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URI permanente para esta colecciónhttps://hdl.handle.net/10953/230

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Power Gain and Daily Improvement Factor in Stand-Alone Photovoltaic Systems With Maximum Power Point Tracking Charge Regulators. Case of Study: South of Spain
(American Society of Mechanical Engineers, 2013-11) Muñoz-Rodríguez, Francisco José; Jiménez-Castillo, Gabino; Fuentes-Conde, Manuel; Aguilar-Peña, Juan Domingo
The performance reliability of a stand-alone photovoltaic system (SAPV) depends on the long-term performance of the batteries. In this way, a charge controller becomes an essential device which not only prevents the batteries from suffering deep discharges and overvoltages but also monitors the battery state of charge (SOC) in order to maximize charging efficiency and energy availability. At present, pulse width modulated (PWM) charge regulators dominate the market for this type of component in SAPV systems. However, in recent years, to improve energy management, more manufacturers have developed controllers with strategies for maximum power point tracking (MPPT). PWM charge controllers do not always make optimum use of the available power given by the maximum power point and this gives a loss of power. These power losses depend on battery voltage, irradiance and temperature. However, they can be avoided by using a MPPT charge controller which operates the array at its maximum power point under a range of operating conditions, as well as regulating battery charging. The advantage, in terms of energy gain, provided by this type of charge regulator depends on weather conditions. This paper will study the power gain provided by this type of charge controller, depending on the module temperature and the battery voltage. The paper will, additionally, provide a study of the gain in energy yield, also shown as improvement factor, F, for SAPV systems installed in Jaén (South of Spain). This study may illustrate the behavior of these two types of charge controllers in warm weathers, like Mediterranean climates. Furthermore, it will analyze the suitability of MPPT charge controllers and their benefits in this type of climate. It will be shown that MPPT charge regulator global efficiency constitutes a key issue in making a choice between MPPT and PWM charge regulators. The results given here may be not only of interest for SAPV systems with no access to the electricity grid but also for battery back-up PV grid-connected PV (GCPV) systems.
Development of combined Runge–Kutta Broyden's load flow approach for well- and ill-conditioned power systems
(Wiley, 2018-11) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
Load flow (LF) is an extensively used tool in planning and operation of power systems. Formulation of LF problem can be assimilated as a set of autonomous ordinary differential equations, therefore, many numeric methods can be used to solve this problem. However, LF methods often need to compute one or more Jacobian matrix inversions in each iteration. Owing to this fact, these methods might not be computationally efficient. In this study, the authors propose combined Runge–Kutta Broyden's LF (RK4B) method in order to reduce the required Jacobian matrix inversion to only one in the first iteration. In this proposed method, Broyden's approach is employed in fourth-order Runge–Kutta method. In addition, two modifications of the proposed method are presented to reduce the number of iterations and improve the computational performance. The proposed method and the two modifications are validated using several well- and ill-conditioned cases. Results show that the combined approach has better computational performance than the classical multistage numeric methods, besides it preserves the robustness features of fourth-order Runge–Kutta method.
Development of different load flow methods for solving large-scale ill-conditioned systems
(Wiley, 2018-12) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
A new approach to sizing the photovoltaic generator in self-consumption systems based on cost–competitiveness, maximizing direct self-consumption
(Elsevier, 2019-01) López-Talavera , Diego; Muñoz-Rodríguez , Francisco José; Jiménez-Castillo, Gabino; Rus-Casas, Catalina
Applications for sizing Photovoltaic (PV) self-consumption systems have been studied over recent years in order to achieve either an optimization of the cost of energy, the investment cost or any economic profitability criteria. However, PV self-consumption systems at the residential or small business level can be designed with the aims of reducing the electricity consumption from the conventional local grid and achieving competitiveness with grid electricity prices. These criteria will provide not only greater environmental benefits, security and independence of the grid but it will make the cost of PV self-consumption electricity competitive with electricity prices from the power grid. In this sense, this paper proposes a method to size the generator for a PV self-consumption system based on cost-competitiveness, maximizing direct self-consumption. The method will be applied for three different households located in the south of Spain using the household daily consumption and generation profiles for a single year. However, the method here illustrated can be applied to other countries. The results obtained suggest that residential direct PV self-consumption systems with an annual global irradiation at the optimal tilt angle higher than 1000 kWh/(m2·year) may be a feasible investment to future owners of these systems.
Developed Newton-Raphson based Predictor-Corrector load flow approach with high convergence rate
(Elsevier, 2019-02) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
In this paper, a new methodology called Newton-Raphson-Predictor-Corrector (NR-PC) is applied to solve the load-flow (LF) problem of well and ill-conditioned power systems. In the proposed LF method, the Predictor-Corrector mechanism is developed to achieve convergence rate of order 1 + sqrt(2) = 2.4 instead of 2 for the standard Newton Raphson (NR). The proposed NR-PC LF method is validated on different test systems; IEEE 30-bus, 57-bus, 118-bus and 300-bus systems as well-conditioned test cases, 13-bus and 20-bus systems as naturally ill-conditioned test systems, 1354-bus, 2869-bus and 9241-bus systems as realistic very large-scale test systems. The sensitivity of the proposed method with different R/X transmission line ratios and loading conditions is validated and compared with well-known methods. The simulation results show that the proposed LF method has better convergence characteristics and low computation time compared with benchmark methods.
Monitoring PWM signals in stand-alone photovoltaic systems
(Elsevier, 2019-02) Jiménez-Castillo, Gabino; Muñoz-Rodríguez, Francisco José; Rus-Casas , Catalina; Casa-Hernández, Jesús; Tina, Giuseppe Marco
The performance of stand-alone photovoltaic (SAPV) systems can be evaluated by monitoring them in the field using data acquisition systems (DASs). Most SAPV systems use battery charge controllers with pulse width modulation (PWM) to regulate the current into the battery. The PWM signals generated by battery charge controllers imply monitoring challenges due to the complexity of this type of signal. In this sense, the aim of this paper is to develop a new and simple monitoring technique for SAPV systems which can estimate the signals provided by a PWM battery charge controller, thus avoiding expensive DASs, simultaneous sampling and the huge amount of collected data. The estimation of PWM signal parameters, such as the duty factor (df) or high and low states, shows high accuracy, with the mean absolute percentage error lower than 1.4%, a mean relative error within 1.4%, and the coefficient of determination higher than 0.9. Furthermore, the proposed technique may easily be used for other electrical devices where PWM is employed.
Development of a Utility Model for the Measurement of Global Radiation in Photovoltaic Applications in the Internet of Things (IoT)
(MDPI, 2019-03-08) Rus-Casas, Catalina; Hontoria, Leocadio; Fernández-Carrasco, Juan Ignacio; Jiménez-Castillo, Gabino; Muñoz-Rodríguez, Francisco José
In order to develop future projects in the field of photovoltaic solar energy, it is essential to accurately know the potential solar resources. There are many methods to estimate the incident solar radiation in a certain place. However, most of them are very expensive or do not have the ideal characteristics for good monitoring of a particular photovoltaic installation. For these reasons, an electronic device connected to the internet of things (IoT) is presented in this paper which manages to measure global radiation in photovoltaic applications. The device developed has been patented in the Spanish Patent and Trademark Office. It presents some features that make it very suitable to measure photovoltaic installations with the advantage of being a low cost and very reliable device. The device has been tested to determine global horizontal irradiance obtaining a correlation coefficient R2 = 0.994.
Improvements in Performance Analysis of Photovoltaic Systems: Array Power Monitoring in Pulse Width Modulation Charge Controllers
(MDPI, 2019-05-09) Jiménez-Castillo, Gabino; Muñoz-Rodríguez, Francisco José; Rus-Casas, Catalina; Gómez-Vidal, Pedro
Various challenges should be considered when measuring photovoltaic array power and energy in pulse width modulation (PWM) charge controllers. These controllers are frequently used not only in stand-alone photovoltaic (SAPV) systems, but may also be found in photovoltaic (PV) self-consumption systems with battery storage connected to the electricity grid. An acceptable solution may be reached using expensive data acquisition systems (DASs), although this could be generally disproportionate to the relatively low cost of SAPV systems. Therefore, the aim of this paper is to develop new and e ective monitoring techniques which will provide the PV array direct current (DC), output power (PA,dc), and PV array DC output energy (EA), thus avoiding the use of sophisticated DASs and providing high accuracy for the calculated parameters. Only transducers and electronic circuits that provide the average and true rms values of the PWM signals are needed. The estimation of these parameters through the aforementioned techniques showed high accuracy for both series and shunt PWM battery charge controllers. Normalized root mean square error (NRMSE) was lower than 2.4%, normalized mean bias error (NMBE) was between 􀀀1.5% and 1.1%, and mean absolute percentage error (MAPE) was within 1.6%.
A Robust Power Flow Algorithm Based on Bulirsch–Stoer Method
(IEEE, 2019-07) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
In this paper, we address the load-flow (LF) problem of very large scale systems. These types of systems show a very narrow region of attraction, and most of LF solvers tend to fail when a flat initial guess point is used. On the other hand, the solution of these systems frequently involves very large matrices and vectors. Consequently, a robust LF method must be used to find the correct solution of these systems. This paper proposes a robust and efficient LF solver based on the Bulirsch-Stoer algorithm. Moreover, a simple modification is proposed in order to improve its computational performance. The proposed methods are tested using various very large scale systems (i.e., more than 3000 buses) and compared with several standard and robust LF techniques. The obtained results show that the proposed methods are more suitable for solving the LF problem of very large scale systems.
Robust and efficient approach based on Richardson extrapolation for solving badly initialised/ill-conditioned power-flow problems
(Wiley, 2019-08) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
In this study, the authors focus on solving the power-flow (PF) problems of badly initialised/ill-conditioned power systems, where the solution of these systems is a challenge for most of state-of-the-art PF techniques. This challenge is increased in case of large and very large-scale power systems which have a huge number of variables. Consequently, the PF techniques used should have a high degree of efficiency in order to handle the large vectors and matrix computations. In this study, a novel PF approach based on the Richardson extrapolation is proposed to solve these systems. The proposed approach is validated using various badly initialised/ill-conditioned systems, comparing its performance with several well known PF techniques. The obtained results prove that the proposed approach is robust and efficient enough to properly manage the badly initialised/ill-conditioned systems even if they consist of a huge number of buses, whereas the other PF techniques face different convergence difficulties.
Comparison of various robust and efficient load-flow techniques based on Runge–Kutta formulas
(Elsevier, 2019-09) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
Based on Continuous Newton’s method, any well-assessed numerical scheme can be adapted for solving the Load-Flow (LF) problem. So far, LF techniques based on 4th order Runge–Kutta formula (RK4) and Adams–Bashfort’s methods (AB) have been proposed. However, there is a huge variety of numerical methods whose adequacy for solving the LF problem has not been explored yet. This paper tries to fill this gap by proposing several LF solvers based on Runge–Kutta (RK) formulas. Thus, several LF techniques based on Midpoint (MP), 3rd order Heun (H3), Simpson 3/8 (S3/8) and an accelerated 3rd order Runge–Kutta (ARK3) formulas are proposed. The performance of the proposed LF techniques is assessed using several medium and large-scale ill-conditioned power systems. The proposed techniques are compared with RK4, AB and other robust LF methods. In addition, their scalability and influence of the loading level are analyzed. The obtained results prove that the proposed LF techniques are faster than RK4 and robust enough to successfully tackle medium and large-scale ill-conditioned power systems. As main conclusion, it is proved that lower order methods might be as robust as higher order ones but more efficient. Therefore, its usage with respect higher order methods (e.g. 4th order ones), should be frequently preferable.
Several robust and efficient load flow techniques based on combined approach for ill-conditioned power systems
(Elsevier, 2019-09) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
This paper addresses the load flow (LF) problem of medium, large and very large-scale ill-conditioned power systems using several proposed techniques based on a combined approach. The proposed approach uses a novel combination among homotopic functions, numerical methods and the Newton’s technique for efficiently solving ill-conditioned systems. Using the proposed approach, any numerical method can be adapted to develop efficient and robust LF techniques. In this work, two novel LF techniques based on this combined approach using Forward-Euler formula and Ralston method are proposed. The proposed techniques are tested on several medium and large-scale ill-conditioned systems, comparing their performance with other well-known LF methods. Results show that the proposed LF techniques are robust and efficient enough to address the issues related with medium and large-scale ill-conditioned systems and they are not significantly affected by the initial guess considered.
An Effective Load-Flow Approach Based on Gauss-Newton Formulation
(Elsevier, 2019-12) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
Despite that most of power systems can be categorized as well-conditioned, ill-conditioned cases are becoming more frequent. Consequently, developing new robust LF techniques is necessary to efficiently solve these cases. In this paper, an effective load-flow (LF) approach based on Gauss-Newton’s formulation is proposed. Moreover, efficient strategies for exploring the unsolvable region and calculating the solution space boundary are developed. The proposed LF approach is comprehensively validated using a wide variety of ill-conditioned systems in loadbase conditions, near of the maximum loadability points and considering generator’ reactive limits. The studied systems range from 1888-bus to 70000-bus. The results prove the efficiency and superiority of proposed approach over other well-known LF methods.
A Three-Stage Algorithm Based on a Semi-Implicit Approach for Solving the Power-Flow in Realistic Large-Scale ill-Conditioned Systems
(IEEE, 2020) Tostado-Véliz, Marcos; Kamel, Salah; Alquthami, Thamer; Jurado-Melguizo, Francisco
Solving the Power-Flow in realistic large-scale ill-conditioned systems supposes a challenging task for most of available solution methodologies. This paper tackles this issue by developing a novel efficient and robust Power-Flow method. It is mainly based on a Semi-Implicit approach but incorporates other numerical arrangements for enhancing its features. The resulting three-stage algorithm is validated using several realistic ill-conditioned systems ranging from 3012 to 70000-buses. Results show that the developed methodology constitutes an efficient and robust Power-Flow solution technique, outperforming the results obtained with other available approaches.
Promising Framework Based on Multistep Continuous Newton Scheme for Developing Robust PF Methods
(Wiley, 2020-01) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
Solving power-flow (PF) problem of ill-conditioned systems is still a challenge in realistic power systems due to most of available techniques are quite inefficient. This study aims to address this issue by introducing a novel PF solution paradigm. It basically reformulates the traditional continuous Newton's method in a multistep scheme, so that, the variables are progressively refined each step using different numerical arrangements. The developed solution paradigm envisages a novel family of PF techniques. For the sake of exemplify, two novel methods based on the introduced solution paradigm are developed. They are tested in several large-scale realistic ill-conditioned systems under different stressing and demanding conditions. Up to eight well known PF solution techniques are considered for comparison. Results shown that the introduced solution paradigm constitutes a promising framework for developing robust and efficient PF methods, which may be widespread used in industry applications.
Development of a Prototype for Monitoring Photovoltaic Self-Consumption Systems
(MDPI, 2020-01-01) Rus-Casas, Catalina; Jiménez-Castillo, Gabino; Aguilar-Peña, Juan Domingo; Fernández-Carrasco, Juan Ignacio; Muñoz-Rodríguez, Francisco José
Currently, the increasing energy consumption around the world and the environmental impact resulting from the use of fossil fuel-based energy have promoted the use of renewable energy sources such as photovoltaic solar energy. The main characteristic of this type of energy is its unpredictability, as it depends on meteorological conditions. In this sense, monitoring the power generation of photovoltaic systems (PVS) in order to analyze their performance is becoming crucial. The purpose of this paper is to design a monitoring system for a residential photovoltaic self-consumption system which employs an Internet of Things (IoT) platform to estimate the photovoltaic power generation according to solar radiation and temperature. The architecture of the developed prototype will be described and the benefits of providing the use of IoT for monitoring will be highlighted, since all data collected by the data acquisition system (DAS) may be stored in the Cloud. The comparison of the results with those of other monitoring systems was very positive, with an uncertainty that complies with the IEC61724 standard.
Impacts of Array Orientation and Tilt Angles for Photovoltaic Self-Sufficiency and Self-Consumption Indices in Olive Mills in Spain
(MDPI, 2020-02-18) Jiménez-Castillo, Gabino; Muñoz-Rodríguez, Francisco José; Martinez-Calahorro, Antonio Javier; Tina, Giuseppe Marco; Rus-Casas, Catalina
Olive mills are extensive in the Mediterranean Basin, and Spain constitutes approximately 45% of global production. The industrial sector faces a new energetic paradigm where distributed generation provided by small renewable energy sources may reduce the dependence from fossil energy sources as well as avoid energy distribution losses. Photovoltaic self-consumption systems can play an important role in confronting this challenge due to their modularity and their decreasing cost. Most of self-sufficiency energy studies are focused on building sector and discussions about the idiosyncrasy of industrial load profiles, and their matching capability with photovoltaic generation profiles can be scarcely found. This work analyzes the potential of photovoltaic self-consumption systems as a function of the array power, array tilt, and orientation angles to face the electric consumption in olive mills. Different recording intervals and reporting periods are considered. Results show that a self-sufficiency index of 40% may be achieved on olive harvest basis. Moreover, due to the load profile particularities, percentage error lower than 1.6% has been found when considering a recording interval of 60 min when matching the olive load consumption and photovoltaic generation profiles. Chosen array tilt and orientation angles may be key parameters to maximize the self-sufficiency index.
A powerful power-flow method based on Composite Newton-Cotes formula for ill-conditioned power systems
(Elsevier, 2020-03) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
This paper proposes a novel Power-Flow method based on Composite Newton-Cotes formula. The proposed method aims to be robust and efficient enough to properly manage ill-conditioned power systems. Self-adapted mechanisms for tuning the parameters of proposed PF method are provided. The proposed method is tested on several ill-conditioned systems ranging from 3012 to 27,318 buses at loadbase and heavy loading conditions. Moreover, its ability to handle the generators’ reactive limits is also tested. The obtained results prove that the proposed method is remarkably robust and more efficient than other well-known Power-Flow techniques.
A new approach based on economic profitability to sizing the photovoltaic generator in self-consumption systems without storage
(Elsevier, 2020-04) Jiménez-Castillo, Gabino; Muñoz-Rodriguez, Francisco José; Rus-Casas, Catalina; López-Talavera, Diego
A proper assessment of the cost-competitiveness and profitability of self-consumption systems is crucial to promoting the transition from grid-dependent to energy self-sufficient buildings. Most of the approaches found in the literature may not take into account economic parameters such as taxes, depreciation and the cost of financing, which have a significant effect on the economic profitability of an investment. Moreover, they only focus on discrete array powers and relatively high recording intervals when estimating the self-consumed energy. In order to manage the aforementioned challenges, a new method will be developed to size the PV generator in a PV self-consumption system which provides the NPV curve together with the self-consumption and self-sufficiency indices for a wide range of array powers which suits residential self-consumption systems. Two scenarios will be considered depending on whether the generated surplus electricity is wasted or it is remunerated from the grid operator. Results show that not only the chosen scenario but the electricity tariff may be key parameters when optimizing NPV. Furthermore, the impact of the recording interval may be significant when estimating NPV. Percentage errors of 11.4% and 33.6% may be reached when considering a recording interval of 15 and 60 min, respectively.
An Efficient Power-Flow Approach Based on Heun and King-Werner’s Methods for Solving Both Well and Ill-conditioned Cases
(Elsevier, 2020-07) Tostado-Véliz, Marcos; Kamel, Salah; Jurado-Melguizo, Francisco
Solving the Power-Flow in ill-conditioned cases is still challenging as most of the available robust methodologies are not efficient enough to be widespread used in industry applications. This paper addresses this issue by developing a novel approach suitable for both ill and well-conditioned power cases. Since the developed approach arises from the combination of the King-Werner and Heun’s methods, it is called Heun-King-Werner method. The developed approach naturally performs as a robust method in ill-conditioned cases and as a high order Newton-like method in well-conditioned systems, which makes it very suitable for solving both cases. The developed approach is tested using various realistic well and ill-conditioned cases under different demanding scenarios. Its performance is compared with other well-known Power-Flow methods. Results show that the developed approach is robust, reliable and computationally much more efficient than other well-known methods. In well-conditioned systems, it performs similar to the standard NR method but improving its convergence features in some cases. Based on the results, the developed approach may be widespread used in industry tools.

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