Comparative Study of Maximum Power Point Tracking Techniques for Photovoltaic Systems

The generation of electricity from photovoltaic (PV) arrays has been increasingly considered as a prominent alternative to fossil fuels. However, the conversion efficiency is typically low and the initial cost is still appreciable. A required feature of a PV system is the ability to track the maximum power point (MPP) of the PV array. Besides, MPP tracking (MPPT) is desirable in both grid-connected and stand-alone photovoltaic systems because the solar irradiance and temperature change throughout the day, as well as along seasons and geographical conditions, also leading to the modification of the I×V (current versus voltage) and P×V (power versus voltage) curves of the PV module. MPPT is also justified by the relatively high cost of the energy generated by PV systems if compared with other sources. Since there are various MPPT approaches available in the literature, this work presents a comparative study among four popular techniques, which are the fixed duty cycle method, constant voltage (CV), perturb and observe (P&O), and incremental conductance (IC). It considers different operational climatic conditions (i.e., irradiance and temperature), since the MPP is nonlinear with the environment status. PSIM software is used to validate the assumptions, while relevant results are discussed in detail

Study and implementation of high power factor three-level rectifiers employing soft switching techniques

This thesis proposes the study of single-phase and three-phase three-level rectifiers operating with unity power factor. By the investigation of several works in the literature, prominent characteristics such as minimized conduction losses, reduced number of components and low harmonic content of the input current can be addressed to the topologies. They are studied in order to determine the operating conditions and define the design procedure for power and control circuits. Furthermore, a passive lossless snubber is proposed to minimize switching losses, improving efficiency. Finally, analytical results are presented so that the performance of the converters can be evaluated, and important issues are discussed.Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorDoutor em CiênciasEsta tese propõe o estudo dos retificadores monofásico e trifásico a três níveis operando com fator de potência unitário. Através da análise de diversos trabalhos existentes na literatura, pode-se atribuir a estas estruturas as características de baixas perdas por condução, utilização de um menor número de componentes e conteúdo harmônico reduzido da corrente de entrada. Inicialmente, estas topologias são estudadas de forma a determinar as respectivas condições de operação e definir a metodologia de projeto dos estágios de potência e controle. Com o intuito de minimizar as perdas por comutação em tais conversores, propõe-se uma célula de comutação suave utilizando apenas elementos passivos como indutores, capacitores e diodos. Por fim, apresenta-se resultados analíticos que possibilitam a investigação do desempenho dos retificadores, no intuito de promover discussões técnicas do tema em questão

Uma fonte chaveada de fator de potência na forma de fonte simétrica.

This paper proposes a switched-mode power supply (SMPS) with power factor correction. A preregulator boost converter is employed in order to obtain universal line voltage and reduced harmonic content of the input current. Two dc/dc forward converters are used so that two symmetrical output stages are obtained. The association of the aforementioned ac/dc and dc/dc converters results in a high power factor SMPS.Este trabalho propõe a concepção de uma fonte chaveada com correção de fator de potência, obtida através de uma integração de soluções, ou seja, a associação de um conversor ca/cc e dois conversores cc/cc. Um estágio ca;cc pré-regulador do tipo boost é utilizado, obtendo-se tensão de alimentação universal e conteúdo harmônico reduzido da corrente de entrada. Dois conversores forward são empregados na conversão cc/cc de forma a se obter dois estágios na forma de fonte simétrica

Uma fonte chaveada de fator de potência na forma de fonte simétrica.

This paper proposes a switched-mode power supply (SMPS) with power factor correction. A preregulator boost converter is employed in order to obtain universal line voltage and reduced harmonic content of the input current. Two dc/dc forward converters are used so that two symmetrical output stages are obtained. The association of the aforementioned ac/dc and dc/dc converters results in a high power factor SMPS.Este trabalho propõe a concepção de uma fonte chaveada com correção de fator de potência, obtida através de uma integração de soluções, ou seja, a associação de um conversor ca/cc e dois conversores cc/cc. Um estágio ca;cc pré-regulador do tipo boost é utilizado, obtendo-se tensão de alimentação universal e conteúdo harmônico reduzido da corrente de entrada. Dois conversores forward são empregados na conversão cc/cc de forma a se obter dois estágios na forma de fonte simétrica

Thermal Analysis of Power Converters for DFIG-Based Wind Energy Conversion Systems during Voltage Sags

The doubly fed induction generator (DFIG) and back-to-back converter are very sensitive to power quality disturbances in grid-connected wind energy conversion systems (WECSs). Special attention has been given to protect the system from voltage sags, considering the introduction of several low-voltage ride-through (LVRT) techniques in the literature. However, only few works have really analyzed the behavior of power semiconductors during such phenomena in terms of the thermal stresses, whereas the existing studies are focused on balanced voltage sags only. In this context, this work presents a thermal profile analysis of power semiconductors in the grid-side converter (GSC) and rotor-side converter (RSC) considering a DFIG-based WECS submitted to symmetrical and asymmetrical voltage sags. The system is modeled using PLECS software and results on a 2.0 MW system are presented and thoroughly discussed. The results show that it is possible to meet the ride-through requirements during both balanced and unbalanced sags in terms of acceptable thermal stresses on the semiconductors as long as the back-to-back converter and its respective control system are properly designed

Switched Capacitor DC-DC Converters: A Survey on the Main Topologies, Design Characteristics, and Applications

This work presents a review of the main topologies of switched capacitors (SCs) used in DC-DC power conversion. Initially, the basic configurations are analyzed, that is, voltage doubler, series-parallel, Dickson, Fibonacci, and ladder. Some aspects regarding the choice of semiconductors and capacitors used in the circuits are addressed, as well their impact on the converter behavior. The operation of the structures in terms of full charge, partial charge, and no charge conditions is investigated. It is worth mentioning that these aspects directly influence the converter design and performance in terms of efficiency. Since voltage regulation is an inherent difficulty with SC converters, some control methods are presented for this purpose. Finally, some practical applications and the possibility of designing DC-DC converters for higher power levels are analyzed

Wheel Slip Control Applied to an Electric Tractor for Improving Tractive Efficiency and Reducing Energy Consumption

This work presents an automatic slip control solution applied to a two-wheel-drive (2WD) electric tractor. Considering that the slip can be maintained within a specific range that depends on the type of soil, it is possible to increase the tractive efficiency of the electric vehicle (EV). The control system can be easily designed considering only the longitudinal dynamics of the tractor while using simple proportional-integral (PI) controllers to drive the inverters associated with the rear wheels. The introduced solution is tested on an experimental electric tractor prototype traveling on firm soil considering case studies in which the slip control is enabled and disabled. The acquired results demonstrate that the slip control allows for obtaining a more stable performance and reduced energy consumption

Um conversor forward a duas chaves associada a um conversor boost quadrático e nova característica de conversor a duas chaves.

This paper presents a topology of two-switch Forward converter associated with a quadratic Boost converter, which provides large voltage step-up (from 12V to 80V). The combination of the stages results in a switched-mode power supply (SMPS) whose output voltages are +200V and -200V. The operation of both converters is analyzed, as some results concerning the proposed SMPS are presented.Este trabalho propõe uma topologia de conversor Forward a duas chaves associada a um conversor Boost quadrático, que apresenta a característica de ampla elevação da tensão de entrada, ou seja, de 12V para 80V. A combinação destes estágios resulta em uma fonte chaveada em que as tensões de saída são +200V e -200V. A operação dos conversores é analisada e resultados são apresentados para validar a proposta

A DC-DC converter based on the three-state switching cell for high current and voltage step-down applications

This paper presents a pulsewidth modulation dc-dc nonisolated buck converter using the three-state switching cell, constituted by two active switches, two diodes, and two coupled inductors. Only part of the load power is processed by the active switches, reducing the peak current through the switches to half of the load current, as higher power levels can then be achieved by the proposed topology. The volume of reactive elements, i.e., inductors and capacitors, is also decreased since the ripple frequency of the output voltage is twice the switching frequency. Due to the intrinsic characteristics of the topology, total losses are distributed among all semiconductors. Another advantage of this converter is the reduced region for discontinuous conduction mode when compared to the conventional buck converter or, in other words, the operation range in continuous conduction mode is increased, as demonstrated by the static gain plot. The theoretical approach is detailed through qualitative and quantitative analyses by the application of the three-state switching cell to the buck converter operating in nonoverlapping mode $(D < 0.5)$. Besides, the mathematical analysis and development of an experimental prototype rated at 1 kW are carried out. The main experimental results are presented and adequately discussed to clearly identify its claimed advantages. © 1986-2012 IEEE