Optimal control of solar collector fields based on linear quadratic controller with accessible disturbance*

This work proposes a Linear Quadratic Regulator with Feedforward action (LQR-FF) aiming to improve the performance of optimal controllers applied to control thermal Solar Collector Field (SCF) systems The proposed strategy advances over the linear quadratic controllers proposed in the literature since it accounts for disturbance compensation and process delays in a combined solution. For this purpose, an augmented state-space model directly considers the inputs and disturbances delays in the control design. Furthermore, the LQR-FF design embeds a robustness analysis of the actual model errors that arise from real scenarios in the control of solar collectors due to, namely, nonlinearities and model parameter uncertainty. The LQR-FF is compared to the Linear Quadratic Gaussian with Loop Transfer Recover (LQG/LTR) in a trustworthy simulated scenario using validated models of the solar thermal plant located in CIESOL (University of Almeria, Spain). The results show that, by considering the system delays with no approximation and using the FF action in the optimal control law, the LQR-FF improves the control of SCF compared to the LQGILTR approach, reducing the reference tracking error by up to 18% in the tested scenarios, which can contribute to enhancing the solar thermal plant efficiency.