This submission includes three peer-reviewed (under review) papers from the researchers at North Carolina State University presenting different control-based techniques to maximize the efficiency and robustness of a tethered energy-harvesting kite. Below are the abstracts of each file included in the submission.

Naik ACC - Geometric Structural Control Co-Design.pdf Focusing on a marine hydrokinetic energy application, this paper presents a combined geometric, structural, and control co-design framework for optimizing the performance of energy-harvesting kites subject to structural constraints. While energy-harvesting kites can offer more than an order of magnitude more power per unit of mass than traditional fixed turbines, they represent complex flying devices that demand robust, efficient flight controllers and are presented with significant structural loads that are larger with more efficient flight.

Daniels IFAC - Optimal Cyclic Spooling Control.pdf This paper presents a control strategy for optimizing the the spooling speeds of tethered energy harvesting systems that generate energy through cyclic spooling motions which consist of high-tension spool-out and low-tension spool-in. Specifically, we fuse continuous-time optimal control tools, including Pontryagin?s Maximum Principle, with an iteration domain costate correction, to develop an optimal spooling controller for energy extraction. In this work, we focus our simulation results specifically on an ocean kite system where the goal is to optimize the spooling profile while remaining at a consistent operating depth and corresponding average tether length.

Reed IFAC - Kite Control in Turbulence.pdf This paper presents a hierarchical control framework for a kite-based MHK system that executes power-augmenting cross-current flight, along with simulation results based on a high-fidelity turbulent flow model that is representative of flow conditions in the Gulf Stream. The hierarchical controller is used to robustly regulate both the kite?s flight path and the intra-cycle spooling behavior, which is ultimately used to realize net positive energy production at a base station motor/generator system. Two configurations are examined in this paper: one in which the kite is suspended from a surface-mounted platform, and another in which the kite is deployed from the seabed.