Ancillary Services in Hybrid AC/DC Low Voltage Distribution Networks

In the last decade, distribution systems are experiencing a drastic transformation with the advent of new technologies. In fact, distribution networks are no longer passive systems, considering the current integration rates of new agents such as distributed generation, electrical vehicles and energy storage, which are greatly influencing the way these systems are operated. In addition, the intrinsic DC nature of these components, interfaced to the AC system through power electronics converters, is unlocking the possibility for new distribution topologies based on AC/DC networks. This paper analyzes the evolution of AC distribution systems, the advantages of AC/DC hybrid arrangements and the active role that the new distributed agents may play in the upcoming decarbonized paradigm by providing different ancillary services.Ministerio de Economía y Competitividad ENE2017-84813-RUnión Europea (Programa Horizonte 2020) 76409

Simplified model of battery energy-stored quasi-Z-source inverter-based photovoltaic power plant with Twofold energy management system

The use of a battery energy-stored quasi-Z-source inverter (BES-qZSI) for large-scale PV power plants exhibits promising features due to the combination of qZSI and battery as energy storage system, such as single-stage power conversion (without additional DC/DC boost converter), improvements in the output waveform quality (due to the elimination of switching dead time), and continuous and smooth delivery of energy to the grid (through the battery energy storage system). This paper presents a new simplified model of a BES-qZSI to represent the converter dynamics with sufficient accuracy while using a less complex model than the detailed model (including the modelling of all switches and switching pulses). It is based on averaged values of the variables, voltage/current sources, and the same control circuit than the detailed model, except for the switching pulses generation. The simplified model enables faster time-domain simulation and is useful for control design and dynamic analysis purposes. Additionally, an energy management system has been developed to govern the power supply to grid under two possible scenarios: 1) System operator command following; or 2) economic dispatch of the stored energy. The results obtained from simulations and experimental hardware-in-the-loop (HIL) setup for different operating conditions of the grid-connected large-scale PV power plant with battery energy storage under study demonstrate the validity of the proposed simplified model to represent the dynamics of the converter and PV power plant for steady-state stability studies, long-term simulations, or large electric power systems. © 2021 The AuthorsThis work was partially supported by the Spain's Ministerio de Ciencia, Innovaci?n y Universidades (MCIU), Agencia Estatal de Investigaci?n (AEI), and Fondo Europeo de Desarrollo Regional (FEDER) Uni?n Europea (UE) (grant number RTI2018-095720-B-C32), by the Federal Center for Technological Education of Minas Gerais, Brazil (process number 23062?010087/2017-51) and by the National Council of Technological and Scientific Development (CNPq-Brazil

New and improved solutions for the configuration, management and operation of large-scale photovoltaic power plants using hybrid energy storage system

This thesis is presented in the context of multiple efforts being made by research groups in order to disseminate and evolve the technological knowledge in the renewable energy (RE) field. The motivation of this study is based on the main disadvantages of photovoltaic (PV) solar power generation compared to conventional energy sources, such as intermittency, non-dispatchability, and unreliability. From those drawbacks, the aim is to find creative solutions to mitigate these issues with a power plant combining PV and hybrid energy storage systems (HESS). In doing so, hybrid power plants represent a very interesting option for power generation and grid integration of PV systems, since they allow increased efficiency in the energy generation, as well as storing and supporting RE generation when needed.The storage systems are particularly important to deal with the intermittent nature of solar radiation. A wide variety of storage systems exists nowadays, all of them based on different operating principles and target applications. A thorough review of the literature has exposed that, depending on the application, a certain type of storage could be preferred above others. Besides, two or more different technologies working together can present complementary features. In this sense, the HESS can accomplish higher efficiencies and improved systems for grid connection. The objective is to develop new solutions to improve the configuration, management, and operation of PV plants with energy storage, designing the necessary control techniques and validating them through real-time simulations. In this context, this thesis presents a large-scale PV power plant with HESS, through a DC/DC impedance source converter (DC/DC-ZSC), and a new simplified model (SM) of the quasi Z-source inverter with battery energy storage (qZSI-BES) attached directly to the Z-network without an extra DC/DC converter. The HESS consists of battery arrays (BES) and ultracapacitors (UC). The newly designed SM is implemented, assessed, and validated experimentally in laboratory through a TYPHOON HIL system and a dSPACE MicroLabBox control board. Three different energy management strategies are implemented, using two of them advanced control techniques based on fuzzy logic. The control loops of the active, reactive, BES, and UC power have been conveniently deployed. The results obtained are coherent with the expected responses, observing an appropriate power balance and grid energy dispatch. This thesis aims for a relevant contribution in the development of low polluting energy sources that can fulfill the growing electricity demand. Following the global trends, and recognizing the importance of this knowledge for the scientific community and for society, this thesis will provide new solutions in the field of solar PV generation. In view of the fact that research has mainly focused on small-scale hybrid power plants so far, further studies are required regarding the configuration, design, control, energy management, operation, and problems associated with large PV power plants with hybrid storage

Model predictive control of a microgrid with energy-stored quasi-Z-source cascaded H-bridge multilevel inverter and PV systems

This paper presents a new energy management system (EMS) based on model predictive control (MPC) for a microgrid with solar photovoltaic (PV) power plants and a quasi-Z-source cascaded H-bridge multilevel inverter that integrates an energy storage system (ES-qZS-CHBMLI). The system comprises three modules, each with a PV power plant, quasi-impedance network, battery energy storage system (BESS), and voltage source inverter (VSI). Traditional EMS methods focus on distributing the power among the BESSs to balance their state of charge (SOC), operating in charging or discharging mode. The proposed MPC-EMS carries out a multi-objective control for an ES-qZS-CHBMLI topology, which allows an optimized BESS power distribution while meeting the system operator requirements. It prioritizes the charge of the BESS with the lowest SOC and the discharge of the BESS with the highest SOC. Thus, both modes can coexist simultaneously, while ensuring decoupled power control. The MPC-EMS proposed herein is compared with a proportional sharing algorithm based on SOC (SOC-EMS) that pursues the same objectives. The simulation results show an improvement in the control of the power delivered to the grid. The Integral Time Absolute Error, ITAE, achieved with the MPC-EMS for the active and reactive power is 20 % and 4 %, respectively, lower than that obtained with the SOC-EMS. A 1,3 % higher charge for the BESS with the lowest SOC is also registered. Furthermore, an experimental setup based on an OPAL RT-4510 unit and a dSPACE MicroLabBox prototyping unit is implemented to validate the simulation result

Emerging Converter Topologies and Control for Grid Connected Photovoltaic Systems

Continuous cost reduction of photovoltaic (PV) systems and the rise of power auctions resulted in the establishment of PV power not only as a green energy source but also as a cost-effective solution to the electricity generation market. Various commercial solutions for grid-connected PV systems are available at any power level, ranging from multi-megawatt utility-scale solar farms to sub-kilowatt residential PV installations. Compared to utility-scale systems, the feasibility of small-scale residential PV installations is still limited by existing technologies that have not yet properly address issues like operation in weak grids, opaque and partial shading, etc. New market drivers such as warranty improvement to match the PV module lifespan, operation voltage range extension for application flexibility, and embedded energy storage for load shifting have again put small-scale PV systems in the spotlight. This Special Issue collects the latest developments in the field of power electronic converter topologies, control, design, and optimization for better energy yield, power conversion efficiency, reliability, and longer lifetime of the small-scale PV systems. This Special Issue will serve as a reference and update for academics, researchers, and practicing engineers to inspire new research and developments that pave the way for next-generation PV systems for residential and small commercial applications

Control of distributed power in microgrids: PV field to the grid, islanding operation, and ultra-fast charging station.

Aquesta tesi explora el control de l'energia distribuïda en microxarxes (MG) i aborda diversos reptes relacionats amb el control, l'estabilitat, la compartició d'energia, el disseny del convertidor d'energia, la connexió a la xarxa, la càrrega ultraràpida i el subministrament d'energia renovable. El rendiment dels MG s'analitza tant en modes d'operació connectats a la xarxa com en illa, considerant diferents configuracions i escenaris de flux d'energia. La tesi se centra en diversos reptes clau, com ara maximitzar l'extracció d'energia de matrius fotovoltaiques (PV) en MG que utilitzen convertidors DC-DC, injectar potència MG excedent a la xarxa principal mitjançant inversors de font de tensió DC-AC (VSI) sota càrregues no lineals i desequilibrades, optimitzant el rendiment de MG i la compartició d'energia en mode illa mitjançant VSI, connectant-se a la xarxa principal en el punt d'acoblament comú (PCC) mitjançant transformadors de baixa freqüència (LFT) i transformadors d'estat sòlid (SST) i explorant topologies de convertidors de potència per ultra -càrrega ràpida de CC de vehicles elèctrics (EV). L'ús de SST en lloc de LFT pot millorar la capacitat de MG alhora que redueix el volum i el pes de l'arquitectura elèctrica MG. Aquesta tesi proporciona coneixements i solucions per abordar els reptes esmentats anteriorment, contribuint a l'avenç del control, l'estabilitat, la qualitat de l'energia i la integració eficient de les fonts d'energia renovables i la càrrega dels vehicles elèctrics.Esta tesis explora el control de la potencia distribuida en microrredes (MGs) y aborda diversos retos relacionados con el control, la estabilidad, el reparto de potencia, el diseño de convertidores de potencia, la conexión a la red, la carga ultrarrápida y el suministro de energías renovables. El rendimiento de las MG se analiza tanto en modo de funcionamiento conectado a la red como en modo aislado, considerando diferentes configuraciones y escenarios de flujo de potencia. La tesis se centra en varios retos clave, como la maximización de la extracción de energía de las matrices fotovoltaicas (FV) en las MG utilizando convertidores CC-CC, la inyección del excedente de energía de las MG en la red principal a través de inversores de fuente de tensión CC-CA (VSI) bajo cargas no lineales y desequilibradas, la optimización del rendimiento de las MG y del reparto de energía en modo aislado mediante VSI, la conexión a la red principal en el punto de acoplamiento común (PCC) mediante transformadores de baja frecuencia (LFT) y transformadores de estado sólido (SST), y la exploración de topologías de convertidores de potencia para la carga ultrarrápida en corriente continua de vehículos eléctricos (VE). El uso de SST en lugar de LFT puede mejorar la capacidad de la MG y, al mismo tiempo, reducir el volumen y el peso de la arquitectura eléctrica de la MG. Esta tesis aporta ideas y soluciones para abordar los retos mencionados, contribuyendo al avance del control de la MG, la estabilidad, la calidad de la energía y la integración eficiente de fuentes de energía renovables y la carga de vehículos eléctricos. Traducción realizada con la versión gratuita del traductor www.DeepL.com/TranslatorThis thesis explores the control of distributed power in microgrids (MGs) and addresses various challenges related to control, stability, power sharing, power converter design, grid connection, ultra-fast charging, and renewable energy supply. The performance of MGs is analysed in both grid-connected and islanded modes of operation, considering different configurations and power flow scenarios. The thesis focuses on several key challenges, including maximising power extraction from photovoltaic (PV) arrays in MGs utilizing DC-DC converters, injecting surplus MG power into the main grid via DC-AC voltage source inverters (VSIs) under nonlinear and unbalanced loads, optimising MG performance and power sharing in islanded mode through VSIs, connecting to the main grid at the point of common coupling (PCC) using low-frequency transformers (LFTs) and solid-state transformers (SSTs), and exploring power converter topologies for ultra-fast DC charging of electric vehicles (EVs). The use of SSTs instead of LFTs can enhance MG capability while reducing the volume and weight of the MG electrical architecture. This thesis provides insights and solutions to address the aforementioned challenges, contributing to the advancement of MG control, stability, power quality, and efficient integration of renewable energy sources and EV charging

Hybrid PV-Wind, Micro-Grid Development Using Quasi-Z-Source Inverter Modeling and Control—Experimental Investigation

This research work deals with the modeling and control of a hybrid photovoltaic (PV)-Wind micro-grid using Quasi Z-source inverter (QZsi). This inverter has major benefits as it provides better buck/boost characteristics, can regulate the phase angle output, has less harmonic contents, does not require the filter and has high power performance characteristics over the conventional inverter. A single ended primary inductance converter (SEPIC) module used as DC-DC switched power apparatus is employed for maximum power point tracking (MPPT) functions which provide high voltage gain throughout the process. Moreover, a modified power ratio variable step (MPRVS) based perturb & observe (P&O) method has been proposed, as part of the PV MPPT action, which forces the operating point close to the maximum power point (MPP). The proposed controller effectively correlates with the hybrid PV, Wind and battery system and provides integration of distributed generation (DG) with loads under varying operating conditions. The proposed standalone micro grid system is applicable specifically in rural places. The dSPACE real-time hardware platform has been employed to test the proposed micro grid system under varying wind speed, solar irradiation, load cutting and removing conditions etc. The experimental results based on a real-time digital platform, under dynamic conditions, justify the performance of a hybrid PV-Wind micro-grid with Quasi Z-Source inverter topology