DEVELOPMENT OF CONTROL STRATEGIES FOR HELIOSTAT AIMING IN SOLAR POWER TOWER PLANTS

Abstract

In this work, two closed-loop controllers are proposed, which control the flux density distribution on the receiver of a solar power tower plant. The first controller, called Hot Cold Control, is based on the idea from GarcÍa-MartÍn et al. [1] and modified to work with the flux density measurement as input. Secondly, a novel control approach is presented, called Static Optimal Control, which is based upon the ant colony optimization algorithm. In a simulation, the controllers are tested under three test cases. The first two test cases evaluate the controllers capacity to compensate for disturbances like mirror errors and to react to overflux conditions. The last test case investigates the controller’s reaction to dynamic disturbances like clouds. The Static Optimal Control shows the most promising results. Under the influence of a mirror error it raises the relative power from 88.9 % to 92.2 %. This is close to the calculated maximum of 93.7 % and 1.67 % higher than the Hot Cold controller, which yields a relative power of 90.53 %. The overflux condition in test case 2 is eliminated after one control step by the Static Optimal Control and results in a relative power of 92.02 %. The Hot Cold control requires 61 steps and yields a relative power of 90.53 %. Only the Static Optimal Control is tested for test case 3, where it increases the power while the heliostat field is partly shaded and compensates overflux conditions after the cloud passes. Finally, the Static Optimal Control is tested on the solar tower in Jülich. Here, the controller also shows promising results. However, for a commercial plant the elimination of an overflux condition is not fast enough. To guarantee a robust control behavior, further testing and development has to be done.