A nonlinear optimal control approach for the autonomous octorotor

Abstract

The article proposes a nonlinear optimal control approach for the model of the autonomous octorotor. This aerial drone has improved load transport capability due to being actuated by eight rotors. The dynamic model of the octorotor undergoes approximate linearization with the use of Taylor series expansion around a temporary operating point which is recomputed at each iteration of the control method. For the approximately linearized model an H‐infinity feedback controller is designed. The linearization procedure relies on the computation of the Jacobian matrices of the state‐space model of the octorotor. The proposed control method stands for the solution of the optimal control problem for the nonlinear and multivariable dynamics of this aerial drone, under model uncertainties, and external perturbations. For the computation of the controller's feedback gains an algebraic Riccati equation is solved at each time‐step of the control method. The new nonlinear optimal control approach achieves fast and accurate tracking for all state variables of the octorotor, under moderate variations of the control inputs. The stability properties of the control scheme are proven through Lyapunov analysis. It can be noted that: (1) the novelty/innovation of this research work is in presenting a novel and genuine nonlinear optimal control method for the octocopter's model, (2) the significance of the presented method is in achieving fast and accurate tracking of reference setpoints for the octocopter under moderate variations of the control inputs. By minimizing energy consumption by the actuators of the UAV its autonomy and operational capacity is improved, (3) the intellectual contribution of the article is in solving the nonlinear optimal control problem for the octocopter in an effective, yet computationally efficient manner.

An Innovative UAV with VTOL Capabilities

“… Safety Management: safety protections and failure mitigation policies are modelled in this sub-model. Resulting model can simulate different propulsion modes and the transition between them during a typical mission profile which is shown in Figure 3: proposed UAV can perform VTOL using only vertical propellers as a standard octocopter [47]. As the UAV reaches an assigned altitude, transition from VTOL to fixed wing mode and vice versa can be performed using transition methods proposed in literature [48].…”

“…Proposed UAV can be controlled as a standard octocopter [53]. As shown in figure 7, the total propulsion force Ttot (respect to a fixed frame) is the sum (11) of the contributions of the eight vertical propellers (T1-T8).…”

Nonlinear optimal control for a 4-DOF SCARA robotic manipulator

“…Comparing to past attempts for solving the H-infinity control problem for nonlinear dynamical systems, the article’s control approach is substantially different [37]. Preceding results on the use of H-infinity control to nonlinear dynamical systems were limited to the case of affine-in-the-input systems with drift-only dynamics and considered that the control inputs gain matrix is not dependent on the values of the system’s state vector.…”

“…In the present article, a nonlinear optimal control method is proposed for the nonlinear model of a 4-degrees of freedom (DOF) SCARA robot [36, 37]. The dynamic model of the 4-DOF SCARA robot undergoes first approximate linearization around a temporary operating point which is updated at each sampling instance.…”

“…The article has a meaningful contribution to the area of nonlinear control. One can point out the advantages of the nonlinear optimal control method against nonlinear model predictive control (NMPC) [37]. In NMPC, the stability properties of the control scheme remain unproven and the convergence of the iterative search for an optimum often depends on initialization and parameter values’ selection.…”