Null-Space-Excitation-Based Adaptive Control for an Overactuated Hexacopter Model

This paper proposes a novel adaptive control structure featured by large closed-loop bandwidth and satisfactory parameter estimation results. The proposed baseline control structure is consisted of a velocity controller, an angular rate controller, and a pseudo-inverse-method-based control allocation module. For multirotor systems with immobile propellers, this structure is able to provide commands of pseudo inputs without redundancy. These commands will then be allocated through control allocation matrix possessing necessary elements. By using noncascaded velocity controller and considering actuator dynamics, the bandwidth of whole controller is broadened and a chance of estimating control effectiveness together with bandwidths of actuators appears. The null space excitation method is developed in this paper for assisting in parameter estimation, which will inject excitation signals in null space of control allocation matrix and therefore will not influence allocation results. This method is able to enlarge data information evaluated by Fisher information matrix. Hence, estimating parameters with these excitation signals is faster and more accurate than estimations in common methods. Designed null-space-excitation-based adaptive controller is validated on a complex high-fidelity hexacopter model and shows satisfactory performance in terms of control and parameter estimation.