Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: This thesis presents the development of an adaptive longitudinal control system for an unmanned
aerial vehicle (UAV). The project forms part of a research effort at Stellenbosch University
into different fault-tolerant control techniques for UAVs.
In order to demonstrate the usefulness of fault-tolerant adaptive control, the control system
was designed to handle damage-induced longitudinal shifts in the centre of gravity (CG)
of the aircraft, which are known to have a dramatic effect on the stability of a fixed-wing aircraft.
Using a simplified force and moment model, equations were derived which model the
effect of longitudinal CG shifts on the behaviour of the aircraft. A linear analysis of the
longitudinal dynamics using these equations showed that the short period mode can become
unstable for backward CG shifts.
An adaptive pitch rate controller with the model reference adaptive control structure was
designed to re-stabilise the short period mode when the CG shifts backwards. The adaptive
law was designed using Lyapunov stability theory. Airspeed, climb rate and altitude controllers
were designed around the pitch rate controller to allow full autonomous control of
the longitudinal dynamics of the UAV. These outer loops were designed with constant parameters,
since they would be unaffected by CG shifts if the adaptive pitch rate controller
performed as desired.
Pure software simulations as well as hardware-in-the-loop simulations showed that the
adaptive control system is able to handle instantaneous shifts in the centre of gravity which
would destabilise a fixed-gain control system. These simulation results were validated in
flight tests, where the aircraft was destabilised using positive feedback and re-stabilised by
the adaptive control system.
Thus the simulation and flight test results showed that an adaptive control can re-stabilise
an unstable aircraft without explicit knowledge of the change in the aircraft dynamics, and
therefore could be effective as part of an integrated fault-tolerant control system. / AFRIKAANSE OPSOMMING: Hierdie tesis bied die ontwikkeling aan van ’n aanpassende longitudinale beheerstelsel vir ’n
onbemande vliegtuig. Die projek is deel van navorsing by die Universiteit van Stellenbosch
oor verskillende fout-tolerante beheertegnieke vir onbemande vliegtuie.
Om die doeltreffendheid van aanpassende beheer te demonstreer, is die beheerstelsel ontwerp
om situasies te kan hanteer waar die vliegtuig só beskadig word dat sy massamiddelpunt
agtertoe skuif, wat ’n groot invloed op die stabiliteit van ’n vastevlerk-vliegtuig kan
hê.
’n Vereenvoudigde model van die kragte en momente wat op die vliegtuig inwerk is
gebruik om vergelykings af te lei wat beskryf hoe die gedrag van die vliegtuig verander as
die massamiddelpunt agtertoe verskuif. Hierdie vergelykings is gebruik in ’n lineêre analise
van die longitudinale dinamika van die vliegtuig, wat getoon het dat die kortperiode-modus
onstabiel kan raak as die massamiddelpunt agtertoe verskuif.
’n Aanpassende heitempobeheerder met die modelverwysings-aanpassende beheerstruktuur
is ontwerp om die kortperiode-modus weer te stabiliseer wanneer die massamiddelpunt
agtertoe verskuif. Die aanpassingswet is ontwerp deur die gebruik van Lyapunov se stabiliteitsteorie.
Lugspoed-, klimtempo- en hoogtebeheerders is rondom die aanpassende heitempobeheerder
ontwerp sodat die longitudinale dinamika van die vliegtuig heeltemal outonoom
beheer kan word. Hierdie buitelusse is ontwerp met vaste parameters, aangesien
hulle nie geraak sal word deur verskuiwings in die massamiddelpunt as die aanpassende
heitempobeheerder na wense werk nie.
Suiwer sagteware-simulasies, sowel as hardeware-in-die-lus-simulasies, het getoon dat
die aanpassende beheerstelsel oombliklike verskuiwings in die massamiddelpunt goed kan
hanteer, waar sulke verskuiwings ’n beheerstelsel met vaste parameters onstabiel sou maak.
Hierdie simulasie-resultate is bevestig deur vlugtoetse te doen, waar die vliegtuig onstabiel
gemaak is deur positiewe terugvoer, en weer deur die aanpassende beheerstelsel stabiel
gemaak is.
Die simulasie- en vlugtoetsresultate wys dus dat aanpassende beheer ’n onstabiele vliegtuig
weer kan stabiliseer sonder eksplisiete kennis van die veranderinge in die dinamika van
die vliegtuig. Aanpassende beheer kan dus doeltreffend wees as deel van ’n geïntegreerde
fout-tolerante beheerstelsel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17898 |
| Date | 12 1900 |
| Creators | Basson, Willem Albertus |
| Contributors | Engelbrecht, J. A. A., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 176 p. : ill. |
| Rights | Stellenbosch University |
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