A mismatch in a photovoltaic array implies differences in the I-V characteristics of the modules forming the array which can lead to significant energy losses known as mismatch losses. The sources of mismatch losses could be easy- or difficult-to-predict sources. This thesis proposes novel designs for photovoltaic arrays to reduce mismatch losses. The mismatch from easy-to-predict sources and its resulting losses can be reduced by altering the interconnection of the array. Therefore, this thesis proposes an optimal total-cross-tied interconnection, based on a thorough mathematical formulation, which can significantly reduce mismatch losses from easy-to-predict sources. Application examples of the operation of the optimal total-cross-tied interconnection under partial shading are presented. The effect of partial shading caused by easy- or difficult-to-predict sources can be considerably reduced by photovoltaic array reconfiguration. This thesis proposes a novel mathematical formulation for the optimal reconfiguration of photovoltaic arrays to minimize partial shading losses. The thesis formulates the reconfiguration problem as a mixed integer quadratic programming problem and finds the optimal solution using branch-and-bound algorithm. The proposed formulation can be used for equal or non-equal number of modules per row. Moreover, it can be used for fully reconfigurable or partially-reconfigurable arrays. Application examples of the operation of the reconfigurable photovoltaic array under partial shading are presented. Finally, the recently updated American National Electric Code requires the presence of a series arc fault detector in any Photovoltaic installation operating at a voltage greater than or equal to 80V. However, the Photovoltaic market nowadays lacks the presence of an accurate series arc fault detector that can detect series arc faults and discriminate between them and partial shading. The work in this thesis proposes an algorithm that can detect series arc faults and discriminate between them and partial shading in total-cross-tied arrays. This algorithm is based on the measurement of instantaneous row voltages.

Αντικείμενο της παρούσας διπλωματικής εργασίας είναι η μελέτη λειτουργίας των φωτοβολταϊκών γεννητριών υπό συνθήκες χαμηλής έντασης ακτινοβολίας όχι όμως ελεγχόμενης, δηλαδή σε εσωτερικό χώρο, αλλά εκτεθειμένο σε εξωτερικό χώρο και με απρόβλεπτες εναλλαγές έντασης. Επιπλέον το υποβάλαμε σε μερική σκίαση με διαφορετική διάταξη κάθε φορά προκειμένου να διαπιστώσουμε τη λειτουργία του και το πώς αυτό συμπεριφέρεται, προκειμένου να κατανοήσουμε το πόσο σημαντικό είναι να ακολουθούνται οι προδιαγραφές εγκατάστασης για να παίρνουμε την μέγιστη απόδοση από τις φωτοβολταϊκές γεννήτριες. Για το σκοπό αυτό είχαμε στη διάθεσή μας ένα φωτοβολταϊκό πλαίσιο, το οποίο αποτελούνταν από 36 στοιχεία και μια βάση κινητή για να το τοποθετήσουμε με σκοπό να το προσανατολίζουμε σωστά ακολουθώντας την πορεία του ηλίου και την οποία την κατασκευάσαμε εξ αρχής. Στη συνεχεία απαραίτητη ήταν η κατασκευή δύο κυκλωμάτων, ενός “I-V tracer” και ενός “Ramp Generator” μέσα στο ίδιο κουτί, προκειμένου να συνδέσουμε επάνω σε αυτό όλες τις συσκευές μας για να καταγράψουμε τις σειρές των μετρήσεών μας που μας έδιναν οι διάφορες συσκευές μας καθώς και το φωτοβολταϊκό κατά τη διάρκεια της έκθεσής του στην ηλιακή ακτινοβολία. Ακόμα, σημαντικό κομμάτι αποτέλεσε και ο προγραμματισμός του Data Logger έτσι ώστε να καταγράφονται σωστά η τάση, το ρεύμα, οι θερμοκρασίες και η ακτινοβολία κάθε στιγμή του πειράματός μας για να τα εκμεταλλευτούμε και να εξαγάγουμε σωστά συμπεράσματα. Τέλος μπορούμε να πούμε πως η επιλογή ιδανικών ημερών ήταν ένα δύσκολο κομμάτι και η υπομονή που απαιτούσε το πείραμά μας ήταν ένας καλός σύμμαχος για την ολοκλήρωσή του. / -

It is essential to always track maximum power from photovoltaic (PV) sources. Failure to track the global maximum power point under partial shading conditions is one of the major reasons that lead to significant power losses. Several maximum power point tracking methods have been proposed to deal with this problem. However, none of them were able to effectively identify the occurrence of partial shading. With the facility of Matlab modelling and simulation as well as the aid of a constructed solar emulator, the power-voltage characteristics of a PV panel under uniform and non-uniform irradiance conditions have been studied and some useful conclusions have been identified from observation. Based on these conclusions, a novel maximum power point tracking algorithm has been proposed, which is capable of identifying the occurrence of partial shading hence determining the need for a global scan over the operation range of PV panels for the true maximum power point. In the meantime, the effect of PV dynamics, due to the capacitance of PV cells, on maximum power point trackers has been investigated and some initial results and suggestions have been presented in this work.

This dissertation examines the application of various classical root finding methods to digital maximum power point tracking (DMPPT). An overview of root finding methods such as the Newton Raphson Method (NRM), Secant Method (SM), Bisection Method (BSM), Regula Falsi Method (RFM) and a proposed Modified Regula Falsi Method (MRFM) applied to photovoltaic (PV) applications is presented. These methods are compared among themselves. Some of their features are also compared with other commonly used maximum power point (MPP) tracking methods. Issues found when implementing these root finding methods based on continuous variables in a digital domain are explored. Some of these discussed issues include numerical stability, digital implementation of differential operators, and quantization error. Convergence speed is also explored. The analysis is used to provide practical insights into the design of a DMPPT based on classical root finding algorithms. A new DMPPT based on a MRFM is proposed and used as the basis for the discussion. It is shown that this proposed method is faster than the other discussed methods that ensure convergence to the MPP. The discussion is approached from a practical perspective and also includes theoretical analysis to support the observations. Extensive simulation and experimental results with hardware prototypes verify the analysis. / text

The Gold Tree Solar Farm, designed by REC Solar, has a rated output power of 4.5 MW and began operation in 2018 to provide electricity to Cal Poly’s campus. Gold Tree Solar Farm site terrain consists of rolling hills and uneven slopes. The uneven typography results in interrow shading, requiring a modified tracking control algorithm to maximize power production. Predicting a utility solar field’s lifetime energy yield is a critical step in assessing project feasibility and calculating project revenue. The MATLAB-based predictive power model developed for this field overpredicted power in the middle of the day. The purpose of this thesis was to develop a point-in-time power routine to run through experimental data collected from the Gold Tree Solar Farm and compare different cell temperature and degradation models in an effort to correct this overprediction. Increasing cell temperature reduces power output of a solar panel, and an objective of this analysis was to find a model that accurately predicted cell temperature to calculate this loss. Seven cell temperature models were adjusted to fit the specifications of the Gold Tree Solar Farm and compared to thermocouple measurements from the field. Frequent partial shading, which results in thermal cycling, contributes to accelerated module degradation and power loss. Yearly and seasonal plant degradation rates driven by environmental factors such as temperature, UV radiation, and relative humidity were calculated and integrated into the predictive power model.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work presents a study and analysis of photovoltaic systems subject to partial shading, where the main consequence is the reduction of its energy production. To mitigate this problem, it is proposed a new photovoltaic architecture known as hybrid architecture. In this architecture, the system is separated into arrays that can be partially or completely shaded with other arrays that are not shaded. The partially shaded modules are connected in parallel to maximize its energy production, while unshaded ones are connected in series. A dc-dc converter is used with the array with the modules subject to partial shading for maximum power extraction of this array, to match the operating voltage of both arrays, and to ensure that during its operation, the unshaded array operates in maximum power point. Additionally, it is presented the small signal modeling of the dc-dc converter through the generalized modeling technique, with the inclusion of the dynamic of a photovoltaic array through an equivalent approximate model by a voltage source with a series resistance, and linearized for different curve points of the photovoltaic module. The proposed control system for this converter uses a controller based on the internal model principle, as the resonant one, whose objective is, besides eliminating the low frequency ripple at the input of photovoltaic module to reduce the losses of the maximum power point tracking algorithm, also reduce the dc-bus capacitance in dual-stage photovoltaic inverters. Shaded photovoltaic systems present higher complexity to predict its energy production. This is because there are different configurations to connect photovoltaic modules among each other, which results in different values of generated power. Consequently, a general methodology of energy production forecast that uses only the shaded area of the modules as a factor of analysis can be imprecise. Based on this, a new methodology for energy production forecast in partially shaded photovoltaic systems is presented. The proposed method consists in identifying the shaded modules in each time, to quantify the hourly irradiation incident on all modules, analyze the electrical configuration of the array and, from that, calculate the produced energy. At the end are presented simulation and experimental results that validate the use of hybrid architecture in photovoltaic systems that present partial shading conditions. / Este trabalho apresenta um estudo e análise de sistemas fotovoltaicos que apresentam redução da produção de energia devido ao sombreamento parcial em módulos fotovoltaicos. Para mitigar este problema, é proposta uma nova arquitetura de sistemas fotovoltaicos denominada arquitetura híbrida. Nessa arquitetura, o sistema é separado em um arranjo de módulos que podem ser parcialmente ou totalmente sombreados e outro com módulos não-sombreados. Os módulos do arranjo passíveis de sombreamento são conectados em paralelo entre si para se maximizar sua produção de energia, enquanto que os módulos não-sombreados são arranjados em série. Um conversor CC-CC é empregado junto ao arranjo dos módulos passíveis de sombreamento para extração da máxima potência desse arranjo, para compatibilizar a tensão de operação dos dois arranjos, e para garantir que durante a operação conjunta, o arranjo que nunca é sombreado opere no ponto de máxima potência. Adicionalmente, obtém-se a modelagem de pequenos sinais do conversor CC-CC através da modelagem generalizada, com a inclusão da dinâmica de um arranjo fotovoltaico através de um modelo equivalente aproximado por uma fonte de tensão em série com uma resistência, e linearizado para diversos pontos da curva do painel. Como proposta de sistema de controle desse conversor, utiliza-se um controlador baseado no princípio do modelo interno, como o ressonante, cujo objetivo é, além de eliminar a ondulação em baixa frequência presente na entrada dos painéis para reduzir as perdas do algoritmo de rastreamento do ponto de máxima potência, também possibilitar a redução da capacitância do barramento CC de inversores de duplo estágio. Sistemas fotovoltaicos sombreados apresentam maior complexidade para se prever a produção de energia. Isso ocorre pois existem diversas configurações para se conectar os módulos fotovoltaicos entre si, cujo impacto resulta em diferentes valores da energia gerada. Por consequência, uma metodologia generalizada de previsão da produção de energia que utilize apenas a área sombreada dos módulos como fator de análise pode ser pouco precisa. Com base nisso, uma nova metodologia para previsão da produção de energia em sistemas fotovoltaicos parcialmente sombreados é apresentada. O método proposto consiste em identificar os módulos sombreados em cada hora, quantificar a irradiação horária incidente em todos os módulos, analisar a configuração elétrica do arranjo e, a partir disso, calcular a energia produzida. Por fim são apresentados resultados de simulação e experimentais que validam a utilização da arquitetura híbrida em sistemas fotovoltaicos que apresentam condições de sombreamento parcial.

This thesis deals with quantifying the merits of Distributed Maximum Power Point Tracking (DMPPT), as well as providing solutions to achieve DMPPT in PV systems. A general method based on 3D modeling is developed to determine the energy yield of PV installations exploiting different levels of DMPPT granularity. Sub-string-level DMPPT is shown to have up to 30% more annual energy yield than panel-level DMPPT. A Multi-Input-Single-Output (MISO) dc-dc converter is proposed to achieve DMPPT in parallel-connected applications. A digital current-mode controller is used to operate the MISO converter in pseudo-CCM mode. For series-connected applications, the virtualparallel concept is introduced to utilize the robustness of the parallel connection. This concept is demonstrated on a three-phase boost converter. The topology offers reduced output voltage ripple under shading which increases the life-time of the output capacitor. The prototypes yield output power benefits of up to 46% and 20% for the tested shading conditions.

This thesis deals with quantifying the merits of Distributed Maximum Power Point Tracking (DMPPT), as well as providing solutions to achieve DMPPT in PV systems. A general method based on 3D modeling is developed to determine the energy yield of PV installations exploiting different levels of DMPPT granularity. Sub-string-level DMPPT is shown to have up to 30% more annual energy yield than panel-level DMPPT. A Multi-Input-Single-Output (MISO) dc-dc converter is proposed to achieve DMPPT in parallel-connected applications. A digital current-mode controller is used to operate the MISO converter in pseudo-CCM mode. For series-connected applications, the virtualparallel concept is introduced to utilize the robustness of the parallel connection. This concept is demonstrated on a three-phase boost converter. The topology offers reduced output voltage ripple under shading which increases the life-time of the output capacitor. The prototypes yield output power benefits of up to 46% and 20% for the tested shading conditions.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-09-12T14:19:20Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Artur_Muniz_Dissertacao_Digital_Biblioteca.pdf: 14042205 bytes, checksum: 21290a8d10774b2848f16e9351043b9a (MD5) / Made available in DSpace on 2016-09-12T14:19:20Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Artur_Muniz_Dissertacao_Digital_Biblioteca.pdf: 14042205 bytes, checksum: 21290a8d10774b2848f16e9351043b9a (MD5) Previous issue date: 2016-02-26 / FACEPE / A curva da potência em função da tensão nos terminais de uma conexão em série de módulos fotovoltaicos, com diodos de passagem protetores, exposta a um sombreamento parcial, exibe um comportamento com múltiplos picos. Os múltiplos picos tornam as estratégias clássicas de seguimento do ponto de máxima potência, ou MPPT, ineficazes. Em primeiro momento, este trabalho realiza uma análise estatística que determina uma região trapezoidal no plano tensão potência onde o ponto de máxima potência global está inserido para qualquer situação de irradiâncias múltiplas e temperatura, para configurações com inversor central e módulos conectados em séries puras ou conectadas em paralelo. Em segundo momento, este trabalho pesquisa as técnicas de MPPT Global que rastreiam o ponto de máxima potência global de uma curva tensão potência com múltiplos picos. Duas destas técnicas são estudadas a fim de avaliar a rapidez em encontrar o ponto de máxima potência global e a energia perdida na busca. Por fim, é proposta uma nova técnica de MPPT Global baseada no estudo estatístico preliminar. Esta nova técnica é proposta tirando proveito do trapézio delimitado na análise estatística. / The power-voltage characteristic of series arrays of photovoltaic modules with bypass diodes under partial shading conditions, displays a multiple peaks behavior. The multiple peaks make the classical algorithms of maximum power point tracking, or MPPT, ineffective. At first, this work performs a statistical analysis that determines a trapezoidal region in the power voltage plan where the global maximum power point is situated for any situation from multiple irradiances and any temperature, for central inverter configuration with a series array of modules or parallel connected series arrays. Soon after, this paper researches the Global MPPT techniques that track the global maximum power point of power-voltage curves with multiple peaks. Some of these techniques are studied to assess how fast they can find the global maximum power point and the energy lost at this search. Finally, it is proposed a new Global MPPT technique based on the preliminary statistical study. This new technique is proposed taking advantage of the trapezoidal region defined in the statistical analysis.

The necessity for clean and sustainable energy has shifted the energy sector’s interest in renewable energy sources. Photovoltaics (PV) is the most popular renewable energy source because the sun is ubiquitous. However, several discrepancies exist in a PV system when implemented for real-world applications. Among several other existing problems related to Photovoltaics, in this work, we deal with maximum power point tracking (MPPT) under Partial Shading (PS) conditions. MPPT is a mechanism formulated as an optimization problem adjusting the PV to deliver the maximum power to the load. Under full insolation conditions, varying solar panel temperatures, and different loads MPPT problem is a convex optimization problem. However, when the PV’s surface is partially shaded, multiple power peaks are created in the power versus voltage (P-V) curve making MPPT non-convex.