Signal Processing and Robust Statistics for Fault Detection in Photovoltaic Arrays

abstract: Photovoltaics (PV) is an important and rapidly growing area of research. With the advent of power system monitoring and communication technology collectively known as the "smart grid," an opportunity exists to apply signal processing techniques to monitoring and control of PV arrays. In this paper a monitoring system which provides real-time measurements of each PV module's voltage and current is considered. A fault detection algorithm formulated as a clustering problem and addressed using the robust minimum covariance determinant (MCD) estimator is described; its performance on simulated instances of arc and ground faults is evaluated. The algorithm is found to perform well on many types of faults commonly occurring in PV arrays. Among several types of detection algorithms considered, only the MCD shows high performance on both types of faults.Dissertation/ThesisM.S. Electrical Engineering 201

Design of module level converters in photovoltaic power systems

The application of distributed maximum power point tracking (DMPPT) technology in solar photovoltaic (PV) systems is a hot topic in industry and academia. In the PV industry, grid integrated power systems are mainstream. The main objective for PV system design is to increase energy conversion efficiency and decrease the levelized cost of electricity of PV generators. This thesis firstly presents an extensive review of state-of-the-art PV technologies. With focus on grid integrated PV systems research, various aspects covered include PV materials, conventional full power processing DMPPT architectures, main MPPT techniques, and traditional partial power processing DMPPT architectures. The main restrictions to applying traditional DMPPT architectures in large power systems are discussed. A parallel connected partial power processing DMPPT architecture is proposed aiming to overcome existing restrictions. With flexible ‘plug-and-play’ functionality, the proposed architecture can be readily expanded to supply a downstream inverter stage or dc network. By adopting smaller module integrated converters, the proposed approach provides a possible efficiency improvement and cost reduction. The requirements for possible converter candidates and control strategies are analysed. One representative circuit scheme is presented as an example to verify the feasibility of the design. An electromagnetic transient model is built for different power scale PV systems to verify the DMPPT feasibility of the evaluated architecture in a large-scale PV power system. Voltage boosting ability is widely needed for converters in DMPPT applications. Impedance source converters (ISCs) are the main converter types with step-up ability. However, these converters have a general problem of low order distortion when applied in dc-ac applications. To solve this problem, a generic plug-in repetitive control strategy for a four-switch three-phase ISC type inverter configuration is developed. Simulation and experimental results confirm that this control strategy is suitable for many ISC converters.The application of distributed maximum power point tracking (DMPPT) technology in solar photovoltaic (PV) systems is a hot topic in industry and academia. In the PV industry, grid integrated power systems are mainstream. The main objective for PV system design is to increase energy conversion efficiency and decrease the levelized cost of electricity of PV generators. This thesis firstly presents an extensive review of state-of-the-art PV technologies. With focus on grid integrated PV systems research, various aspects covered include PV materials, conventional full power processing DMPPT architectures, main MPPT techniques, and traditional partial power processing DMPPT architectures. The main restrictions to applying traditional DMPPT architectures in large power systems are discussed. A parallel connected partial power processing DMPPT architecture is proposed aiming to overcome existing restrictions. With flexible ‘plug-and-play’ functionality, the proposed architecture can be readily expanded to supply a downstream inverter stage or dc network. By adopting smaller module integrated converters, the proposed approach provides a possible efficiency improvement and cost reduction. The requirements for possible converter candidates and control strategies are analysed. One representative circuit scheme is presented as an example to verify the feasibility of the design. An electromagnetic transient model is built for different power scale PV systems to verify the DMPPT feasibility of the evaluated architecture in a large-scale PV power system. Voltage boosting ability is widely needed for converters in DMPPT applications. Impedance source converters (ISCs) are the main converter types with step-up ability. However, these converters have a general problem of low order distortion when applied in dc-ac applications. To solve this problem, a generic plug-in repetitive control strategy for a four-switch three-phase ISC type inverter configuration is developed. Simulation and experimental results confirm that this control strategy is suitable for many ISC converters

The Sun is rising over the North Sea: Assessment of offshore solar photovoltaics

Floating solar photovoltaics (FPV), also known as floatovoltaics, is a rapidly growing application of PV systems. FPV systems are compact and occupy no land space, making them ideal for offshore deployment. This thesis explores the energy yield and integration advantages of FPV systems in detail. In the first part of the thesis, a 3.7 kW FPV system with 12 panels is modeled and compared to a land-based system, considering factors like sea waves, wind speed, and humidity. Results indicate that the FPV system yields about 13% higher annual energy output, with peaks of up to 18% in some months. Chapter 3 focuses on dynamic albedo's impact on FPV system energy generation. A varying albedo model is compared to a constant albedo model, showing a 3% performance increase with dynamic albedo. Chapter 4 assesses the feasibility of adding FPV capacity to an existing offshore wind farm in the North Sea. Cable pooling and various subsidy scenarios are considered, demonstrating economic viability under different conditions. Chapter 5 introduces a smart PV module architecture to enhance shade resilience, improving performance under partial shading conditions. The smart architecture outperforms standard series and parallel connected modules. Chapter 6 investigates the performance of a shade-resilient smart module under dynamic shading patterns. A DC-DC buck converter compensates for reduced current levels in shaded cells, resulting in efficient and consistent power output. Overall, this thesis explores the benefits and potential of FPV systems, including their energy yield, dynamic albedo effects, integration with offshore wind farms, and shade resilience using a smart module architecture

Improving the Efficiency of Energy Harvesting Embedded System

In the past decade, mobile embedded systems, such as cell phones and tablets have infiltrated and dramatically transformed our life. The computation power, storage capacity and data communication speed of mobile devices have increases tremendously, and they have been used for more critical applications with intensive computation/communication. As a result, the battery lifetime becomes increasingly important and tends to be one of the key considerations for the consumers. Researches have been carried out to improve the efficiency of the lithium ion battery, which is a specific member in the more general Electrical Energy Storage (EES) family and is widely used in mobile systems, as well as the efficiency of other electrical energy storage systems such as supercapacitor, lead acid battery, and nickel–hydrogen battery etc. Previous studies show that hybrid electrical energy storage (HEES), which is a mixture of different EES technologies, gives the best performance. On the other hand, the Energy Harvesting (EH) technique has the potential to solve the problem once and for all by providing green and semi-permanent supply of energy to the embedded systems. However, the harvesting power must submit to the uncertainty of the environment and the variation of the weather. A stable and consistent power supply cannot always be guaranteed. The limited lifetime of the EES system and the unstableness of the EH system can be overcome by combining these two together to an energy harvesting embedded system and making them work cooperatively. In an energy harvesting embedded systems, if the harvested power is sufficient for the workload, extra power can be stored in the EES element; if the harvested power is short, the energy stored in the EES bank can be used to support the load demand. How much energy can be stored in the charging phase and how long the EES bank lifetime will be are affected by many factors including the efficiency of the energy harvesting module, the input/output voltage of the DC-DC converters, the status of the EES elements, and the characteristics of the workload. In this thesis, when the harvesting energy is abundant, our goal is to store as much surplus energy as possible in the EES bank under the variation of the harvesting power and the workload power. We investigate the impact of workload scheduling and Dynamic Voltage and Frequency Scaling (DVFS) of the embedded system on the energy efficiency of the EES bank in the charging phase. We propose a fast heuristic algorithm to minimize the energy overhead on the DC-DC converter while satisfying the timing constraints of the embedded workload and maximizing the energy stored in the HEES system. The proposed algorithm improves the efficiency of charging and discharging in an energy harvesting embedded system. On the other hand, when the harvesting rate is low, workload power consumption is supplied by the EES bank. In this case, we try to minimize the energy consumption on the embedded system to extend its EES bank life. In this thesis, we consider the scenario when workload has uncertainties and is running on a heterogeneous multi-core system. The workload variation is represented by the selection of conditional branches which activate or deactivate a set of instructions belonging to a task. We employ both task scheduling and DVFS techniques for energy optimization. Our scheduling algorithm considers the statistical information of the workload to minimize the mean power consumption of the application while satisfying a hard deadline constraint. The proposed DVFS algorithm has pseudo linear complexity and achieves comparable energy reduction as the solutions found by mathematical programming. Due to its capability of slack reclaiming, our DVFS technique is less sensitive to small change in hardware or workload and works more robustly than other techniques without slack reclaiming

Optimisation, Optimal Control and Nonlinear Dynamics in Electrical Power, Energy Storage and Renewable Energy Systems

The electrical power system is undergoing a revolution enabled by advances in telecommunications, computer hardware and software, measurement, metering systems, IoT, and power electronics. Furthermore, the increasing integration of intermittent renewable energy sources, energy storage devices, and electric vehicles and the drive for energy efficiency have pushed power systems to modernise and adopt new technologies. The resulting smart grid is characterised, in part, by a bi-directional flow of energy and information. The evolution of the power grid, as well as its interconnection with energy storage systems and renewable energy sources, has created new opportunities for optimising not only their techno-economic aspects at the planning stages but also their control and operation. However, new challenges emerge in the optimization of these systems due to their complexity and nonlinear dynamic behaviour as well as the uncertainties involved.This volume is a selection of 20 papers carefully made by the editors from the MDPI topic “Optimisation, Optimal Control and Nonlinear Dynamics in Electrical Power, Energy Storage and Renewable Energy Systems”, which was closed in April 2022. The selected papers address the above challenges and exemplify the significant benefits that optimisation and nonlinear control techniques can bring to modern power and energy systems

Output Power Variation and Mismatch Losses of Photovoltaic Power Generators Caused by Moving Clouds

Photovoltaic (PV) systems are affected by irradiance fluctuations, mainly caused by overpassing cloud shadows, suffering from fluctuating output power. With high PV penetration levels, these fluctuations can lead to power system instability and problems in power quality. Further, overpassing cloud shadows cause partial shading (PS) which is the main cause of mismatch losses in PV systems. Mismatch losses occur in every PV system when interconnected PV cells have different electrical characteristics at a specific instant. Mismatch losses are mainly caused by PS but also by other differences in the operating conditions of PV modules, module damages and manufacturing tolerances. Moreover, PS can lead to failures in maximum power point tracking thereby causing extra losses.In this thesis, the output power variation and mismatch losses of PV arrays caused by the edges of moving cloud shadows are studied by simulations based on a comprehensive analysis of the measured irradiance data of the solar PV power station research plant of Tampere University of Technology. Shadings caused by moving clouds, especially the characteristics of irradiance transitions caused by the edges of cloud shadows, are analysed. For that purpose, methods to identify irradiance transitions and shading periods caused by moving clouds in measured irradiance data and a method to determine apparent shadow edge velocity were developed. A mathematical model of irradiance transitions caused by moving clouds to be used in the simulations of PV system operation was developed and verified. A parametrisation method of irradiance transitions was also developed to make the simulations of PV system operation computationally less demanding.The study of the output power variation and mismatch losses of PV arrays is conducted using the developed mathematical model of irradiance transitions and an experimentally verified MATLAB Simulink model of a PV module. The output power variation and mismatch losses of various electrical PV array configurations are studied during the irradiance transitions identified in the measured irradiance data. The effects of irradiance transition characteristics and the layout and geographic orientation of PV arrays on the output power variation and mismatch losses are studied and the overall effect of the mismatch losses caused by moving clouds on the energy production of PV plants is determined.It is shown that the electrical configuration of PV arrays has only minor effects on the output power variation and mismatch losses of the arrays. Furthermore, it is shown that the mismatch losses caused by moving cloud shadows have only a minor effect on the overall efficiency of PV arrays. Even that can be largely eliminated by minimising PV string diameters

Maximisation du transfert de l'énergie d'un champ photovoltaïque tenant compte du phénomène d'ombrage partiel : connexion réseau électrique

L’objectif de ce travail est de proposer des pistes d’optimisation, afin de minimiser les effets néfastes de l’ombrage partiel sur les systèmes des panneaux solaires photovoltaïques. Il existe dans la littérature un grand nombre de solutions pour l’extraction de la puissance maximale des panneaux solaires photovoltaïques. Dans ce mémoire, nous abordons d’un point de vue global différentes solutions nous permettant d’atteindre des rendements, fiabilités et flexibilités élevés. Ainsi la modélisation à l’aide du logiciel Matlab/Simulink nous a permis d’exposer les limites des algorithmes de suivi de puissance maximale conventionnel sous différentes conditions d’ensoleillement en utilisant les configurations de champs solaires série-parallèle et Total tied cross. Nous avons alors développé et proposé un algorithme de maximisation capable de trouver le maximum global sous n’importe quel modèle d’ombrage partiel. Ensuite deux modes de commandes associés aux convertisseurs ont été étudiés. Il s’agit de la commande droop control mise à jour utilisé pour le parallélisme de plusieurs onduleurs monophasés et la commande Proportional-integral sliding mode pour le contrôle d’onduleurs triphasés. Ces commandes vont d’une part faciliter l’intégration accrue des systèmes solaires photovoltaïques au réseau tout en assurant une bonne qualité de l’énergie et d’autre part vont garantir un transfert optimisé de la production lors des phénomènes d’ombrage partiel. Nous avons également étudié la topologie des micro-onduleurs qui permet de minimiser l’impact négatif des ombrages partiels pour les installations de faibles puissances. Nous avons analysé le fonctionnement de deux types de micro-onduleurs avec isolation galvanique : le flyback et le boost à double inductance

Industrial Applications: New Solutions for the New Era

This book reprints articles from the Special Issue "Industrial Applications: New Solutions for the New Age" published online in the open-access journal Machines (ISSN 2075-1702). This book consists of twelve published articles. This special edition belongs to the "Mechatronic and Intelligent Machines" section

A new method of analyzing the photovoltaic power plant works under variation of solar radiation

Rad se bavi problemom smanjenja proizvodnje električne energije fotonaponske elektrane u uslovima promenljivog zračenja. Predlaže se novi metod analize rada u uslovima senčenja putem makro- i mikrorekonfiguracije FN polja, koja povećava proizvodnju električne energije.The paper presents the problem of reducing electricity production of PV power plant under variation of solar radiation conditions. The author proposed a new method of analysis PV power plant works under partial shading condition trough micro- and macroconfiguration of PV array

Management: A continuing bibliography with indexes, March 1983

This bibliography lists 960 reports, articles, and other documents introduced into the NASA scientific and technical information system in 1982