Este trabalho apresenta a avaliação dos impactos elétricos da inserção da geração distribuída de sistemas fotovoltaicos conectados à rede de distribuição em baixa tensão, com a finalidade de identificar os impactos e demonstrar que estes podem ser controlados. O estudo consistiu de uma avaliação teórica e de um estudo de caso da inserção da geração fotovoltaica considerando aspectos da qualidade de energia da rede, curva de carga resultante, vida útil de transformadores e gestão ativa da demanda. Os resultados mostraram que a inserção da geração fotovoltaica na rede de baixa tensão altera a curva de carga da unidade consumidora, mas que essas alterações podem ser controladas pela gestão ativa da demanda utilizando armazenamento de energia. Os resultados também mostraram que a geração fotovoltaica também afeta a tensão e o fator de potência da unidade consumidora, mas que essas alterações podem ser controladas pela produção de potência reativa pelo inversor. Além disso, verificou- se que a geração fotovoltaica não afetou a distorção harmônica de tensão da rede e que aumentou a vida útil do transformador. / This work presents the evaluation of grid connected photovoltaic systems\' impact on low voltage electrical grid, in order to identify the impacts and demonstrate that it can be controlled. The study consisted of a theoretical evaluation and of a case study of photovoltaic generation inclusion considering aspects of grid power quality, resulting load curve, lifespan of transformers and demand side management. The results showed that the inclusion of photovoltaic generation in low voltage network changes the load curve of the consumer unit, but these changes can be controlled by demand side management using energy storage. The results also showed that the photovoltaic generation also affects the voltage and the power factor of the consumer unit, but these changes can be controlled by the production of reactive power by the inverter. Furthermore, it was found that the photovoltaic generation does not affect the voltage harmonic distortion of the mains and it increases the lifespan of the transformer.

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2015-10-26T16:05:56Z No. of bitstreams: 1 Gabriela Schenkel_.pdf: 3048283 bytes, checksum: cd479115e88afd207554abd627ee1c17 (MD5) / Made available in DSpace on 2015-10-26T16:05:56Z (GMT). No. of bitstreams: 1 Gabriela Schenkel_.pdf: 3048283 bytes, checksum: cd479115e88afd207554abd627ee1c17 (MD5) Previous issue date: 2015-02 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os sistemas fotovoltaicos conectados à rede tem como finalidade a conversão da energia solar em energia elétrica. No Brasil, recentemente foi dado o primeiro passo efetivo com a publicação pela ANEEL da Resolução Normativa n° 482. Esta resolução, publicada em 17 de abril de 2012, possibilita à um consumidor doméstico e comercial possuir um sistema de microgeração de energia (hidráulica, solar, eólica, biomassa ou cogeração qualificada) conectado à rede elétrica e fazer compensação de energia. Neste trabalho foi instalado em caráter experimental, no Laboratório de Energias Renováveis da Unisinos, um sistema fotovoltaico conectado à rede com uso de um modelo de microinversor, e buscou-se por meio desta instalação e do monitoramento, analisar o comportamento elétrico e energético do sistema. O sistema é composto por um módulo monocristalino LG255S1C de 255 Wp conectado a um microinversor ENPHASE M215 de 215 W. O período de monitoramento foi de 1° de agosto até 20 de dezembro de 2014. Uma central de aquisição de dados Agilent HP 34970A foi empregada para coletar dados de irradiância no plano do gerador fotovoltaico, corrente e tensão na entrada e saída do microinversor, temperatura de uma célula FV no centro do módulo fotovoltaico e temperatura no dissipador do microinversor. Também foi utilizado como medidor o analisador de energia Fluke 43B, que coleta os dados de potência ativa, potência reativa e potência aparente injetada na rede elétrica pelo sistema. Índices de qualidade de energia como a distorção harmônica total de corrente e fator de deslocamento também foram medidos. A eficiência média diária máxima, considerando a incerteza, medida no microinversor empregado foi de 95,18 % e é semelhante aos valores de eficiência média diária dos microinversores de primeira e segunda geração. O sistema fotovoltaico monitorado com o uso do microinversor atingiu o valor máximo de desempenho global de 0,93. A produção de energia máxima diária em corrente alternada foi de 1,49 kWh. Estima-se, levando em consideração este valor, que a produção mensal pode ser de até 44,7 kWh. Isto significa uma redução de 58 % no consumo de energia em uma residência, levando em consideração o custo de disponibilidade e o sistema instalado em uma residência com consumo médio mensal da região nordeste que é de 120 kWh. / Photovoltaic grid-connected systems aims the conversion of solar energy into electrical energy. In Brazil, was recently given the first effective step with the publication by ANEEL Normative Resolution No. 482. This resolution published on 17 th April, 2012, enables domestic and commercial consumers have an energy microgeneration system (hydro, solar, wind, biomass or qualified cogeneration) connected to mains power and make compensation. In this work was mounted on an experimental character, in the Renewable Energy Laboratory of Unisinos, a photovoltaic grid-connected system that uses a microinverter model, and through this installation and monitoring, analyse the electrical and energetical behavior of the system. The system consists of a 255 Wp LG255S1C monocrystalline module, connected to a 215 W ENPHASE M215 microinverter. The monitoring period was 1 st August to 20 th December, 2014. A central acquisition of Agilent HP 34970A data was used to collect data irradiance in the plane of the PV array, current and voltage at the input and output of microinverter, temperature of a PV cell in the center of the PV module and the microinverter sink. It was also used as a measuring the energy analyzer Fluke 43B, which collects the data of active power, reactive power and apparent power injected into the grid by the system. Power quality indices as the total harmonic current distortion and displacement factor were also measured. The maximum daily average efficiency, considering the uncertainty, measured on the employed microinverter was 95.18 % and is similar than the daily average efficiency values of microinverters of first and second generation. The photovoltaic system monitored using the microinverter peaked overall performance of 0.93. The production maximum daily energy into alternating current was 1.49 kWh. It is estimated taking into account the value that the monthly production can achieved 44.7 kWh. This means a reduction of 58 % in the consumption of a residence considering the availability cost and that the system is installed in a residence with the northest comsumption whose the average monthly consumption is 120.00 kWh.

Este trabalho propõe um procedimento para qualificar sistemas fotovoltaicos conectados à rede, o qual possui dois focos principais: o comissionamento e a caracterização da produção de energia. Também resume alguns aspectos normativos relacionados aos sistemas fotovoltaicos, apresenta os principais parâmetros de desempenho utilizados para caracterizar um sistema fotovoltaico, propõe uma metodologia para calcular a energia injetada na rede, a qual incorpora modelos matemáticos e procedimentos de medição, tanto novos quanto convencionais, e aplica essa metodologia em um estudo de caso de um sistema fotovoltaico real. / This work proposes a procedure for qualifying grid-connected photovoltaic systems, which has two main focuses: the commissioning and the characterization of energy production. The work also summarizes some regulatory aspects related to photovoltaic systems, presents the main parameters used to characterize the performance of a photovoltaic system, proposes a methodology to calculate the energy injected into the grid, which incorporates both new and conventional mathematical models and measurement procedures, and applies this methodology to a case of study of a real photovoltaic system.

Doctor of Philosophy / Department of Electrical and Computer Engineering / Behrooz Mirafzal / Voltage source inverters (VSIs) are an essential interface for grid integration of renewable energy resources. Grid-tied VSIs are employed in power grids to integrate distributed generation units, e.g. photovoltaic arrays, wind turbines and energy storage units, to the utility and extract the maximum energy from the DG units in an efficient manner. However, the stability of VSIs and by extension the entire DG system can be degraded under abnormal grid conditions. In this dissertation, new control and switching techniques for stability and power quality improvement of grid-tied VSIs under abnormal grid conditions are presented. For grids with a low inertia and a low short-circuit ratio, commonly referred to as weak grids, grid connection may make VSIs susceptible to voltage distortion and instability. In this dissertation, through root locus analysis of a detailed state-space model, the design of several circuit and control parameters of the grid-tied VSI are evaluated for improving stability in weak grids. It is shown that grid-side filter inductances can be increased for stable operation of VSIs in weak grids. Accordingly, a virtual inductance emulating the effect of an increased inductance in the grid-side filter is developed in this dissertation, which enables stable operation of VSIs in weak grids without the tradeoffs, i.e. additional voltage drop, increased cost and larger size, associated with a larger inductor. The virtual inductance scheme is realized through the injection of a feedforward current element in the VSI controller through a gain component. The measured grid currents, which are sensed for regular VSI controller operation, are employed as the feedforward component eliminating the need for any additional sensors for the utilization of this control scheme. Furthermore, a direct model reference adaptive control (MRAC) scheme is employed in this dissertation to tune the virtual inductance gain block according to a stable reference model for varying grid conditions. The use of direct MRAC scheme allows tuning of the virtual inductance block without the need for a plant parameter estimation stage. The virtual inductance scheme enables stable operation of VSIs in weak grids without system parameter redesign, thereby maintaining the steady-state performance of the system. The efficacy of the virtual inductance feedforward scheme is verified through hardware tests carried out on a three-phase grid-tied experimental setup. Along with extracting energy from the DG sources, grid-tied VSIs are capable of providing various ancillary services to the utility under abnormal conditions. However, providing ancillary services could drive the inverter voltages beyond the linear modulation region resulting in grid current distortions, which could violate the requirements for grid integration of DGs. An atypical pulse width modulation (PWM) technique is proposed in this dissertation, which maximizes the dc-bus utilization of VSIs, which in turn enables the VSIs to supply the maximum extracted power from the DG units to the grid when providing ancillary services while operating in the linear modulation region. The switching scheme is realized by injecting common mode components in the PWM references, computed based on instantaneous reference magnitudes. The proposed scheme is suitable when providing both symmetrical and asymmetrical ancillary services. In this dissertation, negative-sequence compensation and harmonic compensation are employed as instances of symmetrical and asymmetrical ancillary services. The proposed scheme can be integrated with any control scheme and carrier-based PWM combinations. The efficacy of the proposed atypical PWM scheme is verified through both simulation and hardware tests.

A plug-in hybrid electric vehicle (PHEV) is a vehicle powered by a combination of an internal combustion engine and an electric motor with a battery pack. The battery pack can be charged by plugging the vehicle into the electric grid or from using excess engine power. A PHEV allows for all electric operation for limited distances, while having the operation and range of a conventional hybrid electric vehicle on longer trips. A PHEV design with design parameters electric motor size, engine size, battery capacity, and battery chemistry type, is optimized with minimum cost as a figure of merit. The PHEV is required to meet a fixed set of performance constraints consisting of 0-60 mph acceleration, 50-70 mph acceleration, 0-30 mph acceleration in all electric operation, top speed, grade ability, and all electric range. The optimization is carried out for values of all electric range of 10, 20, and 40 miles. The social and economic impacts of the optimum designs in terms of reduced gasoline consumption and carbon emissions reduction are calculated. Argonne National Laboratorys Powertrain Systems Analysis Toolkit is used to simulate the performance and fuel economy of the PHEV designs. The costs of different PHEV components and the present value of battery replacements over the vehicles life are used to determine the designs drivetrain cost. The resulting optimum PHEVs are designs using lead acid battery type. The optimum design parameter values are all determined by a single controlling performance constraint. The PHEV designs show a 63% to 80% reduction in gasoline consumption and a 53% to 47% reduction in CO2 emissions. The PHEV designs have an annual gas savings of $696 to $643 per year over the average sedan meeting the 27.5 mpg CAFE standards.

In this dissertation, a high-frequency (HF) transformer isolated grid-connected power converter system with battery backup function is proposed for a small-scale wind generation system (less than 100 kW) using permanent magnet synchronous generator (PMSG). The system includes a main HF isolated DC/AC grid-connected converter and a bidirectional HF isolated DC/DC converter. Through literature survey and some comparative studies, a HF isolated DC/DC converter followed by a line connected inverter (LCI) is chosen as the grid-connected scheme. After reviewing several topologies which were used in such a DC/AC converter with an unfolding stage, a DC/AC grid-connected converter based on dual- bridge LCL-type resonant topology is proposed. Through the control of the phase- shift angle between the two bridges, a rectified sinusoidal dc link current can be modulated, which in turn can be unfolded by the LCI. This converter is analyzed with Fourier series analysis approach. It is shown that all switches in both bridges can work in zero-voltage switching (ZVS) at any phase-shift and load conditions. The redundancy of the dual-bridge structure make it easy to accommodate higher power flow. A design example of a 500 W converter is given and simulated. A prototype is built and tested in the lab to validate its performance. The simulation and experimental results show a reasonable match to the theoretical analysis. The expansion to three-phase grid-connection is discussed with phase-shifted parallel operation of three identical units. Input and output current harmonics of different arrangements are analyzed to search for the best choice. As the feature of a hybrid wind generation application, the battery backup function is fulfilled with a bidirectional HF transformer isolated DC/DC converter. This dual-bridge series resonant converter (DBSRC) is analyzed with two ac equivalent circuit approaches for resistive load and battery load respectively, which give same results. Soft-switching is achieved for all switches on both sides of the HF transformer. Test plots obtained from simulation and experiment are included for validation.

Este trabalho apresenta a avaliação dos impactos elétricos da inserção da geração distribuída de sistemas fotovoltaicos conectados à rede de distribuição em baixa tensão, com a finalidade de identificar os impactos e demonstrar que estes podem ser controlados. O estudo consistiu de uma avaliação teórica e de um estudo de caso da inserção da geração fotovoltaica considerando aspectos da qualidade de energia da rede, curva de carga resultante, vida útil de transformadores e gestão ativa da demanda. Os resultados mostraram que a inserção da geração fotovoltaica na rede de baixa tensão altera a curva de carga da unidade consumidora, mas que essas alterações podem ser controladas pela gestão ativa da demanda utilizando armazenamento de energia. Os resultados também mostraram que a geração fotovoltaica também afeta a tensão e o fator de potência da unidade consumidora, mas que essas alterações podem ser controladas pela produção de potência reativa pelo inversor. Além disso, verificou- se que a geração fotovoltaica não afetou a distorção harmônica de tensão da rede e que aumentou a vida útil do transformador. / This work presents the evaluation of grid connected photovoltaic systems\' impact on low voltage electrical grid, in order to identify the impacts and demonstrate that it can be controlled. The study consisted of a theoretical evaluation and of a case study of photovoltaic generation inclusion considering aspects of grid power quality, resulting load curve, lifespan of transformers and demand side management. The results showed that the inclusion of photovoltaic generation in low voltage network changes the load curve of the consumer unit, but these changes can be controlled by demand side management using energy storage. The results also showed that the photovoltaic generation also affects the voltage and the power factor of the consumer unit, but these changes can be controlled by the production of reactive power by the inverter. Furthermore, it was found that the photovoltaic generation does not affect the voltage harmonic distortion of the mains and it increases the lifespan of the transformer.

Neste tabalho à realizado o estudo de um conversor de trÃs nÃveis com ponto neutro grampeado (NPC), proposto para a interligaÃÃo de sistemas de conversÃo de energia à rede elÃtrica. Para tanto à utilizado um filtro indutivo L, tÃcnicas de controle vetorial, e a tÃcnica PLLcomo mÃtodo de sincronismo. SÃo desenvolvidas equaÃÃes para a determinaÃÃo das perdas do conversor, as quais podem ser aplicadas a diversas tÃcnicas de modulaÃÃo PWM. TrÃs tÃcnicas sÃo apresentadas: modulaÃÃo PD; modulaÃÃo com injeÃÃo de terceiro harmÃnico (THIPWM); e modulaÃÃo vetorial baseada em portadora (CB-SVPWM). Toda a modelagem do sistema à apresentada, bem como um exemplo de projeto para um sistema de 6 kW.SÃo realizadas simulaÃÃes computacionaispara diferentes estudos de caso, validando o projeto do conversor e a modelagem desenvolvida. A resposta Ãs dinÃmicas do sistema à satisfatÃria, sendo o conversor capaz de controlar o fluxo de potÃncia ativa (com fator de potÃncia uniÃrio) e reativa entregues à rede. / This work deals with the study of a three-level inverter with Neutral Point Clamped (NPC), proposed for the interconnection of energy conversion systems to the grid. In order to accomplish a complete study, an inductive filter L is proposed, as well as vector control techniques and a PLL synchronization method. Equations are developed for the determination of the losses of the converter, which can be applied to various PWM techniques. Three Modulation techniques are presented: Phase Disposition modulation(PD), modulation with injection of the third harmonic (THIPWM) and carrier-based space vector modulation (SVPWM-CB). The complete modeling system is presented, as well as an example for designing a system of 6 kW. Numerical simulations are performed for different study cases, validating the converter design and modeling developed. The simulation results show that the proposed NPC converter is fully satisfactory, the converter being able to control the active (unity power factor) and reactive power flow delivered to the grid.

Thesis (PhD (Electrical Engineering))--Cape Peninsula University of Technology, 2019 / Energy systems based on fossil fuel have demonstrated their abilities to permit economic development. However, with the fast exhaustion of this energy source, the expansion of the world energy demand and concerns over global warming, new energy systems dependent on renewable and other sustainable energy are gaining more interests. It is a fact that future development in the energy sector is founded on the utilisation of renewable and sustainable energy sources. These energy sources can enable the world to meet the double targets of diminishing greenhouse gas emissions and ensuring reliable and cost-effective energy supply. Fuel cells are one of the advanced clean energy technologies to substitute power generation systems based on fossil fuel. They are viewed as reliable and efficient technologies to operate either tied or non-tied to the grid to power applications ranging from domestic, commercial to industrial. Multiple fuel cell stacks can be associated in series and parallel to obtain a fuel cell system with high power up to megawatts. The connection of megawatts fuel cell systems to a utility grid requires that the power condition unit serving as the interface between the fuel cell plant and the grid operates accordingly. Different power conditioning unit topologies can be adopted, this study considers a multilevel inverter. Multilevel inverters are getting more popularity and attractiveness as compared to conventional inverters in high voltage and high-power applications. These inverters are suitable for harmonic mitigation in high-power applications whereby switching devices are unable to function at high switching frequencies. For a given application, the choice of appropriate multilevel topology and its control scheme are not defined and depend on various engineering compromises, however, the most developed multilevel inverter topologies include the Diode Clamped, the Flying Capacitor and the Cascade Full Bridge inverters. On the other hand, a multilevel inverter can be either a three or a five, or a nine level, however, this research focuses on the three-level diode clamped inverters. The aim of this thesis is to model and control a three-level diode clamped inverter for the grid connection of a megawatt fuel cell stack. Besides the grid, the system consists of a 1.54 MW operating at 1400 V DC proton exchange membrane fuel cell stack, a 1.26 MW three-level diode clamped inverter with a nominal voltage of 600 V and an LCL filter which is designed to reduce harmonics and meet the standards such as IEEE 519 and IEC 61000-3-6. The inverter control scheme comprises voltage and current regulators to provide a good power factor and satisfy synchronisation requirements with the grid. The frequency and phase are synchronised with those of the grid through a phase locked loop. The modelling and simulation are performed using Matlab/Simulink. The results show good performance of the developed system with a low total harmonic distortion of about 0.35% for the voltage and 0.19% for the current.

Thesis (MEng (Electrical Engineering))--Cape Peninsula University of Technology, 2019 / Electric utilities are confronted with challenges like rising fuel costs, aging equipment, increasing energy demand, frequency regulation and the difficulty to integrate renewable energy resources into the grid. The presence of photovoltaic (PV) penetration on the utility grid is also increasing significantly in recent years. With the recent rise in PV penetration and the advancement of the global PV industry, there is an urgent and a necessary need to introduce features in PV systems that will make them respond smartly. However, much of these can be addressed without negatively affecting the total performance and power quality of the grid. Hence, engaging smart Grid technologies, and leveraging the benefits of the distributed nature of PV, new prospects to unearth value can be created. Through the implementation of progressive energy storage techniques, efficient two-way communications, a grid-tied PV system can create significant value, mostly through improved PV contribution in grid support functions like frequency regulation. An enhanced frequency regulation functioning scheme for a grid-connected photovoltaic (PV) system is modelled in MATLAB/Simulink software environment. The system is designed to operate in grid ancillary services precisely, frequency regulation function. The model consists of a Photovoltaic (PV) plant with a battery connected to the grid through a three-phase inverter. A bi-directional DC-DC converter between the grid and the battery system is included. The model has a battery storage system that provide steady and regular active/reactive powers available while the grid transmit specific amounts of power needed for a specific duration. According to the design, either the grid or the PV system depending on the dominant energy situation charges the battery. The battery is designed to discharge only when the grid demands energy from the PV and if the PV system fails to meet the demanded active power or reactive power. The PV system and the battery storage is integrated with the grid with the aid of dc-ac inverter in such a manner that bi-directional flow of active and reactive power is achieved. A 1 MW PV system is connected to the utility grid through a three-phase voltage source inverter system. The grid nominal frequency is set at 50 Hz under normal operation. However, the frequency decreased when the PV was not producing required power hence, the battery responded almost instantaneously and returned the frequency to the nominal frequency. The effectiveness of battery storage system for utility grid frequency regulation was substantiated from the simulation results attained.