Microgrids

Integration of renewable energy sources in the electrical power system is key for enabling the decarbonization of that system. The connection of renewable generation to the electrical system is being performed in a centralized form (large renewable power plants like wind or solar power plants connected at the transmission system) and in a decentralized manner (through the connection of dispersed generation connected at the distribution system). The connection of renewable generation at distribution levels, together with other generating sources as well as energy storage systems (the so-called DER, Distributed Energy Resources) close to consumption sites, is promoting the development of microgrids: DER installations that have the capability to operate grid connected and grid isolated. The uncertainty and variability of the renewable energy sources that integrate microgrids, as well as the need for coordination with other energy sources, pose challenges in the operation, protection, control, and planning of microgrids. The five selected papers published in this Special Issue propose solutions to address these challenges.Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.1 - Per a 2030, garantir l’accés universal a serveis d’energia assequibles, confiables i modernsObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energiaPostprint (published version

Special issue on microgrids

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Optimització del transport d’energia elèctrica en sistemes multiterminal HVDC per grans parcs eòlics marins

Premi al millor Projecte de Fi de Carrera presentat durant l'any 2011 en l'àmbit d'Innovació en Energia Elèctrica que atorga la CÀTEDRA ENDESAAquest projecte estudia els sistemes multiterminal VSC-HVDC per transmissió submarina. En la primera part del projecte, aplicant tècniques d’optimització, es proposa una metodologia per minimitzar les pèrdues per efecte Joule associades a la transmissió d’energia elèctrica en una xarxa multiterminal VSC-HVDC (Voltage Source Converter - High Voltage Direct Current) que uneix els parcs eòlics marins amb les subestacions de la xarxa terrestre. L’algorisme de control dissenyat es compara amb el control droop (la solució clàssica). Finalment, s’implementen els dos esquemes de control en un cas particular de xarxa multiterminal i es realitzen simulacions amb MATLAB Simulink R per complementar l’estudi estàtic amb el dinàmic. La segona part del projecte es centra en la modelització, control i simulació d’un sistema multiterminal de quatre nodes amb el software DIgSILENT Power Factory R . S’estudia com respon el sistema en condicions normals de funcionament i sota faltes com un sot de tensió en la xarxa d’alterna o una eventual desconnexió d’un convertidor del costat xarxa.Award-winnin

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

Consecuencias de los robos de las puestas a tierras en las redes de distribución de media y baja tensión

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Short circuit analysis of an offshore AC network having multiple grid forming VSC-HVDC links

This article presents the short circuit analysis of an offshore AC network which consists of wind power plants interconnected using HVAC cables. The power generated in the offshore AC network is transmitted to several onshore grids using VSC-HVDC system. The offshore AC network is formed by the VSC-HVDC systems using frequency and voltage droop control. A coordinated control scheme is proposed for wind turbines and offshore VSCs during short circuit conditions in the offshore grid to ensure fault ride through (FRT) without compromising the system stability. The theoretical analysis used for developing this control scheme allows to calculate the system limits taking into consideration the active and reactive power capability. In order to verify the proposed control scheme, three phase symmetric faults have been applied on a wind turbine busbar, HVAC busbar, and at the AC cable that interconnects the VSC-HVDC system. Additionally, a frequency coordination control scheme without communication between wind power generation and VSC-HVDC system has been proposed. The methodology and control system have been validated by performing a nonlinear simulation.Postprint (author's final draft

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

Potential benefits of distributed generation in the reduction of non-technical losses

Power generation at or near the consumers can affect citizens positively, especially those who belong to social classes with low earnings. This article proposes an analysis of potential economic and technical benefits that the insertion of Distributed Generation (DG) in low-income communities can create, including the reduction of commercial losses, and alternatives to allow viable financing.Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantPostprint (published version

Optimal operation of DC networks to support power system outage management

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The penetration of dc networks for different applications in power systems is increasing. This paper presents a novel methodology for security-constrained optimal power flow (SCOPF) operation of a power system, such as a smart grid or a supergrid, with an embedded dc network. The methodology demonstrates that dc networks can be operated to provide support to ac systems, increasing its security of supply and resilience in case of outages, while reducing operational costs. Moreover, the outage management support can be achieved via a preventive SCOPF – i.e. the combined network stays N-1 secure after outages without need for further control action – or via a corrective SCOPF, by using the fast controls of the ac-dc converters to react to the contingencies. The methodology relies on the construction of a binary outage matrix and optimizes only the control variables of the ac and dc networks. It was successfully tested in system with 12 buses and in the IEEE30 network with 35 buses. Operational savings of up to 1% and 0.52% were obtained for the first and second networks, respectively, while network violations for the N-1 contingency scenarios were completely eliminated in the first and reduced by 70% in the former.Postprint (author's final draft

Superredes, las redes eléctricas del futuro

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