Adaptive Backstepping Attitude Control of a Rigid Body with State Quantization

Author's accepted manuscript© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper, the attitude tracking control problem of a rigid body is investigated where the states are quantized. An adaptive backstepping based control scheme is developed and a new approach to stability analysis is developed by constructing a new compensation scheme for the effects of the vector state quantization. It is shown that all closed-loop signals are ensured uniformly bounded and the tracking errors converge to a compact set containing the origin. Experiments on a 2 degrees-of-freedom helicopter system illustrate the proposed control scheme.acceptedVersio

Adaptive Control of Systems with Quantization and Time Delays

This thesis addresses problems relating to tracking control of nonlinear systems in the presence of quantization and time delays. Motivated by the importance in areas such as networked control systems (NCSs) and digital systems, where the use of a communication network in NCS introduces several constraints to the control system, such as the occurrence of quantization and time delays. Quantization and time delays are of both practical and theoretical importance, and the study of systems where these issues arises is thus of great importance. If the system also has parameters that vary or are uncertain, this will make the control problem more complicated. Adaptive control is one tool to handle such system uncertainty. In this thesis, adaptive backstepping control schemes are proposed to handle uncertainties in the system, and to reduce the effects of quantization. Different control problems are considered where quantization is introduced in the control loop, either at the input, the state or both the input and the state. The quantization introduces difficulties in the controller design and stability analysis due to the limited information and nonlinear characteristics, such as discontinuous phenomena. In the thesis, it is analytically shown how the choice of quantization level affects the tracking performance, and how the stability of the closed-loop system equilibrium can be achieved by choosing proper design parameters. In addition, a predictor feedback control scheme is proposed to compensate for a time delay in the system, where the inputs are quantized at the same time. Experiments on a 2-degrees of freedom (DOF) helicopter system demonstrate the different developed control schemes.publishedVersio

Driving Factors for Levelized Cost of Energy in Floating Wind Farms

This thesis presents a method for calculating LCOE for offshore floating wind farms. A method has been created that aims to do a life cycle cost analysis, with emphasis on the cost of installation and transportation, and the cost of operation and maintenance for. The method was created to carry out a sensitivity analysis on the effects of various wind farm parameters such as water depth, distance to harbor, wind farm lifetime, capacity factor, wake loss, and the number of wind turbines in the wind farm, on the LCOE of the wind farm. The method was also created to see differences in cost between the three floating platform types: Spar Buoy, Tension Leg Platform, and Semi-Submersible Platform. In 2010 NVE looked at the suitability of 15 locations outside the Norwegian cost for offshore wind farms, Espegren et al. (2010). Four of these locations had water depth suitable for floating platforms. In 2012 another report was published by NVE, looking at the economic suitability of wind farms in the 15 locations, Sydness et al. (2012). The data used in their report has not been made publicly available. In this thesis, data from the dataset NORA3, described by Solbrekke and Sorteberg (2021), has been used, together with a method for calculation of LCOE, to compare the economic potential with that found by NVE for the four locations suitable for floating wind farm, Utsira Nord, Stadthavet, Frøyabanken, and Træna Vest. The results presented in this thesis, points in the same direction as that found by NVE, with some variations. The results presented in this thesis shows the locations Utsira Nord, and Stadthavet as the most economically viable locations, with an LCOE about 15 to 20 e/MWh lower than that found for Frøyabnaken, and Træna Vest. The results of the sensitivity analysis shows that the capacity factor of a lo- cation should be a decisive factor when building a wind farm with low LOCE is the goal. Other factors such as being able to extend the lifetime of the wind farm, and keeping the distance from the wind farm to a port short, was also shown to have a significant effect on lowering the LCOE. The distance to harbor was found to have a great impact on LCOE for large distances. Out of the wind farm parameters investigated, water depth was found to have the least amount of impact on LCOE.Masteroppgave i energiENERGI399MAMN-ENER

Adaptive Quantized Control of Offshore Underactuated Cranes with Uncertainty

Author's accepted manuscript.© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.acceptedVersionPaid open acces

Adaptive Backstepping Control of a 2-DOF Helicopter System with Uniform Quantized Inputs

Author's accepted manuscript© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper proposes a new adaptive controller for a 2-Degree of Freedom (DOF) helicopter system in the presence of input quantization. The inputs are quantized by uniform quantizers. A nonlinear mathematical model is derived for the 2-DOF helicopter system based on Euler-Lagrange equations, where the system parameters and the control coefficients are uncertain. A new adaptive control algorithm is developed by using backstepping technique to track the pitch and yaw position references independently. Only quantized input signals are used in the system which reduces communication rate and cost. It is shown that not only the ultimate stability is guaranteed by the proposed controller, but also the designers can tune the design parameters in an explicit way to obtain the required closed loop behavior. Experiments are carried out on the Quanser helicopter system to validate the effectiveness, robustness and control capability of the proposed scheme.acceptedVersio

Subsea Motion Compensator – Scaled Test at Sea

NORCE has analysed motion data collected from a scaled down version of an offshore floating wind substructure anchored outside Mandal, Norway. The purpose of the test was to demonstrate the effectiveness of a motion compensation system developed by the company North Innovation AS. The sea trail took place during October 2023 collecting data over four days with and without the compensator each. The testing period included severe weather and thus a broad range of conditions providing sufficient data and variations in environmental conditions for fair comparison. Results indicate that the passive motion compensation system is able to dampen both translational and rotational motions, in particular heave, roll and pitch, and especially at higher sea states. It is also during the higher sea states that motion damping is important as these are the critical periods of the operation driving up the cost of the substructure.Subsea Motion Compensator – Scaled Test at SeapublishedVersio

Adaptive quantized control of uncertain nonlinear rigid body systems

This paper investigates the attitude tracking control problem for uncertain nonlinear rigid body systems, where both inputs and states are quantized. It is common in networked control systems that sensor and control signals are quantized before they are transmitted via a communication network. An adaptive backstepping control algorithm is developed for a class of uncertain multiple-input multiple-output (MIMO) systems where a class of sector bounded quantizers is considered. It is shown that all the closed-loop signals are ensured uniformly bounded and tracking is achieved. Further, the tracking errors are shown to converge towards a compact set containing the origin and the set can be made small by the choice of the quantization parameters and the control parameters. For illustration of the proposed control scheme, experiments were conducted on a 2 degrees-of-freedom (DOF) helicopter system.publishedVersio

Adaptive Backstepping Control of a 2-DOF Helicopter System in the Presence of Quantization

Author's accepted manuscript.© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper studies the attitude tracking control for an uncertain 2-degrees of freedom helicopter system where the inputs and the states are quantized. An adaptive backstepping based control scheme is proposed to handle the effect of quantization for tracking of reference angles for pitch and yaw. All closed-loop signals are ensured uniformly bounded and the tracking errors will converge to a compact set containing the origin. Experiments on the helicopter system illustrate the proposed control scheme.acceptedVersio

Control of Spacecraft Formation with Disturbance Rejection and Exponential Gains

We address the problem of state feedback translational motion control of a spacecraft formation through a modified sliding surface controller using variable gains and I^2 action for disturbance rejection. The exponential varying gains ensure faster convergence of the state trajectories during attitude maneuver while keeping the gains small (and the system less stiff) for station keeping. Integral action is introduced for rejection of disturbances with a constant nonzero mean such as aerodynamic drag. A direct consequence is a drop in energy consumption when affected by sensor noise and a decrease in size of the error states residual when operating close to the equilibrium point. A large number of simulation results are presented to show the control performance