A Multivariable Controller for the Start-up Procedure of a Solar Membrane Distillation Facility

Abstract

This paper presents a multivariable TITO (two inputs two ouputs) controller aimed to improve the start-up procedure of a Solar Membrane Distillation (SMD) facility, located at Plataforma Solar de Almería (PSA). The control structure includes PID controllers and decouplers, as well as a reference governor based on a real time optimizer. The filtered Smith Predictor (SP) control structure has been used for controlling one of the output variables, whereas a cascade control scheme is employed to control the other one. The proposed approach has been tested in simulation on a nonlinear model of the SMD facility, showing promising results.

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

“…However, the problem related to the stratification of the tank was not considered. A second step towards the improvement of the start-up procedure was presented in Gil et al (2018a) anteeing that the temperature of the fluid flowing to the tank was higher than the one at the top of the tank. On the other hand, the multivariable controller was tasked with tracking the setpoints computed by the reference governor by acting on both pump 1 and valve 1.…”

“…In the present work, the idea for improving the start-up procedure is the same that the one presented in Gil et al (2018a), which consists on using valve 1 as a control variable for heating the tank faster. However, the control structure has been considerably improved by using a hierarchical control system composed of two layers: i) an upper layer based on a predictive controller, and ii) a regulatory layer based on PID controllers.…”

“…In the upper layer, the predictive controller uses the nonlinear model of the system presented in Section 3 for making the predictions and calculating the setpoints for the regulatory layer. In this way, a prediction horizon and a nonlinear model are considered in the control procedure, allowing to calculate the setpoints more accurately than in the approach proposed in Gil et al (2018a), in which a steady-state model and static values are used for calculating the references. The regulatory layer comprises a cascade control scheme for controlling the outlet solar field temperature by acting on pump 1, and a Filtered Smith Predictor (FSP) structure for controlling the inlet temperature of the solar field by using valve 1.…”

“…The regulatory layer comprises a cascade control scheme for controlling the outlet solar field temperature by acting on pump 1, and a Filtered Smith Predictor (FSP) structure for controlling the inlet temperature of the solar field by using valve 1. These two control systems were also used in the two loops of the multivariable controller proposed in Gil et al (2018a). However, in this work, the multivariable approach has not been considered due to the low interaction between the variables involved in the process, as was analyzed in Gil et al (2018a).…”

“…These two control systems were also used in the two loops of the multivariable controller proposed in Gil et al (2018a). However, in this work, the multivariable approach has not been considered due to the low interaction between the variables involved in the process, as was analyzed in Gil et al (2018a). Moreover, the FSP controller has been improved by adding the nonlinear model of valve 1.…”