Department of Electrical and Electronic Engineering

Permanent URI for this community

https://scholar.sun.ac.za/handle/10019.1/97

Electrical and Electronic Engineering is an exciting and dynamic field. Electrical engineers are responsible for the generation, transfer and conversion of electrical power, while electronic engineers are concerned with the transfer of information using radio waves, the design of electronic circuits, the design of computer systems and the development of control systems such as aircraft autopilots. These sought-after engineers can look forward to a rewarding and respected career.

Browse

Now showing 1 - 20 of 1309

A 10 GHz oversampling delta modulating analogue-to-digital converter implemented with hybrid superconducting digital logic
(Stellenbosch : Stellenbosch University, 2001-03) Fourie, Coenrad Johann; Perold, W. J.; De Swardt, J. B.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: Rapid Single Flux Quantum (RSFQ) logic cells are discussed, and new cells developed. The expected yield of every cell is computed through a Monte Carlo analysis, and where necessary these cells are optimized for use in a complex system. A mathematical study of the Josephson junction and SQUIDs (Superconducting Quantum Interference devices) as switching elements precede a discussion on the operation of RSFQ and COSL (Complementary Output Switching Logic.) These logic families are implemented in low temperature niobium technology, and require liquid helium cooling. A 10 GHz oversampling delta modulating analogue-to-digital converter is then designed and constructed using RSFQ and COSL building blocks in a hybrid configuration. The design emphasis is on devising ways to test the operation of RSFQ with limited equipment. Yield analysis procedures on the complex system are discussed, followed by a detailed discussion on the circuit layout and layout problems. Software routines are developed to calculate the required dimensions of layout structures.
10 kW L-Band planar power combiner
(Stellenbosch : University of Stellenbosch, 2006-12) Fourie, Gerhardus Johannes; Van Niekerk, C.; Van der Walt, P. W.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
This thesis relates to the design and characterization of a 10 kW L-band power combiner consisting of 8 input ports. The design is implemented in a non-radial planar transmission line architecture and operates between 1.2 and 1.4 GHz. Because of the ultra high power requirements for the combiner, special attention is given to the power handling capabilities of the transmission lines and the other components involved. Simulated S-parameter models of connector to stripline transitions and a one to four-way junction, as well as measured S-parameter models of high power terminations are incorporated in the final design. A 10 kW combiner was built and measured at low power only due to time constraints and the limited availability of high power sources. Satisfactory results were obtained in terms of the graceful degradation of unit amplifiers, port mismatches and power combining efficiency.
A 22.2 GHz Antenna for water vapour radiometry
(Stellenbosch : Stellenbosch University, 2019-04) Cerfonteyn, William; De Villiers, D. I. L.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: For this thesis a low-cost antenna solution for a low-cost water vapour radiometry system is designed. The most important specifications for the antenna is that it has to have a -20 dB sidelobe level, a 3° -3 dB beamwidth and have to be electronically steerable. It also has to be low-cost. The first design that is considered is the phased array solution as it can be electronically steered. Since components can be etched onto the design the manufacturing cost is also reduced. The number of elements required for this design to reach the specifications is determined to be more than 16x16 elements, and thus proves to be cost impractical. The analysis is tested by designing a 1x4 and 2x2 multilayered aperture coupled patch antenna array with a corporate feed network, to both test if a better antenna element design can improve the results, and if the analysis is accurate in determining the impracticality of an array design. This also proves that the array design is infeasible. A reflector solution is then considered. The reflector system is designed to statically observe in a few specified directions, removing the need for electronic steering. Two parabolic reflectors and a conical horn is designed. The reflectors are combined through interpolation into one larger reflector. After the horn design proves to be ineffective, a new horn is considered that almost allows the reflector system to meet the specifications. Finally the system is measured, but unfortunately the measured result proves that the physical system does not meet all the specifications. The sidelobe level is around -16 dB, however, the -3 dB beamwidth is well below 3°.
2D Edge-based finite elements for guided and scattered wave problems
(Stellenbosch : Stellenbosch University, 1999-03) Hansmann, Riana Helena; Davidson, D. B.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: This thesis may be divided into two parts: the first describes the Finite Element Method (FEM) and its application to guided wave problems. The second part is devoted to scattering configurations, specifically the use of the Boundary Element Method (BEM) and the hybrid Finite Element Method-Boundary Element Method (FEM-BEM) to obtain solutions for scattering problems. The formulations are restricted to two dimensions throughout the thesis. A variational formulation is introduced and the implementation of boundary conditions is described. The use of vector approximation functions for the Finite Element Method is explained and the advantages highlighted. The properties of these functions are derived and graphical representations are given. A comparison between a lower order and higher order approximation is made. This is applied to problems which demonstrate the capabilities of the Finite Element Method such as ridged waveguides and circular waveguides containing eccentric dielectric rods. Results obtained compare well to analytic solutions, in the cases where these are available. An integral equation for scattering problems is derived. This relates the tangential field components on a contour enclosing a scattering object to the scattered fields and enables a solution to be obtained when the tangential components on the contour are known. It is shown how the interior region enclosed by the contour is discretised and how the Finite Element Method can be coupled with the Boundary Element Method by imposing continuity conditions on the enclosing contour. The resulting system of equations obtained may be solved. Solutions for scattering from perfectly conducting cylinders are obtained and compare well to analytic results.
A 3-axis attitude control system hardware design for a CubeSat
(Stellenbosch : Stellenbosch University, 2014-12) Gerber, Jako; Steyn, W. H.; Stellenbosch University. Faculty of Engineering. Department of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: With CubeSats becoming popular as a cheap alternative to larger satellites, the need for advanced miniature attitude determination and control systems (ADCS) arises to meet the pointing requirements of satellite operations such as earth imaging and orbit maintenance. This thesis describes the design of a complete ADCS for use on CubeSats. A previously designed CubeSat on-board-computer, CubeComputer, and ne sun and nadir sensor, CubeSense, is incorporated in the design. The remaining requirements with regard to sensors and actuators were met by CubeControl, an additional module, the design, manufacturing and testing of which are described. CubeControl can implement magnetic control with the use of a magnetometer and three magnetorquers. It is also capable of driving three reaction wheels for accurate active 3-axis stabilization.
3-Axis geomagnetic magnetometer system design using superconducting quantum interference devices
(Stellenbosch : Stellenbosch University, 2014-04) Kilian, Anton Theo; Fourie, C. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: This work discusses the design of a 3-axis Geomagnetometer SQUID System (GSS), in which HTS SQUIDs are used unshielded. The initial GSS installed at SANSA was fully operable, however the LN2 evaporation rate and SQUID orientation required improving. Magnetic shields were also developed in case the SQUIDs would not operate unshielded and to test the system noise with geomagnetic variations removed. To enable removing the double layer shield from the probes while the SQUIDs remain submerged in LN2, the shield was designed to disassemble. The shields proved to be effective, however due to icing the shields could not be removed without removing the SQUIDs from the LN2.
3-D face recognition
(Stellenbosch : Stellenbosch University, 1999-12) Eriksson, Anders; Weber, D.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical & Electronic Engineering.
ENGLISH ABSTRACT: In recent years face recognition has been a focus of intensive research but has still not achieved its full potential, mainly due to the limited abilities of existing systems to cope with varying pose and illumination. The most popular techniques to overcome this problem are the use of 3-D models or stereo information as this provides a system with the necessary information about the human face to ensure good recognition performance on faces with largely varying poses. In this thesis we present a novel approach to view-invariant face recognition that utilizes stereo information extracted from calibrated stereo image pairs. The method is invariant of scaling, rotation and variations in illumination. For each of the training image pairs a number of facial feature points are located in both images using Gabor wavelets. From this, along with the camera calibration information, a sparse 3-D mesh of the face can be constructed. This mesh is then stored along with the Gabor wavelet coefficients at each feature point, resulting in a model that contains both the geometric information of the face as well as its texture, described by the wavelet coefficients. The recognition is then conducted by filtering the test image pair with a Gabor filter bank, projecting the stored models feature points onto the image pairs and comparing the Gabor coefficients from the filtered image pairs with the ones stored in the model. The fit is optimised by rotating and translating the 3-D mesh. With this method reliable recognition results were obtained on a database with large variations in pose and illumination.
3D tracking between satellites using monocular computer vision
(Stellenbosch : University of Stellenbosch, 2005-03) Malan, Daniel Francois; Steyn, W. H.; Herbst, B. M.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
Visually estimating three-dimensional position, orientation and motion, between an observer and a target, is an important problem in computer vision. Solutions which compute threedimensional movement from two-dimensional intensity images, usually rely on stereoscopic vision. Some research has also been done in systems utilising a single (monocular) camera. This thesis investigates methods for estimating position and pose from monocular image sequences. The intended future application is of visual tracking between satellites flying in close formation. The ideas explored in this thesis build on methods developed for use in camera calibration, and structure from motion (SfM). All these methods rely heavily on the use of different variations of the Kalman Filter. After describing the problem from a mathematical perspective we develop different approaches to solving the estimation problem. The different approaches are successfully tested on simulated as well as real-world image sequences, and their performance analysed.
3D turning analysis of a Bipedal Robot
(Stellenbosch : Stellenbosch University, 2022-04) Pretorius, Dean; Fisher, Callen; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: There is stark contrast between the abilities of legged locomotion found in nature, and locomotion found in lab environments. This performance gap is indicative of a large knowledge gap. Roboticists are required to bridge these gaps to truly invite robots to detach from their support rigs, and actuate within the real world. In this thesis, non-planar contact and discontinuous locomotive dynamics were modeled as a trajectory optimization problem. Consequently, this made understanding the complexities of legged locomotion more tractable. Understanding, and being able to leverage, contact is crucial to successful legged locomotion. Therefore, a comprehensive investigation was conducted into non-planar contact dynamics using a monopod robot. Here, methods of modeling the Coulomb friction cone in contact implicit trajectory optimization were implemented. Literature suggests replacing the friction cone with a polyhedral approximation thereof. However, this method is known to underestimate the resultant friction in non-planar environments. This thesis presents a novel method of modeling the 3D friction cone and compares it to an implementation of the polyhedral approximation. Results from this comparison show that the novel method was significantly more computationally efficient than the polyhedral approximation, without underestimating the friction cone. Dynamic bipedal locomotion remains a struggle for most robotic platforms. Robotics literature provides few examples of robots achieving agile, dynamic locomotion. Therefore, trajectories realizing non-planar dynamic bipedal motion were generated. Experiments were conducted into acceleration, steady-state, deceleration, and rapid turning off the sagittal plane. Optimal trajectories displayed the robot walking at speeds resulting in a Froude number less than 0.5, and running at speeds resulting in a higher Froude number. This is consistent with dynamic gaits found in nature. A sliding-mass velocity profile emerged when conducting long-time-horizon trajectories where the robot accelerated from a rest position and decelerated back to rest after completing multiple steps in a periodic steady-state gait. Additionally, when turning off the sagittal plane, slip occurred at least 93.32% of the duration of contact, and turn overshoot is present in all turn trajectories.
A computational architecture for real-time systems
(Stellenbosch : Stellenbosch University, 2000-12) Mostert, Sias; Du Plessis, J. J.; Halang, W. A.; Stellenbosch University. Faculty of Engineering. Dept.of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: The engineering of dependable real-time systems for mission critical applications is a resource intensive and error prone process. Achieving dependability requires a general consensus on the correctness of a system with regard to its intended function. For a consensus to be achieved, the properties of the system must be well understood which, in turn, requires consensus on a rigorously defined computational architecture. There is currently no single agreed upon computational architecture at the application level which can serve as a common denominator for the design and implementation of real-time systems. It is the thesis of this dissertation that a rigorous computational architecture, applicable from design to implementation, enables engineers to better understand software for real-time systems. To substantiate this claim, the real-time data flow architecture RDF with its notation allowing the description of complete systems from design to implementation will be explored. Four distinct research areas for improving the engineering process of real-time systems are dealt with in the dissertation: 1) the development of an architecture for real-time systems being suitable for design and implementation in software and hardware, 2) the consolidation of a number of graphical languages into a graphical notation for functional specification, design and construction of real-time systems, 3) the development of a simple processor architecture for the execution of real-time applications, and 4) and the evaluation of the architecture in the framework of a microsatellite case study. In particular, the following original contributions are made: 1) the firing semantics of data flow systems are expanded to include disjunctive firing semantics in a novel way in addition to the classical conjunctive firing semantics, 2) the inherent real-time data flow property, Le. that a receiving task must be ready to receive the next incoming message when it is sent, is extended to the synchronous data flow model, 3) a notation for describing all properties of real-time systems is defined 'with the real-time data flow language RDF as base language, 4) two hardware processor architectures are introduced that offer one-to-one correspondence between design and implementation and, thus, reduce the semantic gap between design language and program execution, and 5) the class of systems that can be modelled with data flow architectures is shown to include control systems and data flow systems. The language set and processor architecture were applied to certain aspects of the SUNSAT microsatellite project.
A multi-mode attitude determination and control system for small satellites
(Stellenbosch : Stellenbosch University, 1995-12) Steyn, Willem Hermanus; Schoonwinkel, A.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: New advanced control techniques for attitude determination and control of small (micro) satellites are presented. The attitude sensors and actuators on small satellites are limited in accuracy and performance due to physical limitations, e.g. volume, mass and power. To enhance the application of sophisticated payloads such as high resolution imagers within these confinements, a multi-mode control approach is proposed, whereby various optimized controller functions are utilized during the orbital life of the satellite. To keep the satellite's imager and antennas earth pointing with the minimum amount of control effort, a passive gravity gradient boom, active magnetic torquers and a magnetometer are used. A "cross-product" detumbling controller and a robust Kalman filter angular rate estimator are presented for the preboom deployment phase. A fuzzy controller and magnetometer full state extended Kalman filter are presented for libration damping and Z-spin rate control during inactive imager periods. During imaging, when high performance is required, additional fine resolution earth horizon, sun and star sensors plus 3-axis reaction wheels are employed. Full state attitude, rate and disturbance estimation is obtained from a horizon/sun extended Kalman filter. A quaternion feedback reaction wheel controller is presented to point or track a reference attitude during imaging. A near-minimum time, eigenaxis rotational reaction wheel controller for large angular maneuvers. Optimal linear quadratic and minimum energy algorithms to do momentum dumping using magnetic torquers, are presented. A new recursive magnetometer calibration method is designed to enhance the magnetic in-flight measurements. Finally, a software structure is proposed for the future onboard implementation of the multi-mode attitude control system.
Accelerating deep reinforcement learning for autonomous racing
(Stellenbosch : Stellenbosch University, 2023-03) Evans, Benjamin; Jordaan, Willem; Engelbrecht, Herman; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: The F1/10th racing problem is to use the onboard LiDAR scan to calculate speed and steering references to move a 1/10th scale car around the track as quickly as possible. While planning has typically used perception, planning and control pipelines, recently, deep reinforcement learning (DRL) has grown in popularity due to its advantages of not requiring explicit state representation and environmental flexibility. Current approaches have suffered from poor performance at low speeds, safety concerns exacerbated by sim-toreal transfer, and few approaches have considered obstacle avoidance. The first contribution of this work is the development of high-speed learning formulations for autonomous racing. A comprehensive evaluation of previous approaches concludes that current learning formulations train agents to select infeasible speed profiles, resulting in the agents being unable to race using the vehicle’s full speed profile. This problem is overcome by using analytical vehicle models to develop learning formulations for improved speed selection. The performance evaluation shows that the novel formulations enable the vehicle to learn a feasible speed profile using the vehicle’s full speed range and achieve lower lap times than previous methods in the literature. This result indicates that using vehicle models improves high-performance racing behaviour. The second contribution of this work is to enable online learning by using a supervisory safety system (SSS). A safety system is designed that uses viability theory to ensure vehicle safety, irrespective of the planner used. The SSS is incorporated into the learning formulation and used to train DRL agents to race without them ever crashing. The novel learning formulation is extensively evaluated in simulation, demonstrating that online training can train agents to race without ever crashing, achieve a 10× improvement in sample efficiency and that the trained agents select conservative speed profiles. The proposed method is validated at constant speed on a physical vehicle, demonstrating that an agent can be trained from random to drive around a track without ever crashing. The final contribution of this work is to explore how DRL agents can be used to expand the ability of current classical planners to avoid unmapped obstacles. Three hybrid architectures that combine classical and learning components are presented and evaluated. The modification planner, which combines a path follower and DRL agent in parallel, demonstrates the ability to track a reference path while avoiding unmapped obstacles. The results indicate that combining classical and DRL components can improve the performance of DRL agents while enabling classical solutions to avoid obstacles.
Accelerating the method of moments implementation on FPGA hardware
(Stellenbosch : Stellenbosch University, 2021-12) Mnisi, Caleb; Ludick, Danie; Barnard, Arno; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: Advances in transistor technology have reached a point where the physical limitations on chip design means that we are starting to approach a decline in the curve that used to follow Moore’s law. Engineers and Scientists are now turning to Hyper-Scale computing and parallel systems to be able to continue the trend of Moore’s law and offset this decreased cadence. This naturally means that the traditional way of running operations also has to be revised to facilitate implementation on parallel systems. This project aims to develop hardware architecture that optimizes the computation of electromagnetic problems using the Method of Moments (MoM) formulation on field programmable gate array (FPGA) hardware. This can be accomplished by exploiting inherent properties in the formulation that allow for parallel computation of independent sections, and then running these computations in parallel, using dedicated computation units on the FPGA fabric. FPGAs and reconfigurable systems provide a combination of low power consumption and flexibility for applications in computation. We aim to exploit the reconfigurable structure of the FPGA to help facilitate the development of the hardware architecture. The configurable interconnect of the FPGA also allows us to arrange the FPGA resources in a manner that will optimize the specific computation and thus reduce the computation time.
Acceleration based manoeuvre flight control system for unmanned aerial vehicles
(Stellenbosch : Stellenbosch University, 2008-12) Peddle, Iain K.; Jones, T.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: A strategy for the design of an effective, practically feasible, robust, computationally efficient autopilot for three dimensional manoeuvre flight control of Unmanned Aerial Vehicles is presented. The core feature of the strategy is the design of attitude independent inner loop acceleration controllers. With these controllers implemented, the aircraft is reduced to a point mass with a steerable acceleration vector when viewed from an outer loop guidance perspective. Trajectory generation is also simplified with reference trajectories only required to be kinematically feasible. Robustness is achieved through uncertainty encapsulation and disturbance rejection at an acceleration level. The detailed design and associated analysis of the inner loop acceleration controllers is carried out for the case where the airflow incidence angles are small. For this case it is shown that under mild practically feasible conditions the inner loop dynamics decouple and become linear, thereby allowing the derivation of closed form pole placement solutions. Dimensional and normalised non-dimensional time variants of the inner loop controllers are designed and their respective advantages highlighted. Pole placement constraints that arise due to the typically weak non-minimum phase nature of aircraft dynamics are developed. A generic, aircraft independent guidance control algorithm, well suited for use with the inner loop acceleration controllers, is also presented. The guidance algorithm regulates the aircraft about a kinematically feasible reference trajectory. A number of fundamental basis trajectories are presented which are easily linkable to form complex three dimensional manoeuvres. Results from simulations with a number of different aircraft and reference trajectories illustrate the versatility and functionality of the autopilot. Key words: Aircraft control, Autonomous vehicles, UAV flight control, Acceleration control, Aircraft guidance, Trajectory tracking, Manoeuvre flight control.
Acceleration based manoeuvre flight control system for unmanned aerial vehicles
(Stellenbosch : Stellenbosch University, 2008-12) Peddle, Iain K.; Jones, T.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
A strategy for the design of an effective, practically feasible, robust, computationally efficient autopilot for three dimensional manoeuvre flight control of Unmanned Aerial Vehicles is presented. The core feature of the strategy is the design of attitude independent inner loop acceleration controllers. With these controllers implemented, the aircraft is reduced to a point mass with a steerable acceleration vector when viewed from an outer loop guidance perspective. Trajectory generation is also simplified with reference trajectories only required to be kinematically feasible. Robustness is achieved through uncertainty encapsulation and disturbance rejection at an acceleration level. The detailed design and associated analysis of the inner loop acceleration controllers is carried out for the case where the airflow incidence angles are small. For this case it is shown that under mild practically feasible conditions the inner loop dynamics decouple and become linear, thereby allowing the derivation of closed form pole placement solutions. Dimensional and normalised non-dimensional time variants of the inner loop controllers are designed and their respective advantages highlighted. Pole placement constraints that arise due to the typically weak non-minimum phase nature of aircraft dynamics are developed. A generic, aircraft independent guidance control algorithm, well suited for use with the inner loop acceleration controllers, is also presented. The guidance algorithm regulates the aircraft about a kinematically feasible reference trajectory. A number of fundamental basis trajectories are presented which are easily linkable to form complex three dimensional manoeuvres. Results from simulations with a number of different aircraft and reference trajectories illustrate the versatility and functionality of the autopilot. Key words: Aircraft control, Autonomous vehicles, UAV flight control, Acceleration control, Aircraft guidance, Trajectory tracking, Manoeuvre flight control.
The accuracy of electromagnetic equivalence theorem models of microstrip patch antennas
(Stellenbosch : Stellenbosch University, 1991) Theron, Isak Petrus; Cloete, J. H.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: In this report the application of an equivalence theorem model to a patch in a microstrip medium is considered. The problem originated with the application of the Leontovich boundary condition to an equivalent surface current in a moment method technique used by Mosig and Gardiol [1, 2] for the analysis of microstrip antennas and circuits. Their formulation consists of an equivalent electric source Js which satisfies a boundary condition Et = Zs Js. They thus apply a physical boundary condition to an equivalent source, completely ignoring the magnetic sources in the equivalent model. This approximation is analyzed to assess its accuracy. The Leontovich boundary condition is examined and it is found to be applicable to the physical or true current on a patch. The full equivalence model is then developed and compared to the Leontovich model to find the relationship between the true current flowing on the conductor and the equivalent current. It is found that, although the equivalent electric current is equal to the true current on each of the two sides of the patch, an equivalent magnetic current also exists. The contribution of this current to the total field is then examined for a patch on a single dielectric layer above a ground plane. This also gives an idea of what to expect in the case of a multi layered medium. To do the comparison the fields (also called Green's functions) radiated by an electric and a magnetic dipole on the surface of the dielectric are determined from the boundary conditions. This is done in the spectral domain and the spatial fields are then found by an inverse Fourier transform. The spectral functions are too complicated to have closed form solutions in the near field region and thus the integrals are solved numerically using the Hankel transform. The dipoles are scaled according to a relation between the electric and magnetic currents resulting from the application of the equivalence theorem. It is found that, for frequencies up to 30 GHz, the contribution of the magnetic current can be ignored over the whole region p ≠ 0 with an error of less than 0.5%. (This is for a pure copper patch on a substrate with Er = 2.5 and thickness of 0.04 λ.) At the point p = 0 the magnetic current causes a discontinuity in the electric field normal to the dipole axis and tangential to the surface of the dielectric. In the last chapter of this report a theory is developed assuming that the tangential electric fields on top of the patch are negligible in comparison to those on the bottom. The magnetic current then causes a jump in the field to comply with the condition of zero fields in the conductor. This is also the value of the tangential fields directly above the conductor. The boundary condition is then applied on the dielectric side of the patch while ignoring the magnetic sources completely. The value of the error in ignoring the magnetic sources is thus quantified enabling the accuracy of the approximations to be analyzed for any particular application.
Accurate autonomous landing of a fixed-wing unmanned aerial vehicle
(Stellenbosch : Stellenbosch University, 2012-12) Alberts, Frederik Nicolaas; Jones, T.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: This thesis presents the analysis, design, simulation and practical implementation of a control system to achieve an accurate autonomous landing of a fixed-wing unmanned aerial vehicle in the presence of wind gust atmospheric disturbances. Controllers which incorporate the concept of direct-lift control were designed based on a study of the longitudinal dynamics of the UAV constructed as a testbed. Direct-lift control offers the prospect of an improvement in the precision with which aircraft height and vertical velocity can be controlled by utilising actuators which generate lift directly, instead of the conventional method whereby the moment produced by an actuator results in lift being indirectly generated. Two normal specific acceleration controllers were designed. The first being a conventional moment-based controller, and the second a direct-lift-augmented controller. The moment-based controller makes use of the aircraft’s elevator while the direct-lift augmented controller in addition makes use of the flaps of the aircraft which serve as the direct-lift actuator. Controllers were also designed to regulate the airspeed, altitude, climb rate, and roll angle of the aircraft as well as damp the Dutch roll mode. A guidance controller was implemented to allow for the following of waypoints. A landing procedure and methodology was developed which includes the circuit and landing approach paths and the concept of a glide path offset to calibrate the touchdown point of a landing. All controllers and the landing procedure were tested in a hardware-in-the-loop simulation environment as well as practically in a series of flight tests. Five fully autonomous landings were performed, three of these using the conventional NSA controller, and the final two the direct-lift-augmented NSA controller. The results obtained during the landing flight tests show that the project goal of a landing within five meters along the runway and three meters across the runway was achieved in both normal wind conditions as well as in conditions where wind gusts prevailed. The flight tests also showed that the direct-lift-augmented NSA controller appears to achieve a more accurate landing than the conventional NSA controller, especially in the presence of greater wind disturbances. The direct-lift augmented NSA controller also exhibited less pitch angle rotation during landing.
Accurate autonomous landing of a fixed-wing unmanned aircraft under crosswind conditions
(Stellenbosch : Stellenbosch University, 2017-03) De Bruin, Andrew; Jones, Thomas; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: This thesis presents the design, implementation and verification of an autopilot system with strong disturbance rejection characteristics, capable of landing a fixed-wing unmanned aircraft accurately under crosswind conditions. All aspects of the autopilot design are considered, from first principles to the final practically verified product. A mathematical aircraft model is derived, verified and analysed in detail to ensure the design of a high-fidelity, high-bandwidth flight control system. A synergistic controller architecture is proposed, where the approach is to design a structure capable of executing one of three crosswind landing techniques, or a combination thereof, by strategically sequencing controllers throughout the landing procedure. Various landing techniques, developed for manned aircraft, are investigated and emulated by the flight control system to exploit the advantages of each and to mitigate the risks associated with crosswind landings. A highbandwidth acceleration-based control architecture was augmented with Direct Lift Control to improve gust alleviation performance in the aircraft’s longitudinal axis. A state machine was used to facilitate effective controller sequencing and continuous hierarchical monitoring through strategically planned state transitions. Monte Carlo simulations were used to develop a landing accuracy prediction system that provides statistical information regarding the expected touchdown region given certain atmospheric conditions. Results from sixteen days of flight tests demonstrate the autopilot’s success, and correspond exceptionally well with results obtained from high-fidelity hardware-in-the-loop simulations. Verification of the autopilot through practical flight testing and extensive simulations proved that the system is capable of performing crosswind landings accurate to within 0.5 m of the intended touchdown point.
Accurate localisation of a multi-rotor using monocular vision
(Stellenbosch : Stellenbosch University, 2018-03) Blom, Josua; Wiid, P. G.; Van Daalen, C. E.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
ENGLISH ABSTRACT: The mid-frequency aperture array (MFAA) is planned for phase two of the square kilometre array project, which has its design phase scheduled for 2018. The MFAA's antenna arrays need to be characterised in their real world environment. The antenna array characterisation can be done with a test source mounted on a multi-rotor which is own over the antennas. However, the test source needs to be localised accurately relative to the antenna array, which is currently achieved by expensive and cumbersome methods. Accurate vision-based localisation is one possible inexpensive solution, provided arti cial reference points can be placed in the environment. Many vision-based localisation methods exist; however, the focus is often on simultaneous localisation and mapping as opposed to localisation only. The problem is simpli ed signi cantly when arti cial reference points, referred to as landmarks, are manually placed in the environment wherein the multi-rotor needs to be localised. The focus of the research presented in this thesis is therefore on accurate localisation of a multi-rotor aircraft specifically through monocular vision using manually placed artificial landmarks. The multi-rotor's state propagation was described according to a kinematic motion model. Additionally, a measurement model was designed which relates camera image measurements to the system's states. A localisation algorithm using the unscented Kalman filter (UKF) was designed and integrated. The UKF uses the sensor data from the multi-rotor as well as measurements derived from image processing to best estimate the pose of the multi-rotor. The localisation algorithm was first tested and refined in simulation, after which experimental flight tests were performed and the resulting data sets were analysed. The experimental results are promising; the algorithm localised the multi-rotor with a mean accuracy of around six centimetres relative to a differential GPS (DGPS) that was used as a baseline. A high quality DGPS can localise at an accuracy of up to two centimetres; however, the Piksi DGPS used in this project proved to be intermittently accurate and unreliable. The current accuracy of the localisation algorithm would be suitable for other radio telescope antenna arrays which operate at lower frequencies than the MFAA. However, with some improvements in hardware integration, it should be possible to achieve better accuracy than differential GPS systems at a fraction of the cost, making it a promising solution for localisation in antenna characterisation application on the MFAA.
Accurate modelling and realisation of a 4th generation wireless communication system
(Stellenbosch : University of Stellenbosch, 2006-12) Schulze, Shaun; Palmer, K. D.; Kuhnert, C.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
A great demand exits for higher data rates and increased reliability of future consumer based mobile communication systems while being more bandwidth and power efficient. Orthogonal frequency division multiplexing (OFDM) in combination with multiple-input multiple-output (MIMO) schemes has become a promising candidate for fulfilling the demand of next generation communication systems. The sensitivity of MIMO OFDM systems to physical impairments is of great interest and particularly the Alamouti space-time block code is under investigation in this thesis. Generic and comprehensive simulation models of an OFDM communication system incorporating the spacetime block code are developed in a modular fashion and used in a performance evaluation with non-ideal component and channel behaviour.

Browse

Browsing Department of Electrical and Electronic Engineering by Title

Results Per Page

Sort Options