In this paper, an advanced control algorithm is presented for avoiding fluid overheating when operating solar thermal plants. The control algorithm manipulates the fluid rate to maintain the field output temperature in the desired reference, and defocus the solar collectors when the temperature reaches a maximum limit. Several simulation scenarios are considered for the test of the proposed controller using a lumped parameters model of the solar collectors that has been validated in real plants. A discussion is carried out aiming at analyzing the behavior of the controlled solar plant, and comparing the characteristics and performance of the proposed algorithms. (C) 2019 Elsevier Ltd. All rights reserved.