Control and Supervision of Wind Energy Conversion Systems

This paper is about a PhD thesis and includes the study and analysis of the performance of an onshore wind energy conversion system. First, mathematical models of a variable speed wind turbine with pitch control are studied, followed by the study of different controller types such as integer-order controllers, fractional-order controllers, fuzzy logic controllers, adaptive controllers and predictive controllers and the study of a supervisor based on finite state machines is also studied. The controllers are included in the lower level of a hierarchical structure composed by two levels whose objective is to control the electric output power around the rated power. The supervisor included at the higher level is based on finite state machines whose objective is to analyze the operational states according to the wind speed. The studied mathematical models are integrated into computer simulations for the wind energy conversion system and the obtained numerical results allow for the performance assessment of the system connected to the electric grid. The wind energy conversion system is composed by a variable speed wind turbine, a mechanical transmission system described by a two mass drive train, a gearbox, a doubly fed induction generator rotor and by a two level converter.

Bidding and Optimization Strategies for Wind-PV Systems in Electricity Markets

The variability in non-dispatchable power generation raises important challenges to the integration of renewable energy sources into the electricity power grid. This paper provides the coordinated trading of wind and photovoltaic energy to mitigate risks due to the wind and solar power variability, electricity prices, and financial penalties arising out the generation shortfall and surplus. The problem of wind-photovoltaic coordinated trading is formulated as a linear programming problem. The goal is to obtain the optimal bidding strategy that maximizes the total profit. The wind-photovoltaic coordinated operation is modeled and compared with the uncoordinated operation. A comparison of the models and relevant conclusions are drawn from an illustrative case study of the Iberian day-ahead electricity market.

Bidding and Optimization Strategies for Wind-PV Systems in Electricity Markets Assisted by CPS

The variability in non-dispatchable power generation raises important challenges to the integration of renewable energy sources into the electricity power grid. This paper provides the coordinated trading of wind and photovoltaic energy assisted by a cyber-physical system for supporting management decisions to mitigate risks due to the wind and solar power variability, electricity prices, and financial penalties arising out the generation shortfall and surplus. The problem of wind-photovoltaic coordinated trading is formulated as a stochastic linear programming problem. The goal is to obtain the optimal bidding strategy that maximizes the total profit. The wind-photovoltaic coordinated operation is modelled and compared with the uncoordinated operation. A comparison of the models and relevant conclusions are drawn from an illustrative case study of the Iberian day-ahead electricity market.

Computer-based monitoring platform for renewable energy systems: Four experimental application cases using NI LabVIEW

Sustainability and responsible environmental behaviour constitute a vital premise in the development of the humankind. In fact, during last decades, the global energetic scenario is evolving towards a scheme with increasing relevance of Renewable Energy Sources (RES) like photovoltaic, wind, biomass and hydrogen. Furthermore, hydrogen is an energy carrier which constitutes a mean for long-term energy storage. The integration of hydrogen with local RES contributes to distributed power generation and early introduction of hydrogen economy. Intermittent nature of many of RES, for instance solar and wind sources, impose the development of a management and control strategy to overcome this drawback. This strategy is responsible of providing a reliable, stable and efficient operation of the system. To implement such strategy, a monitoring system is required.The present paper aims to contribute to experimentally validate LabVIEW as valuable tool to develop monitoring platforms in the field of RES-based facilities. To this aim, a set of real systems successfully monitored is exposed.

Offshore Wind Energy System with DC Transmission Discrete Mass: Modeling and Simulation

This paper presents an integrated model for an offshore wind energy system taking into consideration a contribution for the marine wave and wind speed with perturbations influences on the power quality of current injected into the electric grid. The paper deals with the simulation of one floating offshore wind turbine equipped with a PMSG and a two-level converter connected to an onshore electric grid. The use of discrete mass modeling is accessed in order to reveal by computing the THD on how the perturbations of the captured energy are attenuated at the electric grid injection point. Two torque actions are considered for the three-mass modeling, the aerodynamic on the flexible part and on the rigid part of the blades. Also, a torque due to the influence of marine waves in deep water is considered. PI fractional-order control supports the control strategy. A comparison between the drive train models is presented.

Blade pitch control malfunction simulation in a wind energy conversion system with MPC five-level converter

This paper is on a wind energy conversion system simulation of a transient analysis due to a blade pitch control malfunction. The aim of the transient analysis is the study of the behavior of a back-to-back multiple point clamped five-level full-power converter implemented in a wind energy conversion system equipped with a permanent magnet synchronous generator. An alternate current link connects the system to the grid. The drive train is modeled by a three-mass model in order to simulate the dynamic effect of the wind on the tower. The control strategy is based on fractional-order control. Unbalance voltages in the DC-link capacitors are lessen due to the control strategy, balancing the capacitor banks voltages by a selection of the output voltage vectors. Simulation studies are carried out to evaluate not only the system behavior, but also the quality of the energy injected into the electric grid.

Offshore Wind Energy Conversion System Connected to the Electric Grid: Modeling and Simulation

This paper is on modeling and simulation for an offshore wind system equipped with a semi-submersible floating platform, a wind turbine, a permanent magnet synchronous generator, a multiple point clamped four level or five level full-power converter, a submarine cable and a second order filter. The drive train is modeled by three mass model considering the resistant stiffness torque, structure and tower in deep water due to the moving surface elevation. The system control uses PWM by space vector modulation associated with sliding mode and proportional integral controllers. The electric energy is injected into the electric grid either by an alternated current link or by a direct current link. The model is intend to be a useful tool for unveil the behavior and performance of the offshore wind system, especially for the multiple point clamped full-power converter, under normal operation or under malfunctions.

Bidding strategy of wind-thermal energy producers

This paper presents a stochastic mixed-integer linear programming approach for solving the self-scheduling problem of a price-taker thermal and wind power producer taking part in a pool-based electricity market. Uncertainty on electricity price and wind power is considered through a set of scenarios. Thermal units are modelled by variable costs, start-up costs and technical operating constraints, such as: forbidden operating zones, ramp up/down limits and minimum up/down time limits. An efficient mixed-integer linear program is presented to develop the offering strategies of the coordinated production of thermal and wind energy generation, having as a goal the maximization of profit. A case study with data from the Iberian Electricity Market is presented and results are discussed to show the effectiveness of the proposed approach.

Determination of a Mean Solar Radiation Year and of a Typical Meteorological Year for the region of Funchal in the Madeira Island

This paper presents the determination of a mean solar radiation year and of a typical meteorological year for the region of Funchal in the Madeira Island, Portugal. The data set includes hourly mean and extreme values for air temperature, relative humidity and wind speed and hourly mean values for solar global and diffuse radiation for the period 2004-2014, with maximum data coverage of 99.7%. The determination of the mean solar radiation year consisted, in a first step, in the average of all values for each pair hour/day and, in a second step, in the application of a five days centred moving average of hourly values. The determination of the typical meteorological year was based on Finkelstein-Schafer statistics, which allows to obtain a complete year of real measurements through the selection and combination of typical months, preserving the long term averages while still allowing the analysis of short term events. The typical meteorological year validation was carried out through the comparison of the monthly averages for the typical year with the long term monthly averages. The values obtained were very close, so that the typical meteorological year can accurately represent the long term data series. The typical meteorological year can be used in the simulation of renewable energy systems, namely solar energy systems, and for predicting the energy performance of buildings.

Simulation of Malfunctions in a Wind System Powered by a DFIG

The paper is about the simulation of malfunctions in an onshore wind energy conversion system powered by a doubly fed induction generator with a two-level power converter, handling only the slip power. These malfunctions are analysed in order to be able to investigate the impact in the wind power system behaviour by comparison before, during and after the malfunctions. The malfunctions considered in the simulation includes are localized in the DC-link of the converter and in the phase change in rectifier.

Coordinated Scheduling of Wind-Thermal Gencos in Day-Ahead Markets

This paper presents a stochastic mixed-integer linear programming approach for solving the self-scheduling problem of a price-taker thermal and wind power producer taking part in a pool-based electricity market. Uncertainty on electricity price and wind power is considered through a set of scenarios. Thermal units are modeled by variable costs, start-up costs and technical operating constraints, such as: ramp up/down limits and minimum up/down time limits. An efficient mixed-integer linear program is presented to develop the offering strategies of the coordinated production of thermal and wind energy generation, aiming to maximize the expected profit. A case study with data from the Iberian Electricity Market is presented and results are discussed to show the effectiveness of the proposed approach.

Optimal Wind Bidding Strategies in Day-Ahead Markets

This paper presents a computer application for wind energy bidding in a day-ahead electricity market to better accommodate the variability of the energy source. The computer application is based in a stochastic linear mathematical programming problem. The goal is to obtain the optimal bidding strategy in order to maximize the revenue. Electricity prices and financial penalties for shortfall or surplus energy deliver are modeled. Finally, conclusions are drawn from an illustrative case study, using data from the day-ahead electricity market of the Iberian Peninsula.

Contribution to the diffuse radiation modelling in Évora, Portugal

Solar radiation data is crucial for the design of energy systems based on the solar resource. Since diffuse radiation measurements are not always available in the archive data series, either due to the inexistence of measuring equipment, shading device misplacement or missing data, models to generate these data are needed. In this work, one year of hourly and daily horizontal solar global and diffuse irradiation measurements in Évora are used to establish a new relation between the diffuse radiation and the clearness index. The proposed model includes a fitting parameter, which was adjusted through a simple optimization procedure to minimize the Least Square Error as compared to measurements. A comparison against several other fitting models presented in the literature was also carried out using the Root Mean Square Error as statistical indicator, and it was found that the present model is more accurate than the previous fitting models for the diffuse radiation data in Évora.

Perspetivas de utilização do potencial eólico em Timor-Leste

A exigência energética global está mais orientada para a utilização das fontes de Energias Renováveis (FERs), comprometendo e garantindo um desenvolvimento sustentável. Este trabalho tem como objetivo contribuir para o atingir das metas do PED 2011-2030, no que refere à utilização das FER, em particular do potencial eólico em Timor-Leste. Timor-Leste tem apresentado um grande interesse na política de aproveitamento de FER para alcançar a meta de longo prazo de PED 2030, comprometendo-se com o desenvolvimento sustentável através de ERs. Este trabalho pretende contribuir em particular com o estudo do aproveitamento de energia eólica. Com base no clima do vento de longo termo entre 2004 – 2012, da estação meteorológica (EM) de Díli e conjugando estes com os dados da campanha experimental de Martifer cedidos, de Dezembro 2008 - Novembro 2009, obteve-se o coeficiente de variabilidade (Cvariab.) inter-anual. Foi assim possível construir o mapa médio do vento de longo termo, com modelo atmosférico de mesoscala, numa resolução refinada de 3×3 km. Para a identificação dos locais mais favoráveis do vento, foi utilizado o modelo ArcGIS para georreferenciação do recurso. A filtragem das restrições e os constrangimentos do terreno permitiu construir o mapa do vento sustentável de Timor-Leste, por distritos, subdistritos, sucos, do enclave de Oecússi e a ilha de Atauro, o que conduziu à hierarquização de cinco zonas favoráveis (zona 1 - 5). A contribuição para o plano energético de Timor-Leste consiste em duas fases: - a 1ª fase o aproveitamento eólico em três PEs nas zonas monitorizadas (3 e 5) oriundo de dados cedidos pela Martifer, contabilizou-se um total de 424.694 MWh de produção de energia anual, tendo-se verificado o custo normalizado de energia (LCOE) no valor médio calculado de 0,046 €/kWh; - na 2ª fase a construção de acesso e o desenvolvimento de PEs nas zonas 1, 2 e 4 para o Cenário de Max-Renovável. Assim sendo, viabilizam a "Perspetiva de Utilização da Energia Eólica" no quadro do PED 2011 - 2030 de Timor-Leste, que viria reduzir o custo de produção de energia atual, e a emissão de CO2; Abstract: Prospects of Using Wind Energy in Timor-Leste The demand for global energy is more focused on the use of Reneweable Energy sources (REs), ensuring and committing itself to sustainable development. This study was prompted by the wish to contribute to the achievement the goals of the Strategic Development Plan (PED 2011-2030) regarding the use of REs, particularly the wind energy in Timor-Leste. Timor-Leste has presented a great interest in the use of renewable energy sources policy to achieve the long term goal of the PED 2030, committing to a sustainable development through renewable energy. This thesis intends to contribute in particular with the study of the use of wind energy. Based on the long term wind climate between 2004 and 2012 of the Díli weather station and combining these data with the Martifer campaign experimental data of December 2008 - November 2009, the interannual variation coefficient (Cv) was obtained. Thus, it was possible to build the map of long term average wind with atmospheric mesoscale model in a refined resolution of 3×3 km. The ArcGIS model was used for the identification of the most favorable locations of the wind for its georeferencing. The constraining of filtering and the constraints of the terrain allowed to construe the sustainable wind map of Timor-Leste in distritos, subdistritos, sucos, and also of the enclave of Oecussi and Atauro island, which led to the ranking of five favorable areas (zone 1-5) for an immediate experimental campaign of wind characterization and utilization of this resource in wind parks. The contribution to Timor-Leste's energy plan consists of two phases: - the first phase of three wind farms in zone (3 and 5) from data provided by Martifer, a total of 424,694 MWh, and levelyzed cost of electricity (LCOE) in the calculated average value of 0.046 €/kWh; - in the second phase the construction of access and development of wind farms in zones 1, 2 and 4 for the Max-Renewable Scenario. As such, they make possible the "Perspective of Wind Energy Use" in Timor Leste’s PED 2011 - 2030, which would reduce current energy production costs and CO2 emissions.

Armazenamento sazonal de energia solar térmica de baixa temperatura para climatização de edifícios

Face aos padrões atuais de vida, em que despendemos a maior parte do nosso tempo no interior de edifícios, com um nível de conforto que ninguém quer abdicar, urge o desenvolvimento de tecnologias de climatização sustentáveis. Devido a uma combinação única de fatores, casas de baixo consumo de energia (e também casas passivas) em Portugal, são particularmente adequadas de explorar as vantagens da energia solar térmica, especialmente quando combinado com armazenamento sazonal de energia. No entanto nenhum exemplo documentado existe de como esta sinergia pode ser explorada com sucesso em Portugal, ilustrando assim o modo em que a necessidade de aquecimento pode ser colmatada de uma forma sustentável sem o uso de combustíveis fósseis. A energia solar é uma excelente alternativa de fonte de energia para aquecimento de edifícios. Um principal fator que limita a sua aplicação é que é uma fonte de energia com uma disponibilidade média de variação cíclica. O uso de armazenamento sazonal de energia pode reduzir substancialmente o custo do sistema solar que é capaz de fornecer até 100% das necessidades energéticas dos edifícios. Estes sistemas são projetados para armazenar a energia solar durante o verão e reter o calor armazenado para posterior utilização durante o inverno; Abstract: SEASONAL SOLAR THERMAL ENERGY STORAGE FOR LOW TEMPERATURE HEATING BUILDINGS. Given the current standards of living, where we spent most of our time inside buildings, with a level of Comfort that no one wants to give up, urges the development of sustainable climate control technologies. Due to a unique combination of factors, low energy (and also passive) houses in Portugal are particularly well suited to exploiting the advantages of solar thermal energy especially when combined with seasonal energy storage. However no documented example there of how this synergy can be exploited successfully in Portugal, illustrating the way in which the need for heating can be addressed in a sustainable manner without the use of fossil fuels. Solar energy is an important alternative energy source for heating applications. One main factor that limits its application is that it is an energy source with an average availability of cyclical variation. The use of seasonal thermal energy storage can substantially reduce the cost of solar energy systems that can supply up to 100% of buildings energy needs. Such systems are designed to collect solar energy during the summer and retain the stored heat for use during the winter.