Position Control of Solar Powered Aerostat for Reliable Power Generation in the Presence of Clouds

This paper presents single tethered and bi-tethered position control of a solar-powered aerostat. The objective is to station the aerostat at a desired position anywhere into and on a hemisphere of an allocated radius with constraints applied on tether lengths and controller gains. Optimization is performed to find an optimal set of PID controller gains in order to minimize the total error over the entire trajectory. Two schemes for integral error calculation are proposed in this work. The first scheme implements historical values of the error resulting in adding an unnecessary bias to the output. This is overcome by the use of an error history over a finite horizon when calculating the integral error. Improved performance of the controller with faster convergence for position tracking is achieved by the implementation of the second scheme. In the first scheme, a settling time of approximately 72 s is achieved which is improved to approximately 40 s with the implementation of the second scheme. The conditions for position change of the aerostat are discussed. The results depict a three- dimensional space trajectory of the solar-powered aerostat being relocated to a cloudless new position for reliable solar power generation.