Solar energy is used worldwide to alleviate the daily increasing demands for electric power. Photovoltaic (PV) cells, which are used to convert solar energy into electricity, can be represented as equivalent circuit models, in which a series of electrical parameters must be identified in order to determine their operating characteristics under different test conditions. Intelligent approaches, like those based in population-based optimization algorithms like Particle Swarm Optimization (PSO), Genetic Algorithms (GAs), and Simulated Annealing (SA), have been demonstrated to be powerful methods for the accurate identification of such parameters. Recently, chaos theory have been highlighted as a promising alternative to increase the performance of such approaches; as a result, several chaos-based optimization methods have been devised to solve many different and complex engineering problems. In this paper, the Chaotic Gravitational Search Algorithm (CGSA) is proposed to solve the problem of accurate PV cell parameter estimation. To prove the feasibility of the proposed approach, a series of comparative experiments against other similar parameters extraction methods were performed. As shown by our experimental results, our proposed approach outperforms all other methods compared in this work, and proves to be an excellent alternative to tackle the challenging problem of solar cell parameters identification.

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Abstract:Recently, many researchers have proved that the electrification of the transport sector is a key for reducing both the emissions of green-house pollutants and the dependence on oil for transportation. As a result, Plug-in Hybrid Electric Vehicles (or PHEVs) are receiving never before seen increased attention. Consequently, large-scale penetration of PHEVs into the market is expected to take place in the near future, however, an unattended increase in the PHEVs needs may cause several technical problems which could potentially compromise the stability of power systems. As a result of the growing necessity for addressing such issues, topics related to the optimization of PHEVs' charging infrastructures have captured the attention of many researchers. Related to this, several state-of-the-art swarm optimization methods (such as the well-known Particle Swarm Optimization (PSO) or the recently proposed Gravitational Search Algorithm (GSA) approach) have been successfully applied in the optimization of the average State of Charge (SoC), which represents one of the most important performance indicators in the context of PHEVs' intelligent power allocation. Many of these swarm optimization methods, however, are known to be subject to several critical flaws, including premature convergence and a lack of balance between the exploration and exploitation of solutions. Such problems are usually related to the evolutionary operators employed by each of the methods on the exploration and exploitation of new solutions. In this paper, the recently proposed States of Matter Search (SMS) swarm optimization method is proposed for maximizing the average State of Charge of PHEVs within a charging station. In our experiments, several different scenarios consisting on different numbers of PHEVs were considered. To test the feasibility of the proposed approach, comparative experiments were performed against other popular PHEVs' State of Charge maximization approaches based on swarm optimization methods. The results obtained on our experimental setup show that the proposed SMS-based SoC maximization approach has an outstanding performance in comparison to that of the other compared methods, and as such, proves to be superior for tackling the challenging problem of PHEVs' smart charging.

Recently, the use of renewable energy has attracted the interest of several scientific communities due to the environmental consequences of fossil fuels. Many different technologies have been proposed for the exploitation of clean energies. One of most used is the solar cells considering their unlimited source power characteristics. The estimation of solar cell parameters represents a critical task since its efficiency directly depends on their operative values. However, the determination of such parameters presents several difficulties because of the non-linearity and the multimodal properties from the estimation process. The problem of solar cell parameter estimation has been widely faced through Evolutionary Computation (EC) techniques. Essentially, these methods have produced better results than those obtained by classical methods regarding accuracy and robustness. Each EC algorithm has been designed to fulfill the conditions of specific problems since no one approach can optimize all problems effectively. Under such circumstances, the performance of each EC approach must be correctly assessed considering the application context. Several proposals of EC methods to estimate the parameters of solar cells have been reported in the literature. However, most of them report only a single EC technique considering a minimal number of solar cell models. In this paper, a comparative study of EC techniques used for solar cells parameter estimation is proposed. In the study, the most popular EC approaches currently in use are considered, evaluating their performance over the complete set of solar cell models.

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