Protección contra sobretensiones por descargas atmosféricas a tierra mediante

Las redes de distribuci on (de media tensi on), encargadas de distribuir la energ a el ectrica desde la red de transporte hasta el usuario nal, est an sujetas a perturbaciones que pueden afectar a la calidad de la energ a el ectrica suministrada. Cuando los equipos y la aparamenta de estas redes son afectados por sobretensiones provocadas por descargas atmosf ericas, pueden producirse da~nos que afectan a todo el sistema de distribuci on y por lo tanto a los usuarios nales. Por esta raz on, la aparamenta y los equipos de las redes de distribuci on suelen protegerse con descargadores de sobretensi on o pararrayos. Sin embargo, los niveles de sobretensi on producidos por los rayos en redes a ereas son extremadamente elevados por lo que se producen faltas en los aisladores que son despejadas, en el mejor de los casos, por los elementos de protecci on. Como consecuencia, los usuarios nales pueden verse afectados viendo huecos de tensi on, una calidad de onda afectada o interrupciones del servicio.En los ultimos a~nos, con el incremento del n umero de cargas sensibles conectadas al sistema el ectrico, las p erdidas econ omicas por las sobretensiones producidas por rayos pueden ser importantes por lo que cada vez es m as com un proteger, adem as de los equipos conectados, los aisladores de la red. De esta forma, por un lado es posible evitar que un rayo afecte a la calidad de suministro de los clientes y por otro, los aislamientos de la red se ven menos deteriorados obteniendo en un bene cio econ omico. En este proyecto se ha implementado una metodolog a para realizar una previsi on del n umero de contorneos producidos por las descargas atmosf ericas en las proximidades de las redes de distribuci on. Posteriormente, se ha desarrollado, mediante algoritmos gen eticos, un m etodo para la optimizaci on del n umero y ubicaci on de los pararrayos teniendo en cuenta las perturbaciones producidas por rayos indirectos. La optimizaci on se realiza a partir de la valoraci on econ omica de los bene cios de instalar pararrayos (valorados a partir de la disminuci on de la energ a no suministrada y del coste de la inversi on) de manera que a partir de un conjunto de posibles soluciones generadas de forma aleatoria, mediante un proceso iterativo, se generan nuevas soluciones con caracter sticas similares (n umero de pararrayos y ubicaci on) a las mejores soluciones de la iteraci on anterior. De esta forma, en cada iteraci on se tiene un escenario mejor adaptado a la funci on objetivo. Finalmente, la metodolog a desarrollada se ha simulado a una red de distribuci on

Feeder flow control and operation in large scale photovoltaic power plants and microgrids : Part I Feeder ow control in large scale photovoltaic power plants : Part II Multi-microgrids and optimal feeder ow operation of microgrids

This thesis deals with the integration of photovoltaic energy into the electrical grid. For this purpose, two main approaches can be identified: the interconnection of large scale photovoltaic power plants with the transmission network, and the interconnection of small and medium-scale photovoltaic installations with the distribution network. The first part of the thesis is focussed on the interconnection of large scale photovoltaic power plants. Large scale photovoltaic power plants are required to provide different ancillary services to the electrical networks. For this purpose, it is necessary to control the active and reactive power injected by photovoltaic power plants at the point of interconnection, i.e. to control the power flow through the main feeder. In this direction, it is developed a central controller capable of coordinating the different devices of the photovoltaic power plants as photovoltaic inverters, FACTS, capacitor banks and storage. The second part is focused on the distributed generation, consisting on small and medium-scale generation facilities connected to the distribution system. In this context, distribution grids, traditionally operated as passive systems, become active operated systems. In this part, the microgrid concept is analysed, which is one of the most promising solutions to manage, in a coordinated manner, the different distributed energy resources. Taking into account the possible transformation of the current distribution system to a multi-microgrid based system, the different architectures enabling microgrids interconnections are analysed. For the multi-microgrid operation, it could result interesting that a portion of their networks operate so that the power exchange is maintained constant, i.e. controlling the power flow at the main feeder. In this thesis, an optimal power flow problem formulation for managing the distributed generation of these feeder flow controlled microgrids is proposed

Feeder flow control and operation in large scale photovoltaic power plants and microgrids : Part I Feeder ow control in large scale photovoltaic power plants : Part II Multi-microgrids and optimal feeder ow operation of microgrids

Premi extraordinari doctorat UPC curs 2017-2018. Àmbit d’Enginyeria IndustrialThis thesis deals with the integration of photovoltaic energy into the electrical grid. For this purpose, two main approaches can be identified: the interconnection of large scale photovoltaic power plants with the transmission network, and the interconnection of small and medium-scale photovoltaic installations with the distribution network. The first part of the thesis is focussed on the interconnection of large scale photovoltaic power plants. Large scale photovoltaic power plants are required to provide different ancillary services to the electrical networks. For this purpose, it is necessary to control the active and reactive power injected by photovoltaic power plants at the point of interconnection, i.e. to control the power flow through the main feeder. In this direction, it is developed a central controller capable of coordinating the different devices of the photovoltaic power plants as photovoltaic inverters, FACTS, capacitor banks and storage. The second part is focused on the distributed generation, consisting on small and medium-scale generation facilities connected to the distribution system. In this context, distribution grids, traditionally operated as passive systems, become active operated systems. In this part, the microgrid concept is analysed, which is one of the most promising solutions to manage, in a coordinated manner, the different distributed energy resources. Taking into account the possible transformation of the current distribution system to a multi-microgrid based system, the different architectures enabling microgrids interconnections are analysed. For the multi-microgrid operation, it could result interesting that a portion of their networks operate so that the power exchange is maintained constant, i.e. controlling the power flow at the main feeder. In this thesis, an optimal power flow problem formulation for managing the distributed generation of these feeder flow controlled microgrids is proposed.La present tesi tracta de la integració d'energia fotovoltaica en xarxes elèctriques. Per a tal finalitat, es poden identificar dues grans tendències en l'actualitat: la interconnexió de grans plantes de generació en la xarxa de transport (alta tensió), i la interconnexió de petites i mitjanes instal·lacions en la xarxa de distribució (mitja i baixa tensió). La primera part s'enfoca a la interconnexió de grans plantes de generació fotovoltaica. Degut als canvis dels darrers anys en el mix de generació elèctrica, les grans plantes de generació fotovoltaica es veuen obligades a donar diversos serveis de suport a les xarxes elèctriques. Per a aquesta finalitat, resulta necessari controlar la potencia activa i reactiva que la planta injecta en el punt de connexió, és a dir, controlar la potencia en la línia d’alimentació principal, feeder. En aquest sentit, es desenvolupa un controlador central capaç de coordinar els diferents elements de les plantes fotovoltaiques com els inversors fotovoltaics, FACTS, bancs de condensadors i bateries d'emmagatzematge. La segona part s'enfoca a l'anomenada generació distribuïda, de la que formen part les petites instal·lacions generadores connectades a la xarxa de distribució. En aquest context, aquestes xarxes passen de ser operades de forma passiva a forma activa. En aquesta part s'analitza el concepte de microxarxa, una de les solucions més prometedores per gestionar els diferents recursos distribuïts. Donat que es pot esperar una transformació del sistema de distribució actual a un sistema basat en multi-microxarxes, s'analitzen les diferents arquitectures amb les quals aquestes es poden interconnectar. Per la operació de multi-microxarxes pot resultar interessant que algunes microxarxes operin de forma que la potencia intercanviada amb la xarxa externa sigui constant, és a dir, controlant el flux de potencia de la línia d’alimentació principal. En aquesta tesi es realitza la formulació d'un problema d’optimització de fluxos de potencia per gestionar la generació distribuïda d'aquestes microxarxes.Award-winningPostprint (published version

Active power control in a hybrid PV-storage power plant for frequency support

The recent increase of intermittent power generation plants connected to the electric power grids may stress the operation of power systems. So, grid codes started considering these power plants should con- tribute to the grid support functions. Recently, a power ramp rate limitation is being included in several grid codes, which is a challenge for photovoltaic installations due to the lack of inertia. This paper pre- sents a method to deal with the main grid code requirements considering a PV plant with an energy stor- age device, where a strict two-second time window ramp rate restriction is applied. A direct ramp rate control strategy is used, which includes a dynamic SOC control and battery support functionality for active power setpoint compliance. The control strategy is validated by simulations.Postprint (published version

Capability curve analysis of photovoltaic generation systems

The present article assesses the study of the PV generator capability curves for use in large scale photovoltaic power plants (LS-PVPPs). For this purpose, the article focuses on three main aspects: (i) the modelling of the main components of the PV generator, (ii) the operational limits analysis of the PV array together with the inverter, and (iii) the capability curve analysis considering variable solar irradiance and temperature. To validate this study a PVPP of 1 MW is designed, modelled and simulated in DIgSILENT PowerFactory®. The results for each case scenario shows that the capability curve and the limitations are directly affected by: the solar irradiance, temperature, dc voltage, and the modulation index.Peer ReviewedPostprint (author's final draft

Active and reactive power control of a PV generator for grid code compliance

As new grid codes have been created to permit the integration of large scale photovoltaic power plants into the transmission system, the enhancement of the local control of the photovoltaic (PV) generators is necessary. Thus, the objective of this paper is to present a local controller of active and reactive power to comply the new requirements asked by the transmission system operators despite the variation of ambient conditions without using extra devices. For this purpose, the control considers the instantaneous capability curves of the PV generator which vary due to the change of solar irradiance, temperature, dc voltage and modulation index. To validate the control, the PV generator is modeled in DIgSILENT PowerFactoryr and tested under different ambient conditions. The results show that the control developed can modify the active and reactive power delivered to the desired value at different solar irradiance and temperature.Postprint (published version

Electrical Grids Based on Power Routers: Definition, Architecture and Modeling

Recent studies have developed a power electronic device known as the power router, able to fully control the power flows over the connected power lines. The present paper aims to extend the application of power routers to an electrical grid and explore its characteristics and limitations. It defines the power router grid concept, including the conditions for interconnection and architecture; it proposes a mathematical modelling methodology, analyses its operational requirements, and explores the degree of flexibility the proposed grid architecture provides. Finally, two case studies are presented to show the application of the power router grid in a practical example.Peer ReviewedPostprint (published version

Topologies for large scale photovoltaic power plants

© 2016 Elsevier Ltd. All rights reserved. The concern of increasing renewable energy penetration into the grid together with the reduction of prices of photovoltaic solar panels during the last decade have enabled the development of large scale solar power plants connected to the medium and high voltage grid. Photovoltaic generation components, the internal layout and the ac collection grid are being investigated for ensuring the best design, operation and control of these power plants. This paper addresses the review of components as photovoltaic panels, converters and transformers utilized in large scale photovoltaic power plants. In addition, the distribution of these components along this type of power plant and the collection grid topologies are also presented and discussed.Peer ReviewedPostprint (author's final draft

Optimal feeder flow control for grid connected microgrids

The optimal management of distributed energy resources is one of theexisting challenges for the deployment of microgrids. When microgrids op-erate under feeder flow control mode, trying to maintain a constant self-consumption, generators adapt their output power to compensate load andnon-dispatchable generation variations. So, due to the uncertainty, findingthe optimal operation point is an important task that can become complex.This paper proposes an optimal power flow problem formulation for feederflow controlled microgrids. It is formulated as a mixed integer second ordercone program considering the optimal power flow equations in its relaxedform and uncertainty by means of stochastic formulation. In addition, analgorithm is developed in order to find a feasible optimum solution of theoriginal non-relaxed problem. The proposed algorithm can also be used inother optimal power flow problems with the condition that they must usethe same relaxation. The algorithm is validated through the IEEE 33-Busdistribution test system.Postprint (author's final draft

Analytical and Normalized Equations to Implement the Optimized Triple Phase-Shift Modulation Strategy for DAB Converters

A fully normalized algorithm to implement the optimal triple-phase-shift (TPS) modulation strategy of the dual active bridge (DAB) converter is proposed in this article. The algorithm evaluates three simple expressions that fit the optimal solutions obtained in recent works, which allows the algorithm to be implemented in real-time and valid for the whole operating range. As a result, the converter operates under zero voltage switching (ZVS) conditions and minimizes conduction losses. In addition, the algorithm considers the minimum current required to guarantee the ZVS condition that faces the undesired dead-band of switching devices effect. The proposal achieves a soft transition between any operation region and a fast closedloop response with no stability concern, presenting robustness under leakage inductance deviation. Finally, the algorithm presented in this article is verified with a 4-kW experimental prototype. Experimental results show that the algorithm proposed can be evaluated with less than 2.8 µs and allows soft transition between any operation region to be achieved. Besides, fast closedloop changes of 750 µs through all the operating ranges, keeping minimum rms current under ZVS, are shownPeer ReviewedPostprint (published version