Marco M. Nicotra

Taut Cable Control of a Tethered UAV

This paper focuses on the design of a stabilizing control law for an aerial vehicle which is physically connected to a ground station by means of a tether cable. When the cable is taut, the resulting dynamic model is shown to be characterized by a new set of equilibria which untethered aircraft are unable to maintain in steady state. The control objective is to steer the UAV to a desired set-point while maintaining the cable taut at all times. This leads to a nonlinear control problem subject to constraints. A cascade control scheme is proposed and proven to asymptotically stabilize the overall system by means of ISS arguments. Constraint satisfaction is guaranteed using a modified thrust vector control coupled with a reference governor strategy. The effectiveness of the proposed control strategy is shown via numerical simulations.

Explicit Reference Governor for Constrained Nonlinear Systems

This technical note introduces a novel control law that dynamically modifies the reference of a pre-compensated nonlinear system to ensure the satisfaction of constraints. This is done by translating the state space constraints into an upper bound on the value of the Lyapunov function and by manipulating the velocity of the applied reference to enforce this bound. The main advantage of this approach is that it systematically provides a closed-form control law able to enforce constraints. The theory is introduced for general nonlinear systems subject to constraints and is then specialized to the large and highly relevant class of nonlinear systems admitting a Lyapunov function lower-bounded by a quadratic form and subject to linear constraints. Numerical simulations show the effectiveness of the proposed method.

Explicit reference governor for continuous time nonlinear systems subject to convex constraints

This paper introduces a novel control law that dynamically modifies the reference of a pre-compensated nonlinear system so as to ensure the satisfaction of convex constraints. This is done by translating the state space constraints into a constraint on the Lyapunov function which is then limited by modulating the velocity of the applied reference. The main advantage of this approach is that it systematically provides a closed-form expression of the control law. The theory is introduced for general nonlinear systems subject to convex constraints and is then specialized to the large and highly relevant class of nonlinear systems with a Lyapunov function that is lower-bounded by a quadratic form. Numerical and experimental validations are also provided.

Nonlinear control of an actuated tethered airfoil

This paper focuses on the control of an aerial vehicle composed of an aerodynamic profile linked to a ground station by means of a tether cable. The vehicle is sustained only by the wind flowing on the aerodynamic surface. The control objective is to steer the vehicle to a desired reference point while satisfying the constraint of having the cable taut at all times. In this paper, a nonlinear state feedback with a state dependent saturation is proposed which, using Lyapunov theory, is proven to ensure regional asymptotic stability. Moreover, it is proven that this law, thanks to a state dependent saturation, ensures constraints satisfaction. The effectiveness of the proposed control strategy is shown through simulations based on the experimental aerodynamic data of a real airfoil.

Nonlinear control of a tethered UAV: The taut cable case ☆

Abstract This paper focuses on the design of a stabilizing control law for an aerial vehicle physically connected to a ground station by means of a tether cable. By taking advantage of the tensile force acting along the taut cable, it is shown that the tethered UAV can maintain a non-zero attitude while hovering in a constant position. The control objective is to stabilize the desired configuration while simultaneously ensuring that the cable remains taut at all times. This leads to a nonlinear control problem subject to constraints. This paper provides a two-step solution. First, the system is stabilized using a cascade control scheme based on thrust vectoring. Then, constraint satisfaction is guaranteed using a novel Reference Governor scheme.

An Explicit Reference Governor for the robust constrained control of nonlinear systems

The Explicit Reference Governor is a simple and systematic approach that provides constraint handling capabilities to pre-stabilized nonlinear systems. The approach consists in translating state and input constraints into a constraint on the value of the Lyapunov function which is then enforced by suitably manipulating the derivative of the applied reference. This paper extends the Explicit Reference Governor approach by addressing its robustness in the presence of external disturbances and parametric uncertainties. Using ISS arguments, it will be shown that the robustness with respect to external disturbances can be ensured by simply restricting the domain of the applied reference. Parametric uncertainties can instead be accounted for using suitable bounds on the Lyapunov function. Numerical simulations show the effectiveness of the proposed method.

A robust explicit reference governor for constrained control of Unmanned Aerial Vehicles

This paper presents a novel control strategy for an Unmanned Aerial Vehicle subject to state and input constraints. The method consists in pre-stabilizing the system dynamics and then using an Explicit Reference Governor to ensure constraint satisfaction by suitably manipulating the applied reference. The control scheme is initially designed under some simplifying assumptions and is then tuned to ensure robustness even when these assumptions are dropped. The effectiveness of the proposed method is validated numerically.

SOC and SOH estimation for Li-ion batteries based on an equivalent hydraulic model. Part I: SOC and surface concentration estimation

Accurate state-of-charge (SOC) and state-of-health (SOH) estimation is critical to ensure a reliable battery-management system (BMS). This problem is addressed here by resorting to a grey box battery model based on the so-called equivalent hydraulic model (EHM). It allows taking into account in a simple way the difference between bulk concentration and critical surface concentration (CSC) at the anode, which turns out to be significant. The dynamic model is coupled with an output equation based on the Butler-Volmer equation, and the state and parameter of the resulting nonlinear dynamic system are estimated through an extended Kalman filter (EKF). Sufficient conditions for the stability of the EKF are analysed. Finally, the results show that the method provides accurate SOC and CSC. It is shown to outperform two recently proposed approaches for CSC estimation in the considered simulation study. The CSC estimate is used in the companion paper in order to estimate the diffusion coefficient of lithium through the electrode and hence deduce a SOH indicator.

Effect of the visco-elastic properties of thermoplastic polymers on the flexural and rebound behaviours of ski boots for alpine skiing

The flexural behaviour and elastic rebound are the main parameters that determine the global performance of a ski boot during skiing. These two parameters are related to the visco-elastic properties of the polymeric materials used. For this reason, the visco-elastic properties of the materials most utilized for the production of ski boots (polyurethanes and polyolefins) have been studied using dynamic mechanical thermal analysis in a temperature range between −30 °C and +50 °C. Also, the flexural and rebound behaviours of the boot have also been tested using specially designed test benches. The dynamic mechanical thermal analysis results and the flexural and rebound tests results were compared, and a significant effect of the visco-elastic properties on the flexural and rebound behaviour of ski boots was seen. Therefore, dynamic mechanical thermal analysis can be used in a knowledge-based design process of new ski boots in order to improve on-snow performances.

Explicit reference governor for linear systems

ABSTRACT The explicit reference governor is a constrained control scheme that was originally introduced for generic nonlinear systems. This paper presents two explicit reference governor strategies that are specifically tailored for the constrained control of linear time-invariant systems subject to linear constraints. Both strategies are based on the idea of maintaining the system states within an invariant set which is entirely contained in the constraints. This invariant set can be constructed by exploiting either the Lyapunov inequality or modal decomposition. To improve the performance, we show that the two strategies can be combined by choosing at each time instant the least restrictive set. Numerical simulations illustrate that the proposed scheme achieves performances that are comparable to optimisation-based reference governors.