Adaptive envelope control design for a Buoyant Airborne wind energy system

The focus of this paper is centered on the Buoyant Airborne Turbine (BAT) developed by Altaeros Energies. This system is part of a new class of wind energy system known as Airborne wind energy systems (AWES). To inform the reader, a brief review of the current control architecture for different types of AWES is presented. The paper then evaluates the control architecture for the Altaeros system and illustrates through a frequency domain analysis the impact that operating conditions will have on movement in roll, pitch and altitude. The primary contribution of this paper rests in the design of a multiloop novel adaptive low level PD controller that is developed from linearized models covering the full operating envelope. PD gains are adapted as a function of the system operating conditions and tuned as a function of the multi-loop bandwidth. As such it is shown that the control design varies with wind conditions and so facilitates the need for this adaptive approach. This work illustrates that a model free multiloop controller can be achieved without the need for extensive calibration parameters as in the classic LQR approach and demonstrates the merits of simplified PD tuning strategies when faced with complex multivariable problems.