL) tests. Finally, an equivalent model of the distribution systemand BESS inverter is derived, which allows to carry out a preliminary probabilisticstudy to cater for the uncertainties related to the location and size of the PVs and EVs,and to evaluate the voltage unbalance levels without and with the BESSs controlled toprovide voltage unbalance compensation.It is concluded that the proposed BESS control system may eectively reduce thevoltage unbalance levels under various loading and generating conditions

Battery Energy Storage Systems in the United Kingdom: A Review of Current State-of-the-Art and Future Applications

The number of battery energy storage systems (BESSs) installed in the United Kingdom and worldwide is growing rapidly due to a variety of factors, including technological improvements, reduced costs and the ability to provide various ancillary services. The aim of this paper is to carry out a comprehensive literature review on this technology, its applications in power systems and to identify potential future developments. At first, the main BESSs projects in the UK are presented and classified. The parameters provided for each project include rated power, battery technology and ancillary services provided, if any. In the next section, the most commonly deployed ancillary services are classified and described. At the same time, the nomenclature found in the literature is explained and harmonised. The second part of the paper focuses on future developments and research gaps: ancillary services that currently are not common but that are likely to be deployed more widely in the future will be described, and more general research topics related to the development of BESSs for power system applications will be outlined

CERN

As a team, we decided to elaborate on the CERN center for scientific research. We are going to refer to topics such as; the history of the institute, the countries that have participated in the foundation of CERN, the main projects that take place there and lastly the contribution of our country, Greece,  in the scientific research taking place there.

Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes

In this thesis results are described with the aim of examining the optoelectronic properties of InAs/GaAs columnar quantum-dots and comparing them with those of more conventional self-assembled quantum-dots. The polarisation properties of a set of columnar quantum-dot samples — of varied aspect ratio and In compositional contrast between the rod-shaped dot and the surrounding 2-D layer — are studied. For this investigation a new method to obtain the ratio of the fundamental TE/TM optical response using edge photo-absorption spectroscopy is proposed, which corrects for the polarisation-dependent features of the experimental set-up. The method is verified by application to compressive and tensile strained InGaP quantum well structures, where the results are in agreement with known ratios of the band-edge matrix elements. When applied to columnar quantum-dot samples it is shown that the TE/TM optical response depends on the dot aspect ratio and the In compositional contrast. A polarisation-independent photo-absorption is illustrated for a columnar quantum-dot of an aspect ratio (dot's height over diameter) 3.51:1, which is desired for use in semiconductor optical amplifiers. For the columnar dot of an extremely high aspect ratio, 7.5:1, a room temperature TM-dominant polarisation lasing emission is observed. By studying the Quantum-Confined Stark Effect, a dramatic enhancement of the Stark shift amplitude is shown for columnar quantum-dot samples of an increased dot aspect ratio from 0.63:1 up to 1.12:1, which may have application in optical modulation/switching. For a higher aspect ratio columnar quantum-dot the shift of the band edge of the photo-absorption spectra is reduced dramatically and this has been attributed to an overall effect where the observable shift becomes the result of higher energy transitions, where their oscillator strength change very rapidly within the studied range of field. For the highest aspect ratio dot, i.e. of aspect ratio 10:1, there is no any observable shift.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes

In this thesis results are described with the aim of examining the optoelectronic properties of InAs/GaAs columnar quantum-dots and comparing them with those of more conventional self-assembled quantum-dots. The polarisation properties of a set of columnar quantum-dot samples — of varied aspect ratio and In compositional contrast between the rod-shaped dot and the surrounding 2-D layer — are studied. For this investigation a new method to obtain the ratio of the fundamental TE/TM optical response using edge photo-absorption spectroscopy is proposed, which corrects for the polarisation-dependent features of the experimental set-up. The method is verified by application to compressive and tensile strained InGaP quantum well structures, where the results are in agreement with known ratios of the band-edge matrix elements. When applied to columnar quantum-dot samples it is shown that the TE/TM optical response depends on the dot aspect ratio and the In compositional contrast. A polarisation-independent photo-absorption is illustrated for a columnar quantum-dot of an aspect ratio (dot's height over diameter) 3.51:1, which is desired for use in semiconductor optical amplifiers. For the columnar dot of an extremely high aspect ratio, 7.5:1, a room temperature TM-dominant polarisation lasing emission is observed. By studying the Quantum-Confined Stark Effect, a dramatic enhancement of the Stark shift amplitude is shown for columnar quantum-dot samples of an increased dot aspect ratio from 0.63:1 up to 1.12:1, which may have application in optical modulation/switching. For a higher aspect ratio columnar quantum-dot the shift of the band edge of the photo-absorption spectra is reduced dramatically and this has been attributed to an overall effect where the observable shift becomes the result of higher energy transitions, where their oscillator strength change very rapidly within the studied range of field. For the highest aspect ratio dot, i.e. of aspect ratio 10:1, there is no any observable shift

High quality factor nitride-based optical cavities: microdisks with embedded GaN/Al(Ga)N quantum dots

We compare the quality factor values of the whispery gallery modes of microdisks incorporating GaN quantum dots (QDs) grown on AlN and AlGaN barriers by performing room temperature photoluminescence (PL) spectroscopy. The PL measurements show a large number of high Q factor (Q) resonant modes on the whole spectrum which allows us to identify the different radial mode families and to compare them with simulations. We report a considerable improvement of the Q factor which reflect the etching quality and the relatively low cavity loss by inserting QDs into the cavity. GaN/AlN QDs based microdisks show very high Q values (Q > 7000) whereas the Q factor is only up to 2000 in microdisks embedding QDs grown on AlGaN barrier layer. We attribute this difference to the lower absorption below bandgap for AlN barrier layers at the energies of our experimental investigation

Strain evolution in GaN Nanowires: from free-surface objects to coalesced templates

Top-down fabricated GaN nanowires, 250 nm in diameter and with various heights, have been used to experimentally determine the evolution of strain along the vertical direction of 1-dimensional objects. X-ray diffraction and photoluminescence techniques have been used to obtain the strain profile inside the nanowires from their base to their top facet for both initial compressive and tensile strains. The relaxation behaviors derived from optical and structural characterizations perfectly match the numerical results of calculations based on a continuous media approach. By monitoring the elastic relaxation enabled by the lateral free-surfaces, the height from which the nanowires can be considered strain-free has been estimated. Based on this result, NWs sufficiently high to be strain-free have been coalesced to form a continuous GaN layer. X-ray diffraction, photoluminescence and cathodoluminescence clearly show that despite the initial strain-free nanowires template, the final GaN layer is strained

Fabrication and Optical Properties of a Fully Hybrid Epitaxial ZnO-Based Microcavity in the Strong Coupling Regime

In order to achieve polariton lasing at room temperature, a new fabrication methodology for planar microcavities is proposed: a ZnO-based microcavity in which the active region is epitaxially grown on an AlGaN/AlN/Si substrate and in which two dielectric mirrors are used. This approach allows as to simultaneously obtain a high-quality active layer together with a high photonic confinement as demonstrated through macro-, and micro-photoluminescence ({\mu}-PL) and reflectivity experiments. A quality factor of 675 and a maximum PL emission at k=0 are evidenced thanks to {\mu}-PL, revealing an efficient polaritonic relaxation even at low excitation power.Comment: 12 pages, 3 figure

Real-World Chaos-Based Cryptography Using Synchronised Chua Chaotic Circuits

This work presents the hardware demonstrator of a secure encryption system based on synchronised Chua chaotic circuits. In particular, the presented encryption system comprises two Chua circuits that are synchronised using a dedicated bidirectional synchronisation line. One of them forms part of the transmitter, while the other of the receiver. Both circuits are tuned to operate in a chaotic mode. The output (chaotic) signal of the first circuit (transmitter) is digitised and then combined with the message to be encrypted, through an XOR gate. The second Chua circuit (receiver) is used for the decryption; the output chaotic signal of this circuit is similarly digitised and combined with the encrypted message to retrieve the original message. Our hardware demonstrator proves that this method can be used in order to provide extremely lightweight real-world, chaos-based cryptographic solutions.Comment: This work was accepted for and presented as a hardware demo at the 2022 IEEE International Symposium on Hardware Oriented Security and Trust (HOST 2022), held from 27 to 30 June 2022, in Washington, DC, US