Sensor Fusion Observer Design and Experimental Validation for an Underwater Kite.

Underwater energy-harvesting kites possess the capacity, under appropriate control algorithms, to deliver more than an order of magnitude additional power per unit mass than stationary devices. However, in order to perform path-following control, it is essential to maintain accurate estimates of the kite's position and velocity. Obtaining these measurements is complicated by: (i) operation in GPS-denied environments, and (ii) tether curvature, which renders straight-line approximated, line angle sensor-based measurements inaccurate. In this paper, we present a nonlinear closed-loop observer that fuses line angle sensor and IMU measurements using a dynamic tether model to maintain an estimate of an underwater kite's states. The observer design has been experimentally validated on a 1/10-scale kite model, using a customized tow testing system deployed in the NC State Aquatic Center.