Hierarchical control for the start-up procedure of solar thermal fields with direct storage

Abstract

Thermal energy storage tanks are habitually combined with solar thermal fields to improve the dispatchability of these facilities. From the dynamical point of view, the start-up phase is relevant since if the storage device is unloaded in terms of energy or widely stratified, the transitory regime can take long time until reaching the operating point. In this paper, an optimal real-time procedure based on a hierarchical controller for improving the start-up phase is proposed. The hierarchical controller is composed of two layers based on a Model Predictive Control (MPC) technique and Proportional Integer Derivative (PID) controllers. Real experimental tests were performed in a pilot facility located at Plataforma Solar de Almería (Almería, Spain). In addition, a comparison in simulation with the typical manual procedure and with two techniques proposed previously in the literature for the same plant is provided. The results demonstrate the benefits obtained by using the proposed method; since it reduces the start-up phase in 34 [min] in comparison with the manual operation, and in 26 and 6 [min] with respect to the two previous techniques.

An economic D-RTO for thermal solar plant: analysis and simulations based on a feedback linearization control case

“…Since the purpose of this work is to analyze the proposed D-RTO algorithm, it is important to emphasize that these simulated scenarios are defined to provide a broader range of conditions and, thereby, expand the limits to evaluate the performance of the dynamic optimization strategy, although, in real process the difference in inlet and outlet temperature is maintained between 5 o C and 20 o C to avoid stress in CPC materials (Roca et al, 2008;González et al, 2014).…”

“…The AQUASOL can be operated on three modes: (i) solar, in which the required input temperature of the MED is reached using only the solar field in good weather conditions; (ii) fossil, when MED works supplied by the gas boiler coupled to the DEAHP due to low irradiance or during the night; and (iii) hybrid, in which there is a combination between the previous modes avoiding the gas boiler as much as possible. The whole water desalination process is detailed in the researches of Roca et al (2008) and González et al (2014). In this work, it is considered the AQUASOL operating on the solar mode, as shown in Figure 1.…”

“…Equation 6 can be separated in two terms: the right one refers to the cost associated to electricity consumption caused by the solar field pump, in which E ec is calculated in euros, given c On the left is calculated the benefits, wherein c 1 = 8.171 • e −10 e/J represents the approximated value for each joule required by the MED plant, considering a minimum operating temperature T omin to produce fresh water. The heated water price is estimated by the total distilled water production in simulations performed by González et al (2014). To simplify implementation, d v is considered only on benefit term, since it presents a higher magnitude.…”

“…Also, many works have been dedicated to the development of mathematical models and simulation of solar thermal processes (Americano-daCosta et al, 2020). Although there are important studies focused on achieving optimal operation of solar thermal plants, for instance Gallego et al (2013); Vega and Cuevas (2018); Gil et al (2020), there is still motivation to explore dynamic optimization in these processes, especially when economic aspects are considered. In fact, according to industrial experts, the optimization layer can increase a profitability of a process by 7% to 10%.…”

Uso del paradigma Take-Home Labs para la enseñanza del control automático en estudios de ingeniería

“…Figura 6. Esquema control self-tuning Porúltimo, los alumnos deben implementar en TCLab estrategias de control predictivo [16] y control jerárquico [9]. Para ello, de los diferentes algoritmos de control predictivo estudiados en la asignatura, lineales y no lineales, deben utilizar alguno para controlar la temperatura del sistema en torno a uno o varios puntos de operación.…”