Rise of the global environmental awareness and climate change impacts caused by greenhouse gases emissions brings about a revolution in the power and energy industries to reduce fossil fuels and promote low-carbon and renewable distributed generation (DG). The new dimensions, mainly encouraged by the governments’ legislative targets and incentives, have allowed the development of DG worldwide. In the U.K., renewable DG especially wind is being connected on distribution networks and ranges widely in scales. Despite the growing number of potential DG sites, the surplus generation present on the passive networks can lead to some technical problems. In particular, rural networks where wind farms exist are prone to voltage rise and line thermal constraints. In order to accommodate new DG and ensure security of supply and network reliability, active management to mitigate these issues are required. In addition, the duties to provide cost-effective DG connections at avoided expensive investment incurred from conventional solutions, e.g., reinforcement and maintain robust network are a major challenge for Distribution Network Operators (DNOs). This thesis endeavours to develop an adaptive control scheme that provides local and real-time management against voltage variations and line capacity overload at the point of wind connections on rural distribution networks. Taking into account maximising power exports and providing an economically-viable control scheme, the wind turbine’s capability, comprising reactive power control and active power curtailment, is used. Whilst the thesis concentrates on the decentralised control applying several different algorithms, in addition, semi-coordinated and centralised approaches that adopt on-load tap changing transformers’ regulation and Optimal Power Flow tool are developed. Comparisons of these approaches based upon measures, i.e., economics, DG penetration and performance are determined. As an outcome, the developed scheme can enable growing integration of renewable DG on distribution networks and can be seen as an interim solution for the DNOs towards Smart Distribution Networks.

Σκοπός της παρούσης διπλωματικής εργασίας είναι η μελέτη μεθόδων περιορισμού των ανυψώσεων τάσης σε δίκτυα διανομής με διεσπαρμένη παραγωγή. Η μελέτη περιλαμβάνει αρχικά την ανάλυση και την εξήγηση του φαινομένου της ανύψωσης της τάσης σε δίκτυα διανομής στα οποία έχουν εγκατασταθεί τεχνολογίες διεσπαρμένης παραγωγής. Στη συνέχεια αναλύονται οι μέθοδοι αντιμετώπισης αυτού του φαινομένου. Συγκεκριμένα αναλύεται η μέθοδος περιορισμού της αύξησης της τάσης μέσω περιορισμού της ενεργού ισχύος των τεχνολογιών διεσπαρμένης παραγωγής ή μέσω απορρόφησης άεργου ισχύος ή ακόμη και μέσω συντονισμένου ελέγχου Μ/Σ μεταβλητής λήψης. Αναλύεται επίσης μέθοδος η οποία βασίζεται στη χρήση των Multiagent Systems. Επειδή όμως κεντρικές προσεγγίσεις απαιτούν σημαντικές επενδύσεις σε αισθητήρες, επικοινωνιακά και ελεγκτικά συστήματα , γεγονός που καθιστά την εφαρμογή τους σε μεγάλο αριθμό τεχνολογιών διεσπαρμένης παραγωγής δύσκολη, προτείνεται μία μέθοδος κατανεμημένου ελέγχου της τάσης. Προτείνονται ακόμη και πιο περίπλοκες μέθοδοι ελέγχου, όπως η ρύθμιση της τάσης που τίθεται ως στόχος από τους αυτόματους ελεγκτές τάσης ή ακόμη και συνδυασμός σταθερού συντελεστή ισχύος με αυτόματο έλεγχο της τάσης. Τέλος, αναλύεται μία μέθοδος ελέγχου της τάσης ενός αιολικού πάρκου μέσω δύο επιπέδων ελέγχου: ενός εποπτικού συστήματος ελέγχου όλου του πάρκου και ενός συστήματος ελέγχου κάθε ανεμογεννήτριας ξεχωριστά. Στη συνέχεια μελετήθηκε μία μέθοδος η οποία έχει ως στόχο της να μην ελέγχει την τάση του ζυγού της διεσπαρμένης παραγωγής αλλά να εξασφαλίζει ότι οι εγχύσεις ισχύος από μόνες τους δεν προκαλούν σημαντικές διαταραχές στην τάση. Αυτό γίνεται μέσω ελέγχου της άεργου ισχύος και περιλαμβάνει την εύρεση της τιμής της άεργου ισχύος που παράγει ή καταναλώνει η διεσπαρμένη γεννήτρια, τέτοιας ώστε η αύξηση της τάσης που προκαλείται από την ενεργό τιμή της γεννήτριας να ελαχιστοποιείται. Η παραπάνω μέθοδος εφαρμόζεται σε ένα ακτινικό δίκτυο ενός ζυγού για δύο περιπτώσεις, για την περίπτωση που στο ζυγό είναι συνδεδεμένο φορτίο και για την περίπτωση που δεν είναι φορτίο συνδεδεμένο. Στο ίδιο δίκτυο και για τις ίδιες περιπτώσεις εφαρμόζεται η μέθοδος σταθερού χωρητικού και επαγωγικού συντελεστή ισχύος και γίνεται σύγκριση των δύο μεθόδων. Η μέθοδος ελέγχου άεργου ισχύος εφαρμόζεται και σε ένα δίκτυο τεσσάρων ζυγών στους οποίους υπάρχουν συνδεδεμένα φορτία. / The purpose of this diploma thesis is to study approaches of voltage rise mitigation in distribution networks with distributed generation. The study at the beginning analyzes and explains the problem of voltage rise in distribution networks in which technologies of distributed generation are installed. Then approaches of mitigating this problem have been proposed. It is proposed an approach based on curtailing the active power generation. It is also suggested to mitigate voltage rise through absorption of reactive power or even through coordinated voltage control using on load tap changing transformers (OLTC). Another approach has been considered for voltage support through multi-agent-based optimization. However centralized approaches require significant investments in sensors, communication and control systems, which makes their application to massive distributed generation situations difficult to implement. Distributed voltage control approaches have also been proposed to limit the voltage rise in feeders where load and generation were considered continuously distributed. More complex distributed approaches have been proposed to control the target voltage of automatic voltage control relays at primary substations and to combine fixed power factor with automatic voltage control.Finally, a method of controlling the voltage of a wind park with two control levels is proposed: a supervisory control system throughout the park and a control system of each individual wind turbine. Then it is studied an approach that aims not to put distributed generation in control of bus voltage but to assure that injections alone do not cause significant voltage perturbations. This is achieved through a power control approach, which consists in finding the value of the generation’s reactive power such that the voltage rise caused by generation’s active power is minimized. The approach is applied to a two-bus radial network, for two load conditions: highly loaded and not loaded. In the same network is also applied a constant leading and lagging power factor approach which is compared with the previous one. The reactive power control approach is also applied to a four-bus highly loaded network.

Orientador: Antonio Padilha Feltrin / Resumo: Este trabalho apresenta uma proposta de estratégia global de controle de tensão que emprega programação não linear e duas extensões de estratégias de controle de tensão, encontrados na literatura. O principal objetivo destas estratégias é solucionar o problema de aumento de tensão nas redes de distribuição de baixa tensão, causado pela injeção de potência do gerador fotovoltaico distribuído. Estas estratégias de controle de tensão foram implementadas e analisadas a fim de verificar a sua eficácia e comparar os seus comportamentos. Para os testes, foram considerados a operação de geradores fotovoltaicos monofásicos e trifásicos distribuídos em um sistema teste de distribuição em baixa tensão. Os resultados mostraram que depois da aplicação das estratégias de controle, os perfis de tensão em regime permanente ficaram dentro da faixa de tensão permitida, obtendo-se uma mínima redução de potência ativa injetada dos geradores fotovoltaicos com os seus correspondentes fatores de potência. / Abstract: This work presents a proposal of a global voltage control strategy that use nonlinear programming and two extensions of voltage control strategies that are found in the literature. The main objective of these strategies is to solve the problem of voltage increase in low voltage distribution networks, caused by the power injection of the distributed photovoltaic generator. These voltage control strategies have been implemented and analyzed in order to verify their effectiveness and compare their behaviors. For the test, the operation of single-phase and three-phase photovoltaic generators distributed in a low voltage distribution test system were considered. The results showed that after the application of the control strategies, the steady-state voltage profiles were whihin the allowed voltage range, obtaining a minimum reduction of the active power injection of the photovoltaic generators with their corresponding powe factors. / Mestre

Submitted by JAIMIS SAJID LEON COLQUI null (jeimis.leon@gmail.com) on 2017-06-30T12:04:16Z No. of bitstreams: 1 Dissertação_Jaimis Leon_Eng_Eletrica.pdf: 1870541 bytes, checksum: cb3fb21a21d28fea6773b5e6d6b213bd (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-06-30T14:27:39Z (GMT) No. of bitstreams: 1 leoncolqui_js_me_ilha.pdf: 1870541 bytes, checksum: cb3fb21a21d28fea6773b5e6d6b213bd (MD5) / Made available in DSpace on 2017-06-30T14:27:39Z (GMT). No. of bitstreams: 1 leoncolqui_js_me_ilha.pdf: 1870541 bytes, checksum: cb3fb21a21d28fea6773b5e6d6b213bd (MD5) Previous issue date: 2017-01-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho apresenta uma proposta de estratégia global de controle de tensão que emprega programação não linear e duas extensões de estratégias de controle de tensão, encontrados na literatura. O principal objetivo destas estratégias é solucionar o problema de aumento de tensão nas redes de distribuição de baixa tensão, causado pela injeção de potência do gerador fotovoltaico distribuído. Estas estratégias de controle de tensão foram implementadas e analisadas a fim de verificar a sua eficácia e comparar os seus comportamentos. Para os testes, foram considerados a operação de geradores fotovoltaicos monofásicos e trifásicos distribuídos em um sistema teste de distribuição em baixa tensão. Os resultados mostraram que depois da aplicação das estratégias de controle, os perfis de tensão em regime permanente ficaram dentro da faixa de tensão permitida, obtendo-se uma mínima redução de potência ativa injetada dos geradores fotovoltaicos com os seus correspondentes fatores de potência. / This work presents a proposal of a global voltage control strategy that use nonlinear programming and two extensions of voltage control strategies that are found in the literature. The main objective of these strategies is to solve the problem of voltage increase in low voltage distribution networks, caused by the power injection of the distributed photovoltaic generator. These voltage control strategies have been implemented and analyzed in order to verify their effectiveness and compare their behaviors. For the test, the operation of single-phase and three-phase photovoltaic generators distributed in a low voltage distribution test system were considered. The results showed that after the application of the control strategies, the steady-state voltage profiles were whihin the allowed voltage range, obtaining a minimum reduction of the active power injection of the photovoltaic generators with their corresponding powe factors.

The Swedish Energy Agency has a target to increase solar photovoltaics (PV) power production by up to 5-10% of the total electricity demand by the year 2040. The PV potential for the residential market is high and its contribution to the total installed PV capacity is expected to increase significantly. The technical requirements should be met to keep high reliability and good power quality at the customers, therefore, it is important for planning reasons to proactively find the maximum amount PV power that can be connected at each low-voltage network without violating the performance of the grid. This amount is known as the hosting capacity. A method for PV hosting capacity estimation by taking overvoltage and transformer overload as performance indices was developed in this thesis. The method does not require any knowledge about the topology of the network. The overload hosting capacity can be estimated for any combination of customers having PV power and for the overvoltage hosting, the minimum at each penetration level can be estimated. The method was implemented on four low-voltage networks located in a typical Vattenfall medium-voltage network and the comparison of the estimation results to a power flow simulation showed good correspondence. It was shown how the impact of PV power in adjacent secondary substations can be accounted for. Using SS-EN50160 voltage limits, the studied networks were able to handle 3-7 times the PV penetration level needed (8 kWp at 20% of the customers) to achieve the national goal in Sweden without grid investments.

Orientador: Júlio Borges de Souza / Resumo: Devido a um conjunto de questões econômicas e ambientais, a geração distribuída baseada em fontes renováveis tem sido incentivada por vários países. No Brasil, a conexão de unidades de geração distribuída fotovoltaica (GDFV) às redes de distribuição de baixa tensão, por meio de unidades residenciais e comerciais, tem apresentado uma rápida expansão. Diante deste cenário, é necessário investigar os possíveis impactos negativos que tal expansão pode resultar sobre os sistemas de distribuição. Neste trabalho, busca-se avaliar o impacto sobre a tensão em regime permanente. Para se alcançar tal objetivo, utiliza-se como modelo do sistema de distribuição a rede de teste IEEE 13 barras. Através do software de acesso livre OpenDss, o qual é devidamente apresentado, o comportamento da tensão ao longo desta rede, antes e depois da inserção da GDFV, é estudado por meio de simulações pontuais e diárias. Também é analisado neste trabalho de que forma o sistema de geração distribuída fotovoltaica, através do uso do controle voltvar, pode atenuar tal impacto. / Abstract: Due to a set of economic and environmental issues, distributed generation based on renewable sources has been encouraged by several countries. In Brazil, the connection of photovoltaic distributed generation units (PVDG) to low voltage distribution networks through residential and commercial units has shown a rapid expansion. Given this scenario, it is necessary to investigate the possible negative impacts that such expansion may result on distribution systems. This work aims to evaluate the impact on the steady state voltage. To achieve this goal, the IEEE 13 bus test network is used as a model of the distribution system. Through the open access software OpenDss, which is properly presented, the behavior of the voltage along this network, before and after the insertion of the PVDG, is studied through punctual and daily simulations. It is also analyzed in this work how the photovoltaic distributed generation system, by voltvar control, can mitigate such impact. / Mestre