Nonlinear controllers for solar thermal plants: A comparative study

• Two nonlinear controllers are presented to regulate the temperature of solar plants.
• Experimental and simulation tests are performed.
• The proposed controllers present better accuracy than a PI controller.
• NMPC algorithm shows prominent disturbance rejection capabilities.
• Distributed sliding mode control has better robustness properties.

Solar plants have nonlinear dynamics which must be taken into account when a control system is applied to them. The main purpose of the control systems is to maintain the outlet temperature in a desired reference value and, at the same time, attenuate the undesirable transients caused by the disturbances. Linear controllers, like PID ones, are not able to obtain good performance over the whole operation range of these kind of plants. To overcome these limitations two nonlinear controllers, a nonlinear model-based predictive controller and a distributed sliding mode controller, are applied to a solar plant in this work. The performance of these controllers is tested through experimental and simulation results, which show the tracking and disturbance rejection capabilities of the proposed controllers.