Control Co-design of a Hydrokinetic Turbine: A Comparative Study of Open-loop Optimal Control and Feedback Control

TL;DR

This paper compares open-loop optimal control and feedback control in the co-design of hydrokinetic turbines, showing feedback control offers robustness and simplicity despite slightly lower energy output.

Contribution

It introduces a CCD framework explicitly incorporating feedback controllers, demonstrating their advantages over traditional open-loop control in hydrokinetic turbine design.

Findings

Feedback control approximates OLOC trajectories.

Feedback control provides robustness against uncertainties.

Energy output is slightly lower with feedback control.

Abstract

Control co-design (CCD) explores physical and control design spaces simultaneously to optimize a system's performance. A commonly used CCD framework aims to achieve open-loop optimal control (OLOC) trajectory while optimizing the physical design variables subject to constraints on control and design parameters. In this study, in contrast with the conventional CCD methods based on OLOC schemes, we present a CCD formulation that explicitly considers a feedback controller. In the formulation, we consider two control laws based on proportional linear and quadratic state feedback, where the control gain is optimized. The simulation results show that the OLOC trajectory could be approximated by a feedback controller. While the total energy generated from the CCD with a feedback controller is slightly lower than that of the CCD with OLOC, it results in a much simpler control structure and more robust performance in the presence of uncertainties and disturbances, making it suitable for real-time control. The study in this paper investigates the performance of optimal hydrokinetic turbine design with a feedback controller in the presence of uncertainties and disturbances to demonstrate the benefits and highlight challenges associated with incorporating the feedback controller explicitly in the CCD stage.