DC-DC converter based photovoltaic simulator with a double current mode controller

This thesis presents the performance of a DC-DC converter based with current mode controller photovoltaic (PV) simulator which emulates the output characteristics of a real PV module. A portable PV simulator prototype of 85 W is examined in terms of its steady state IV curve matching capacity and the convergence time corresponding to step change in current source load, voltage source load, and insolation levels. The current-voltage (IV) characteristics of the PV module are implemented as a look-up-table (LUT) which determines the reference output current from measured output voltage. A Thevenin Equivalent Method approach to PV arrays analysis is also included in order to model the small-signal linearized characteristics. Extensive simulation results obtained in MATLAB are included to show that the PV simulator can work in most situations as a real PV module. Experimental results verify performance with current source and voltage source loads --Abstract, page iii

Standalone Photovoltaic Power Stabilizer Using Double Series Connected Converter in Sudden Cloud Condition

Renewable energy is clean energy that cannot harm the environment in its way, especially on standalone photovoltaic electricity generation. The only problem with renewable energy electricity generation is the intermittency and its instability in power quality and power efficiency. Power system stability in renewable energy is essential during the real environmental case problem such as the sudden cloud. The sudden cloud, known for its ability to decrease solar irradiance input, depends on how thick and big the cloud is. Several attempts had been tried to increase renewable energy power system stability, including modifying its maximum power point tracker with a new algorithm such as perturb and observe. This paper discussed an improved way of maintaining renewable energy power system stability using perturb and observe Algorithm in a double series-connected Converter as the current and power stabilizer. The results show that the current overshoot has decreased by 65,336%, and the current sudden cloud undershoot decreased by 10,529%. Power overshoot also decreased by 43,685%, and the power of sudden cloud undershoot has decreased by 7,133%

Standalone Photovoltaic Power Stabilizer Using Double Series Connected Converter in Sudden Cloud Condition

Renewable energy is clean energy that cannot harm the environment in its way, especially on standalone photovoltaic electricity generation. The only problem with renewable energy electricity generation is the intermittency and its instability in power quality and power efficiency. Power system stability in renewable energy is essential during the real environmental case problem such as the sudden cloud. The sudden cloud, known for its ability to decrease solar irradiance input, depends on how thick and big the cloud is. Several attempts had been tried to increase renewable energy power system stability, including modifying its maximum power point tracker with a new algorithm such as perturb and observe. This paper discussed an improved way of maintaining renewable energy power system stability using perturb and observe Algorithm in a double series-connected Converter as the current and power stabilizer. The results show that the current overshoot has decreased by 65,336%, and the current sudden cloud undershoot decreased by 10,529%. Power overshoot also decreased by 43,685%, and the power of sudden cloud undershoot has decreased by 7,133%

Optimal sizing of hybrid renewable energy systems for rural electrification

Includes bibliograhical references.This project has the objective of creating a tool for feasibility assessment and recommendations of sizing of hybrid renewable energy systems in rural areas in South Africa. This involves the development of a tool which would analyse information input about the climate of the area and the load demand

Modeling, Analysis, and Design of a PV-Based Grid-Tied Plug-In Hybrid Electric Vehicle Battery Pack Charger

Ever-increasing fossil fuels consumption in recent decades has emitted tremendous amounts of greenhouse gases, a big part of which cannot be absorbed by natural processes happening in nature. These gases have increased earth temperature by absorbing extra radiations from sunlight and turning them into heat. Global warming has had terrible effects for all creatures around the world and can threat life on Earth in future. Utilization of green or renewable energies during the recent years is getting more popular and can be a solution to this serious problem. A big source of these pollutants is transportation sector. Electrification of transportation can noticeably reduce greenhouse gasses if the electricity is obtained using renewable energy sources. Otherwise, it will just shift the problem from streets to fossil fuel power plants. Electric vehicles (EVs) were introduced around one century ago; however, they were replaced by internal combustion engine cars over time. Nevertheless, recently they are getting more interest because of their superior performance and clean operation. Solar electricity which can be obtained using photovoltaic panels is one of the easiest ways as long as sun is available. They can be easily mounted on the roofs of buildings or roof tops of parking slots generating electric power to charge the battery pack of the EVs while providing shade for the cars. Since solar energy is intermittent and variable, power grid should be involved to ensure enough power is available. Conventional solar chargers inject power to the grid and use grid as the main source because of its reliability and being infinite. Hence, they use grid as a kind of energy storage system. This approach can lead to problems for grid stability if solar panels are utilized in large scales and comparable to the grid. In this work, a solar powered grid-tied EV/PHEV charger is introduced which uses all the available power from PV panels as the main energy source and drains only the remaining required power from the grid. The proposed configuration provides great flexibility and supports all the possible power flows. To design an efficient system the load should be known well enough first. A comprehensive study has been done about behavior, characteristics and different models of different chemistries of batteries. Specific phenomena happening in battery packs are outlined. A novel maximum power point tracking (MPPT) technique has been proposed specifically for battery charging applications. A specific configuration involving DC link coupling technique has been proposed to connect different parts of the system. Different possible topologies for different parts of the proposed configuration have been considered and the suitable ones have been selected. Dual active bridge topology is the heart of this configuration which acts as the bidirectional charger. A detailed state space modeling process has been followed for the power converters and various small signal transfer functions have been derived. Controllers have been designed for different power converters using SISO design tool of Matlab/Simulink. Different modes of operation for the charger including constant current mode (CCM) and constant voltage mode (CVM) have been analyzed and appropriate cascade controllers have been designed based on required time domain and frequency domain characteristics. Finally, simulation tests have been conducted and test results have been graphed and analyzed for different modes of operation, all possible power flows and various voltage and current set points

Design and simulation of converters operating in a renewable energy based smart grid

En el treball de fi de màster “Disseny i simulació d'un convertidor que funciona en una xarxa intel·ligent basada en energies renovables” s'aborda el disseny i la simulació d'un convertidor per a la seva integració en una xarxa intel·ligent basada en energies renovables. L'objectiu principal d'aquest projecte és investigar i desenvolupar dos sistemes proposats: en primer lloc, la integració d'una planta fotovoltaica en la xarxa elèctrica; i, en segon lloc, la integració d'una planta fotovoltaica juntament amb un sistema d'emmagatzematge d'energia i una càrrega de corrent altern connectat mitjançant un inversor. L'estudi se centra en la recerca i la recopilació d'informació sobre les xarxes intel·ligents basades en energies renovables, explorant els conceptes i tecnologies clau necessaris per a la integració reeixida de fonts d'energia renovable en les xarxes elèctriques. A més, es durà a terme una anàlisi exhaustiva sobre l'emmagatzematge d'energia, investigant les diferents tecnologies i sistemes d'emmagatzematge disponibles. Així mateix, s'investiga el disseny i el control de convertidors utilitzats en la formació de xarxes, analitzant els principis de funcionament i els algorismes de control necessaris per a regular la tensió i la freqüència de la xarxa. Es duu a terme una anàlisi detallada del sistema proposat, estudiant la seva configuració, els components involucrats i la seva interconnexió amb la xarxa elèctrica existent. A partir d'aquesta anàlisi, es realitza el disseny i desenvolupament dels convertidors necessaris per al sistema de generació i emmagatzematge d'energia. Es dimensionen adequadament els convertidors i es dissenyen els algorismes de control necessaris per a garantir el funcionament òptim del sistema. Per a avaluar i analitzar el rendiment del sistema proposat, s'utilitza el paquet de programari MATLAB/Simulink per al modelatge i la simulació. Això permet realitzar proves en diferents condicions i ajustar els paràmetres de disseny i control dels convertidors per a aconseguir un acompliment òptim del sistema. Els resultats obtinguts en les simulacions són validats mitjançant comparacions amb dades reals o resultats experimentals, assegurant l'eficàcia i fiabilitat del disseny proposat. Aquest treball es documenta en un informe complet i analític, que inclou una explicació detallada dels fonaments teòrics, la descripció dels passos de disseny i simulació, la presentació dels resultats obtinguts i una anàlisi crítica d'aquestsEn el trabajo de fin de máster “Diseño y simulación de un convertidor que funciona en una red inteligente basada en energías renovables” se aborda el diseño y la simulación de un convertidor para su integración en una red inteligente basada en energías renovables. El objetivo principal de este proyecto es investigar y desarrollar dos sistemas propuestos: en primer lugar, la integración de una planta fotovoltaica en la red eléctrica; y, en segundo lugar, la integración de una planta fotovoltaica junto con un sistema de almacenamiento de energía y una carga de corriente alterna conectada mediante un inversor. El estudio se centra en la investigación y la recopilación de información sobre las redes inteligentes basadas en energías renovables, explorando los conceptos y tecnologías clave necesarios para la integración exitosa de fuentes de energía renovable en las redes eléctricas. Además, se llevará a cabo un análisis exhaustivo sobre el almacenamiento de energía, investigando las diferentes tecnologías y sistemas de almacenamiento disponibles. Asimismo, se investiga el diseño y el control de convertidores utilizados en la formación de redes, analizando los principios de funcionamiento y los algoritmos de control necesarios para regular la tensión y la frecuencia de la red. Se lleva a cabo un análisis detallado del sistema propuesto, estudiando su configuración, los componentes involucrados y su interconexión con la red eléctrica existente. A partir de este análisis, se realiza el diseño y desarrollo de los convertidores necesarios para el sistema de generación y almacenamiento de energía. Se dimensionan adecuadamente los convertidores y se diseñan los algoritmos de control necesarios para garantizar el funcionamiento óptimo del sistema. Para evaluar y analizar el rendimiento del sistema propuesto, se utiliza el paquete de software MATLAB/Simulink para el modelado y la simulación. Esto permite realizar pruebas en diferentes condiciones y ajustar los parámetros de diseño y control de los convertidores para lograr un desempeño óptimo del sistema. Los resultados obtenidos en las simulaciones son validados mediante comparaciones con datos reales o resultados experimentales, asegurando la eficacia y fiabilidad del diseño propuesto. Este trabajo se documenta en un informe completo y analítico, que incluye una explicación detallada de los fundamentos teóricos, la descripción de los pasos de diseño y simulación, la presentación de los resultados obtenidos y un análisis crítico de los mismosThe Master's thesis "Design and simulation of a converter operating in a smart grid based on renewable energies" deals with the design and simulation of a converter for its integration in a smart grid based on renewable energies. The main objective of this project is to investigate and develop two proposed systems: firstly, the integration of a photovoltaic plant into the power grid; and secondly, the integration of a photovoltaic plant together with an energy storage system and an AC load connected by an inverter. The study focuses on research and information gathering on smart grids based on renewable energy, exploring the key concepts and technologies required for the successful integration of renewable energy sources into power grids. In addition, a comprehensive analysis of energy storage will be carried out, investigating the different storage technologies and systems available. The design and control of converters used in grid formation is also investigated, analyzing the operating principles and control algorithms required to regulate the voltage and frequency of the grid. A detailed analysis of the proposed system is carried out, studying its configuration, the components involved and its interconnection with the existing electrical network. Based on this analysis, the design and development of the converters required for the energy generation and storage system is carried out. The converters are adequately sized and the necessary control algorithms are designed to guarantee the optimal operation of the system. To evaluate and analyze the performance of the proposed system, the MATLAB/Simulink software package is used for modeling and simulation. This allows testing under different conditions and adjusting the design and control parameters of the converters to achieve optimal system performance. The results obtained in the simulations are validated by comparisons with real data or experimental results, ensuring the effectiveness and reliability of the proposed design. This work is documented in a comprehensive and analytical report, which includes a detailed explanation of the theoretical background, description of the design and simulation steps, presentation of the results obtained and a critical analysis of the result

Voltage Management Of Distribution Networks With High Penetration Of Distributed Photovoltaic Generation Sources

Installation of photovoltaic (PV) units could lead to great challenges to the existing electrical systems. Issues such as voltage rise, protection coordination, islanding detection, harmonics, increased or changed short-circuit levels, etc., need to be carefully addressed before we can see a wide adoption of this environmentally friendly technology. Voltage rise or overvoltage issues are of particular importance to be addressed for deploying more PV systems to distribution networks. This dissertation proposes a comprehensive solution to deal with the voltage violations in distribution networks, from controlling PV power outputs and electricity consumption of smart appliances in real time to optimal placement of PVs at the planning stage. The dissertation is composed of three parts: the literature review, the work that has already been done and the future research tasks. An overview on renewable energy generation and its challenges are given in Chapter 1. The overall literature survey, motivation and the scope of study are also outlined in the chapter. Detailed literature reviews are given in the rest of chapters. The overvoltage and undervoltage phenomena in typical distribution networks with integration of PVs are further explained in Chapter 2. Possible approaches for voltage quality control are also discussed in this chapter, followed by the discussion on the importance of the load management for PHEVs and appliances and its benefits to electric utilities and end users. A new real power capping method is presented in Chapter 3 to prevent overvoltage by adaptively setting the power caps for PV inverters in real time. The proposed method can maintain voltage profiles below a pre-set upper limit while maximizing the PV generation and fairly distributing the real power curtailments among all the PV systems in the network. As a result, each of the PV systems in the network has equal opportunity to generate electricity and shares the responsibility of voltage regulation. The method does not require global information and can be implemented either under a centralized supervisory control scheme or in a distributed way via consensus control. Chapter 4 investigates autonomous operation schedules for three types of intelligent appliances (or residential controllable loads) without receiving external signals for cost saving and for assisting the management of possible photovoltaic generation systems installed in the same distribution network. The three types of controllable loads studied in the chapter are electric water heaters, refrigerators deicing loads, and dishwashers, respectively. Chapter 5 investigates the method to mitigate overvoltage issues at the planning stage. A probabilistic method is presented in the chapter to evaluate the overvoltage risk in a distribution network with different PV capacity sizes under different load levels. Kolmogorov–Smirnov test (K–S test) is used to identify the most proper probability distributions for solar irradiance in different months. To increase accuracy, an iterative process is used to obtain the maximum allowable injection of active power from PVs. Conclusion and discussions on future work are given in Chapter 6

Analysis of Potential and Efficiency of Electric Generation Using Thermoelectric Effect

This research identifies the electrical potential associated with Thermoelectric Generators (TEG) under the incidence of solar rays and performs efficiency comparison using this type of devices and those photovoltaic. TEG characterization and modeling is presented to favor the estimation of the electrical potential, defined as power density (W/m2). The proper operation of thermal harvesting lays in maintaining a temperature difference of at least 26.31K between the TEG sides. With this requirement fulfilled, power conversion eficiencies of about 26.43% are obtained, higher than that of high-quality solar panels and without efficiency reductions associated with heating and soiling, while keeping the same superficial area of only 16cm 2. An estimate of at least 407.3mW corresponding to 2.44Wh of available energy is found considering specific operation hours determined statistically for a given geographic location. Thus, given such performance metric, a complete power unit is devised complementing the thermoelectric energy harvesting with a Li-Po battery to guarantee in that way a continuous operation. The total energy available from the prototype allows maintaining a battery discharge percentage of 38.05% considering the energy budget of a low-power remote sensor.MaestríaMagister en Ingeniería Electrónic

Modeling, Analyses and Assessment of Microgrids Considering High Renewable Energy Penetration

Microgrids are receiving attention due to the increasing need to integrate distributed generations and to ensure power quality and provide energy surety to the customers. Since renewables need to be in the mix for energy surety, a high renewable-energy penetrated microgrid is analyzed in this paper. The standard IEEE 34 bus distribution feeder is adapted and managed as a microgrid by adding distributed generation and load profiles. The 25kV system parameters are scaled down to 12kV and renewable sources including solar PV and wind turbines, an energy storage system, and a natural gas generator have been added to the 34-bus system. The distribution generations (DG) and renewables are modeled in detail using PSCAD software and practical constraints of the components are considered. The droop control and autonomous control for microgrid normal operation in islanded mode and grid-tied mode have been proposed and studied. A novel comprehensive supervisory control scheme has been defined to manage the microgrid transition from or to the bulk grid, and to minimize the transients on voltage and frequency. Detailed analyses for islanding, reconnection, and black start are presented for various conditions. The proposed control techniques accept inputs from local measurements and supervisory controls in order to manage the system voltage and frequency. The monitoring of the microgrid for measuring power quality and control requirements for DGs and storage are modeled. The power quality issues are discussed and indexes are calculated. A novel probabilistic assessment of microgrid reliability has been proposed. At last, several extended researches are presented. An experimental system has been built which includes three 250kW inverters emulating natural gas generator, energy storage, and renewable source. The simulation and experimental results are provided which verifies the analytical presentation of the hardware and control algorithms

Development of an alternative droop strategy for controlling parallel converters in standalone DC microgrid

Most of parallel-connected DC-DC converters schemes are based on a high-bandwidth communication network to achieve minimum circulating current, proper load current sharing, and acceptable voltage regulation. However, in DC microgrids, the use of communication network can be costly and unsuitable considering the data reliability and cost investment because the load and renewable energy sources are connected to the point of common coupling. Therefore, the droop control as a decentralized method has gained more attention. However, the challenge for the conventional droop method is to overcome the issue of circulating current, poor load current sharing, and the drop in DC grid voltage due to the droop action. This thesis develops and tests an approach for minimizing the circulating current, as well as improving the voltage regulation and the load current sharing for the droop method. The developed approach is based on the concept of synchronized switching, which is implemented using an alternative droop strategy for controlling different sizes of parallel-connected DC-DC boost converters. In this thesis, synchronous switching, based on an optimized controller, is presented to eliminate the initiation of circulating current and minimize the ripple in the output current for parallel-connected boost converters. Furthermore, a modified droop method, including the cable resistance, is introduced. The modified droop method uses the measurements of the voltage and current at the point of common coupling to estimate the voltage set point for each converter locally. The communication network is eliminated by utilizing the modified droop method because, in the proposed method, there is no current and voltage measurement data transmitted from one converter to the other converter. Additional loop control is also applied for equal current sharing between parallel converters to overcome the issue of mismatch in parameters of the parallel converters. The additional loop control is added to improve the load current sharing in the modified droop control. The modified droop control method with additional loop control is verified using MATLAB/SIMULINK and validated with experimental results. However, the droop action of the modified droop and different cable resistances degrades the voltage regulation and load current sharing. Therefore, an improved droop method, which utilizes the virtual droop gain and voltage droop control gain, is proposed to overcome the problem of load current sharing and voltage regulation. The virtual droop gain compensates the differences in the cable resistances, and the voltage droop control gain regulates the voltage at the point of common coupling. This maintains the common DC bus at its rated value. The effectiveness of the improved droop method is demonstrated by MATLAB/Simulink and Laboratory prototype results. Finally, the proposed method is utilized in a standalone DC microgrid. An example of a DC microgrid of a residential building powered by a PV solar system illustrates the feasibility and the effectiveness of the proposed methods