Estimação do Conteúdo Eletrônico Total da Ionosfera Utilizando Geoestatística

http://dx.doi.org/10.5902/2179460X14862Ionosphere is the ionizable atmosphere layer, where physical and chemical processes result in atoms ionization and neutralization,which interact with Earth’s magnetic field and generate regions with different electronic concentration. The ionizationdistribution in ionosphere affects mainly telecommunications, and may cause distortions and systems failure such as GlobalPositioning System (GPS). In this work, Total Electronic Content (TEC) data is used, observed at several double frequencyGPS stations over South America, to estimate TEC in the whole region, including locations where these measures are not available.The geostatistic techniques ordinary kriging and gaussian sequential simulation were applied, using the software StanfordGeostatistical Modeling Software (SGEMS), and presented similar and coherent results.A ionosfera é a camada ionizável da atmosfera, onde ocorrem processos físicos e químicos que resultam na ionização e neutralização de átomos, que interagem com o campo magnético terrestre e geram regiões com maior ou menor concentração eletrônica. A distribuição de ionização presente na ionosfera afeta principalmente as telecomunicações, podendo causar distorções e falhas em sistemas como o Sistema Global de Posicionamento (GPS). Neste trabalho, são utilizados dados de Conteúdo Eletrônico Total (TEC) observados através de estações de GPS de dupla frequência, espalhadas na América do Sul, para estimação do TEC em toda a região, incluindo as localidades que não dispõem dessas medições. Para isso, foram aplicadas as técnicas geostatísticas krigagem ordinária e simulação sequencial gaussiana através da ferramenta de software Stanford Geostatistical Modeling Software (SGEMS), que apresentaram resultados similares e coerentes

Inversor Quasi-Z-Source Fotovoltaico Conectado à Rede com Filtro LCL Utilizando Uma Estrutura MRAC-SM Cascata com Modelo Reduzido para Aplicações em Redes Fracas

Este trabalho propõe a utilização de uma estrutura cascata de controladores adaptativos do tipo entrada-saída por modelo de referência (MRAC) utilizando modelos de ordem reduzida para um inversor quasi-Z-Source, conectado à rede por meio de um filtro LCL. A implementação da estrutura adaptativa por meio de modelos de referência reduzidos possibilita um sistema de controle adaptativo mais simples de ser implementado, com equacionamento matemático reduzido e menor esforço computacional. Para a redução da ordem dos modelos de referência, dinâmicas presentes em frequências mais elevadas da planta não são consideradas para projeto do controlador, possibilitando a implementação de uma estrutura simplificada que não comprometa a estabilidade e o desempenho do sistema. Resultados online em Hardware-In-the-Loop implementados em um DSP TMS320F28335 são apresentados, comparando a estrutura proposta com um controlador MRAC-SM por realimentação de estados sem simplificação de modelos. É mostrado que a estrutura adaptativa desenvolvida se comporta de forma robusta em relação às incertezas, apresenta baixo erro de rastreamento e carga computacional reduzida quando comparada com a estrutura adaptativa sem redução do modelo de referência

A new discrete-time Robust Adaptive Predictive Control-based RMRAC applied to grid connected converters with LCL Filter / Um novo controlador preditivo robusto adaptativo baseado em RMRAC em tempo discreto aplicado a conversores conectados à rede com filtro LCL

In this work, is developed a new discrete-time robust adaptive predictive control based on combining the adaptive structure of a Model Reference Adaptive Controller  (MRAC),  to adjust gains online, with the control law One Sample Ahead Preview (OSAP), a particular case of deadbeat controller, for the current loop of a grid-connected voltage-source converter, also,  this control not need resonant controllers to reject exogenous disturbances. A case application is presented, the grid-side currents control of a three-phase full-bridge static converter connected to the electrical grid by LCL filter. Simulation results are presented to show the performance of the proposed controller in a grid connected system

Grid-Connected Converters: A Brief Survey of Topologies, Output Filters, Current Control, and Weak Grids Operation

Grid-connected converters (GCCs) are used extensively for the integration of DC power sources with AC power sources. However, since it is a complex topic, there are many possibilities for regulating grid-injected currents, as well as different modulation techniques for generating full-bridge PWM voltages. The control techniques are directly related to the type of output filter, as well as to the topology of the converter, since a complex plant can require more sophisticated controllers to keep the system stable, and with good regulation performance. Furthermore, a discussion of the applicability of these converters in weak and very weak grids with high inductance content has recently been growing, which adds a greater degree of complexity to the control structure of the converter. In this brief overview are outlined some topics about topologies, output filters, and control, focusing on the current regulation of grid-connected converters. In addition, a discussion of the main challenges and critical areas in operating on weak and very weak grids is also presented

An RMRAC With Deep Symbolic Optimization for DC–AC Converters Under Less-Inertia Power Grids

This paper presents a novel approach for grid-injected current control of DC-AC converters using a robust model reference adaptive controller (RMRAC) with deep symbolic optimization (DSO). Grid voltages are known to be time-varying and can contain distortions, unbalances, and harmonics, which can lead to poor tracking and high total harmonic distortion (THD). The proposed adaptive control structure addresses this issue by enabling or disabling harmonics compensation blocks based on the grid voltage’s characteristics. The DSO framework is implemented to generate an equivalent mathematical expression of the grid voltages, which is then incorporated into the RMRAC-based controller. The controller is then able to reconfigure itself to adequately compensate for high harmonics present in the grid, reducing computational complexity and improving performance. A controller-hardware-in-the-loop (C-HIL) environment with a Typhoon HIL 604 and a TSM320F28335 DSP is implemented to demonstrate that the proposed RMRAC-based structure with DSO outperforms both the same adaptive structure without DSO and a superior RMRAC-based controller. The proposed approach has potential applications in less-inertia power grids, where efficient and accurate control of grid-connected converters is crucial

Control Methodologies to Mitigate and Regulate Second-Order Ripples in DC–AC Conversions and Microgrids: A Brief Review

Second-order ripples occur in the voltage and current during any DC–AC power conversion. These conversions occur in the voltage source inverters (VSIs), current source inverters (CSIs), and various single-stage inverters (SSIs) topologies. The second-order ripples lead to oscillating source node currents and DC bus voltages when there is an interconnection between the AC and DC microgrids or when an AC load is connected to the DC bus of the microgrid. Second-order ripples have various detrimental effects on the sources and the battery storage. In the storage battery, they lead to the depletion of electrodes. They also lead to stress in the converter or inverter components. This may lead to the failure of a component and hence affect the reliability of the system. Furthermore, the second-order ripple currents (SRCs) lead to ripple torque in wind turbines and lead to mechanical stress. SRCs cause a rise in the temperature of photovoltaic panels. An increase in the temperature of PV panels leads to a reduction in the power generated. Furthermore, the second-order voltage and current oscillations lead to a varying maximum power point in PV panels. Hence, the maximum power may not be extracted from it. To mitigate SRCs, oversizing of the components is needed. To improve the lifespan of the sources, storage, and converter components, the SRCs must be mitigated or kept within the desired limits. In the literature, different methodologies have been proposed to mitigate and regulate these second-order ripple components. This manuscript presents a comprehensive review of different effects of second-order ripples on different sources and the methodologies adopted to mitigate the ripples. Different active power decoupling methodologies, virtual impedance-based methodologies, pulse width modulation-based signal injection methodologies, and control methods adopted in distributed power generation methods for DC microgrids have been presented. The application of ripple control methods spans from single converters such as SSIs and VSIs to a network of interconnected converters. Furthermore, different challenges in the field of virtual impedance control and ripple mitigation in distributed power generation environments are discussed. This paper brings a review regarding control methodologies to mitigate and regulate second-order ripples in DC–AC conversions and microgrids

Performance comparison of discrete-time robust adaptive controllers for grid-tied power converters under unbalanced grids

Renewable energy generation systems largely use grid-tied power converters with LCL filters. A well-known issue in this kind of system is the resonance of the LCL filter, whose frequency is straightforwardly affected by grid condition. Variations on grid impedance tends to make the controller performance poor and until turn the closed-loop unstable. Therefore, some controllers are designed for specific operation ranges to ensure performance and global stability. However, a deep study of Model Reference Adaptive-based Controllers for this kind of issue was not conducted yet. The aim of this paper is to fit this research gap. Thus, this paper presents a performance comparison of feasible discrete-time robust adaptive controllers, based on reduced order reference model, for grid-tied power converters with LCL filter under unbalanced grid conditions, providing an assessment of the benefits and drawbacks of each considered control strategy. The evaluated control laws are: Robust Model Reference Adaptive Controller, Robust Model Reference-based Adaptive Super-Twisting Sliding Mode Controller, Robust Adaptive One Sample Ahead Preview Controller, and Robust Adaptive Proportional-Integral Controller. Through performance comparison, it can be defined what controller is more adequate in face of grid condition, taking into consideration grid-injected currents quality and design complexity of controller. Experimental results of grid-injected current control of a grid-tied 5.8 kW Voltage-Source Inverter with LCL filter considering relevant grid voltage unbalance are presented to corroborate the controllers’ performance and discuss their reference tracking response, robustness to the parametric variation, exogenous disturbance rejection, parameters adaptability, and global stability. In evaluated scenarios, Robust Adaptive Proportional-Integral controller presented slower regulation dynamics between compared adaptive structures, but reduced tracking error, as well as lower total harmonics distortion, while Robust Model Reference-based Adaptive Super-Twisting Sliding Mode Controller has the smaller overshoot in the initial transient regime, as well as the shorter transient regime