This article discusses the design, implementation, and virtual commissioning of a digital twin (DT) for the TCP-100 parabolic trough collector (PTC) research facility located at the Plataforma Solar de Almería (PSA) experimental installation in Spain. For these tasks, we have selected the following technologies: SIMATIC S7 1500 PLCs (programmable logic controller) for an IEC 61131-3 controller implementation, Dymola for an object oriented Modelica implementation of the TCP-100 behaviour simulator, Message Queuing Telemetry Transport (MQTT) broker bridging with a Linux Mosquitto broker for communication between the controller and simulator, and WinCC Unified to create the Human Machine Interface (HMI) for the system operator.

This is an application paper that provides a simulator and a control algorithm for a thermal collection line in a parabolic trough collector for solar generation of electricity. The simulation is designed to match the TCP-100 facility of the Plataforma Solar de Almeria, a full-scale CIEMAT research center, in Spain. Of interest to the research community would be the reveal of control issues and a solution that includes two nonlinear algorithms, explanation of a simulator that can serve as a benchmark for control algorithm testing, and comprehensive issues that need to be included in evaluating control algorithms. Of interest to the practitioner community would be the use of simple nonlinear control techniques embedded in a traditional cascade structure to solve nonlinear and deadtime issues.The simulator includes nominal direct normal irradiance (DNI) that changes over the day; random variations in DNI, optical efficiency, inlet temperature, ambient losses, and flow friction factor; and error on all measurements (calibration and noise).

This study explores appropriate optimization algorithms to maximize power production and minimize temperature distribution in parallel collection lines in a parabolic trough solar collection process for energy generation. The objective is to minimize parasitic power losses from the oil circulation pump while maintaining discharge fluid in all loops at the set point temperature. Features of the objective function topography and how it changes during the day are revealed, and appropriate optimizers discussed. Results of four optimization algorithms are revealed: Generalized Reduced Gradient and Incremental Steepest Descent (both single trial solution, gradient based), Cyclic Heuristic (single trial solution, direct search) and Leapfrogging (multiplayer, direct search).

In this article, we present the physical foundations and the development of a Modelica library with components for modeling 1-D thermofluid systems. Modelica was selected because it is an object-oriented modeling language that facilitates the incremental design of the library. Modelica also allows the modeling of acausal components, where the input/output relation is defined by the boundary conditions under which models are simulated. We model single-substance systems that are macroscopically homogeneous, isotropic, and uncharged, which we call “simple systems.” To model the behavior of these systems, we assume the postulate of classical irreversible thermodynamics. For the graphical representation of complex systems, we utilize a modified bond graph symbology to enhance the readability of the diagrams. We also implement the equations for viscosity and thermal conductivity to complete the IAPWS-95 model of water, enabling its use as a fluid in the piping systems presented in our examples.

This paper presents a Digital Twin analysis of a solar parabolic trough collector (PTC) plant, focusing on its integration into electrical distribution networks within the framework of Concentrated Solar Power (CSP). As renewable energy integration becomes increasingly vital, innovative methods are necessary to optimize network planning and enhance hosting capacity. This study, centered on the TCP-100 facility of Plataforma Solar de Almeria (CIEMAT), utilizes advanced modeling, simulation techniques, and real-time data analytics. The DT framework allows for a comprehensive assessment of the plant's performance under various conditions, identifying optimal operating parameters and addressing CSP-specific integration challenges. By exploring the interaction between the concentrated solar plants and the electrical distribution network challenges, the research aims to maximize power utilization efficiency while ensuring grid stability. Key contributions include the development of a specialized test tool for CSP integration, validated through real-world application within Turkey's GDZ network.

In this paper, a fault detection scheme is developed, based on a simplified model of a Parabolic Trough Collector that uses water as a heat transfer fluid. The model assumes some simplifications that allow the construction of a Luenberger-type observer-based residual, so that it provides information about the absolute thermal losses to the environment. A specificity/sensitivity analysis allows us to define two thresholds for the absolute value of the residual: in a faultless regime, it remains below the first threshold, so that if it is surpassed, a fault is detected. When a fault occurs, the second threshold is necessarily surpassed, so if the residual remains below this second threshold, we know that the system remains in a faultless regime. Simulations with different fault sizes illustrate the specificity and sensitivity of the detection scheme.

This paper focuses on the utilization of dynamic simulation models in the planning of experiments for control development. A set of models based on the first principles for system level simulation of the complete new TCP-100 research facility at Plataforma Solar de Almeria (CIEMAT) was planned for the development of control solutions for this new research facility which replaced the 32-year-old ACUREX facility. Many advances in Automatic Control have been reached by using the ACUREX field. Simulation experiments with the parabolic trough (PTC) field would require more tuning and adaptive parts before getting the required experimental data for typical operating conditions. The analysis operates for all state variables, which are temperatures, and input variables, which include solar radiation, ambient temperature and several setpoints. The nonlinear scaling approach keeps the algorithms unchanged by focusing on the meanings of the measured variables. The scaling functions are variable specific. For the irradiation, the functions do not change which means that also the indicator of the cloudiness remains the same. The algorithms are not changed and the data analysis is for a limited set of measurements and subsystems. The simulation experiments need to be first focused on the loops and modules of the solar field and the full model need to be extended before going to the full simulation tests and the test campaigns with the new facility. Copyright (C) 2024 The Authors. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/)

The efficiency of the solar plants is conditioned by the control strategies applied in their operation. In this paper, an application of a Model Predictive Controller based on nonlinear models of the TCP-100 parabolic trough collector solar plant is presented as one example of the advanced control techniques that can contribute to enhance the efficiency of this type of plants. Both types of nonlinear models of the TCP-100 facility are applied for this application: lumped and distributed parameter ones. The objective of the proposed control strategy is to face a problem that arises in current commercial solar trough plants, with hundreds of loops, where in practice each of those loops get a different outlet temperature of the heat transfer fluid. These temperature differences might cause inefficiency in the operation and/or irreversible damages by overheating, if not properly controlled. The presented control strategy computes the set-points of the control valves of each of the loops to achieve a good thermal balance of the solar plant. The proposed strategy implements also a heuristic based algorithm when strong transients are affecting the field. The simulation results show that the application of the proposed control technique balances the outlet temperatures of the loops, protecting the TCP-100 facility from damages and increasing its efficiency in the operation.

In this paper, we present the physical foundations and the development of the thermodynamic part of a Modelica library with the fundamental components for modeling thermofluid systems. We have chosen Modelica because it is an object-oriented modeling language that allows an elegant design of the library, with a top-down conception that starts from very general components where we model the thermodynamic properties common to all simple substances and descend by inheritance to model the properties of each particular substance. To model the behavior of each component, we have used: classical thermodynamics to define the equilibrium states, the local equilibrium hypothesis of Classical Irreversible Thermodynamics to model the changes of state, and the port-Hamiltonian approach to obtain the equations of the system dynamics. With this formulation, we implement the thermodynamic behavior of ideal gases (including monatomic gases as a particular case), the 2073 substances defined for the CEA (Chemical Equilibrium with Applications) NASA Glenn computer program, the IAPWS Formulation 1995 for the Thermodynamic Properties of Water Substance for General and Scientific Use, and the Syltherm 800 HTF (Heat Transfer Fluid). We also define graphical symbols for each library component that facilitate modeling complex systems with simple drag-and-drop manipulations, component connection, and parameter selection. These symbols are a slightly modified version of those used in bond graphs to facilitate their reading and the representation of the structure of complex systems. We also show the modeling, simulation, and comparison for accuracy, performance, and scalability of some thermodynamic systems implemented with the Modelica Standard Library (MSL) and the proposed library.

Advanced control strategies can play an important role in improving the efficiency of solar plants. In particular, linear model predictive control strategies have been applied successfully when controlling solar trough plants. However, if the control algorithm uses a linear model associated only with one operating point, when the plant is working far from the design conditions, the performance of the controller may deteriorate. In this paper, a fuzzy model-based nonlinear model predictive controller is applied to the new TCP-100 solar facility. The control strategy uses a fuzzy model of the plant for predicting the future evolution of the outlet temperature. This approach reduces the computational time of the nonlinear model predictive control strategy and allows to solve it much faster than using the full nonlinear model.

The TCP-100 parabolic trough collectors (PTC) research facility at Plataforma Solar de Almeria (CIEMAT) has been specially designed for the development of research activities in Automatic Control of PTC solar thermal power plants. The development of advanced control techniques for this kind of facilities requires dynamic models that should be successfully used in advanced controllers. An important part of these models is the thermal losses submodel, that traditionally has been considered as an experimental steady state correlation. In this paper, a work in progress about a first principles based model of the losses to the environment of a parabolic trough collector is presented, based on the physical phenomena inside any parabolic trough collector during the operation of the TCP-100 solar field. The implementation of the model in the Modelica language has been done prioritizing the use of the Modelica Standard Library classes. Some simulations results of this model with theoretical parameters values under typical operating conditions of the TCP-100 plant are presented, showing higher losses to the environment when compared with the information provided by the TCP-100 manufacturer.

The TCP-100 parabolic trough collectors research facility at Plataforma Solar de Almería (CIEMAT) has replaced the 32 years old ACUREX research plant, widely used in Automatic Control research. The new TCP-100 structure poses new challenges in the design of more sophisticated operation modes. This paper presents a hybrid first principles system level model of the TCP-100 facility, which is based on two connected parts: a previously published non-linear continuous dynamic model, and a discrete part modelling the behaviour of an operator. This model is able to cover the different operation modes of the plant and proves its applicability for operation training activities. The discrete part of the model characterizes the operation procedure using both the StateGraph formalism in the Modelica object oriented modelling language, and the Dymola tool. We illustrate the validity of our hybrid model by simulating two different operation procedures applied to the TCP-100 plant model in a typical operation day in which the system passes through several operating modes.

In this article we present the implementation in Modelica language of a library with the fundamental components for modeling a wide variety of multiphysics systems. Modelica is an object-oriented modeling language, which allows to make a simple, systematic and elegant design of the library. The mechanisms of inheritance and composition of Modelica facilitate the modeling and reuse of components in different domains of Physics. To model the behavior of each component in a systematic framework we have used the theory of port-Hamiltonian systems, formulated mainly by means of differential geometry. The port-Hamiltonian approach allows a methodical definition of complex systems by connecting simple systems that exchange energy through connection ports. To graphically represent the components of a system and their connections, we have employed slightly modified bond graphs symbols for easier reading. The general and systematic applicability of the library is illustrated via two examples framed in different domains of Physics: the mechanical Sun-Earth-Moon system where we perform an analysis of errors that justifies the employed system of units, and the electrical nonlinear Chua circuit, modeled by composition of port-Hamiltonian subsystems. Both derived models have been built and simulated based on the more general models of mechanical and electrical systems, which are also part of the library developed with the port-Hamiltonian approach.

The aim of this paper is to present a new bidirectional DC-DC linearized converter model for use in power demand and recovery units mainly used in Lightweight Electric Vehicle applications. The model significantly reduces the simulation time of the experiments performed, with up to a 4450-fold decrease in simulation times with respect to the original switched DC-DC topology. The study begins with a literature review of available switched converters, after which the presented topology is selected. The object-oriented modeling language Modelica ® is used to implement the converter in the Dymola ® modeling environment. Components and base classes from the Modelica Standard Library and VehicleInterfaces library are mainly used for better interoperability. Because of the intensive use of converters in the whole vehicle and the time consumed by the converter simulations due to high frequency commutation, a linearized DC-DC converter model is proposed. Comparison tests are performed between the reference switched models and the proposed linearized models in Dymola ® tool to validate the linearized model behaviour. Nearly identical responses are obtained for both models, while simulation times are reduced as much as 1/4450 for the linearized converter. Furthermore, validation tests are carried out between the proposed linearized model in Dymola ® and a reference switched model in LTspice ® specific purpose simulation package for switched electronic circuits. Excellent agreement in the responses of both models is observed.

En este artículo se propone un modelo dinámico de batería que permite simular el comportamiento de distintos tipos de baterías para su aplicación en vehículos eléctricos urbanos ligeros. El modelo es fácilmente parametrizable a partir de las curvas de descarga experimentales del equipo real y se ajusta adecuadamente al comportamiento particular de la curva de carga/descarga de las baterías de Litio-Ferrofosfato (LiFePo4). Se han utilizado los datos obtenidos sobre una instalación experimental para la calibración del modelo propuesto y se presentan resultados de la validación del mismo. El modelo se ha implementado en el lenguaje de modelado orientado a objetos Modelica reutilizando clases de su librería estándar Modelica Standard Library. La calibración y validación se ha realizado con la herramienta de modelado Dymola.

There are two main drawbacks when operating solar energy systems: a) the resulting energy costs are not yet competitive and b) solar energy is not always available when needed. In order to improve the overall solar plants efficiency, advances control techniques play an important role. In order to develop efficient and robust control techniques, the use of accurate mathematical models is crucial. In this paper, the mathematical modeling of the new TCP100 parabolic trough collector (PTC) research facility at the Plataforma Solar de Almería is presented. Some simulations are shown to demonstrate the adequate behavior of the model compared to the facility design conditions.

This paper presents a set of first principles based models for system level simulation of the complete new TCP-100 research facility at Plataforma Solar de Almería (CIEMAT). This new research facility replaced the 32 years old ACUREX facility with which so many advances in Automatic Control were reached by the research community The presented models will be validated with experimental data and the presented simulations are based in the parameter selection from providers’ data sheets and the engineering design project. Results of several simulation experiments for a typical operation day are presented in which the system is operated passing through different operating modes.

In this paper a set of mathematical conditions on heliostat models is presented.Its purpose is to guarantee a deterministic computation of the heliostat setpoints in azimuth (β ) and elevation (α).In Central Receiver (CR) Concentrating Solar Power (CSP) plants, thousands of heliostats are continuously operated, and the updating of their setpoints is required frequently.For this reason, the fulfillment of some mathematical conditions of the mentioned type is important.In a simplified approach, during the operation, each heliostat reflects in its mirror a ray from the sun that impacts on a given aiming point P.This aiming point is assumed to be higher than the heliostat position, in the tower receiver.If v is the incident solar vector, x is the orthogonal vector of the heliostat reflective plane and f (x) is the center of the heliostat mirror, then a system of equations with unknown x is arisen.Imposing certain conditions on f , we can ensure the existence and uniqueness of solution of this system, and provide a sequence converging to such solution.Furthermore, we offer a numerical method for approximating the solution in a deterministic form, which can be computed with the requirements of hard real time systems.