535 research outputs found
Linear feedback control of transient energy growth and control performance limitations in subcritical plane Poiseuille flow
Suppression of the transient energy growth in subcritical plane Poiseuille
flow via feedback control is addressed. It is assumed that the time derivative
of any of the velocity components can be imposed at the walls as control input,
and that full-state information is available. We show that it is impossible to
design a linear state-feedback controller that leads to a closed-loop flow
system without transient energy growth.
In a subsequent step, full-state feedback controllers -- directly targeting
the transient growth mechanism -- are designed, using a procedure based on a
Linear Matrix Inequalities approach. The performance of such controllers is
analyzed first in the linear case, where comparison to previously proposed
linear-quadratic optimal controllers is made; further, transition thresholds
are evaluated via Direct Numerical Simulations of the controlled
three-dimensional Poiseuille flow against different initial conditions of
physical interest, employing different velocity components as wall actuation.
The present controllers are effective in increasing the transition thresholds
in closed loop, with varying degree of performance depending on the initial
condition and the actuation component employed
Stability Analysis of Networked Control in Smart Grids
A suitable networked control scheme and its stability analysis framework have been developed for controlling inherent electromechanical oscillatory dynamics observed in power systems. It is assumed that the feedback signals are obtained at locations away from the controller/actuator and transmitted over a communication network with the help of phasor measurement units (PMUs). Within the generic framework of networked control system (NCS), the evolution of power system dynamics and associated control actions through a communication network have been modeled as a hybrid system. The data delivery rate has been modeled as a stochastic process. The closed-loop stability analysis framework has considered the limiting probability of data dropout in computing the stability margin. The contribution is in quantifying allowable data-dropout limit for a specified closed loop performance. The research findings are useful in specifying the requirement of communication infrastructure and protocol for operating future smart grids
Capstan drive transport system for motion picture film
The work presented describes the development of a capstan drive system for the transport of motion picture film. From a model description of the plant and computer aided system design analysis, control algorithms are formulated. The work shows how these relativity complex control algorithms are implemented by making use of the parallel processing capabilities of the transputer.
A critical investigation of current film transport methods is undertaken leading to the design and testing of a prototype capstan drive mechanism. The capstan drive system is
shown to eliminate problems of sprocket drives and their associated mechanisms. A multi-input multi-output controller is presented using state-space methods of design. The developed control strategies are fully tested on a model of the plant before hardware testing. The control outputs of the system are speed and tension. The final control solution
is shown to be a combination of full-state feedback, integral control, and a Kalman filter estimator for the elimination of system disturbances. The transputer implementation of the developed control strategies is presented together with a comparison between simulation and experimental results. It is shown that computational times can be reduced by using multiple transputers and placing computation-intensive
sections of the control algorithm on separate processors. Transputer configurations and interconnections are shown. The capstan system has been shown to allow faster printing speeds with improved transport accuracy leading to better quality of the final picture print. The system has been shown to be 'robust' to external disturbances and changes in plant parameters
Design and application of advanced disturbance rejection control for small fixed-wing UAVs
Small Unmanned Aerial Vehicles (UAVs) have seen continual growth in both research and
commercial applications. Attractive features such as their small size, light weight and
low cost are a strong driver of this growth. However, these factors also bring about some
drawbacks. The light weight and small size means that small UAVs are far more susceptible
to performance degradation from factors such as wind gusts. Due to the generally low
cost, available sensors are somewhat limited in both quality and available measurements.
For example, it is very unlikely that angle of attack is sensed by a small UAV. These
aircraft are usually constructed by the end user, so a tangible amount of variation will
exist between different aircraft of the same type. Depending on application, additional
variation between flights from factors such as battery placement or additional sensors may
exist. This makes the application of optimal model based control methods difficult.
Research literature on the topic of small UAV control is very rich in regard to high
level control, such as path planning in wind. A common assumption in such literature
is the existence of a low level control method which is able to track demanded aircraft
attitudes to complete a task. Design of such controllers in the presence of significant wind
or modelling errors (factors collectively addressed as lumped disturbances herein) is rarely
considered.
Disturbance Observer Based Control (DOBC) is a means of improving the robustness
of a baseline feedback control scheme in the presence of lumped disturbances. The method
allows for the rejection of the influence of unmeasurable disturbances much more quickly
than traditional integral control, while also enabling recovery of nominal feedback con-
trol performance. The separation principle of DOBC allows for the design of a nominal
feedback controller, which does not need to be robust against disturbances. A DOBC
augmentation can then be applied to ensure this nominal performance is maintained even
in the presence of disturbances. This method offers highly attractive properties for control
design, and has seen a large rise in popularity in recent years.
Current literature on this subject is very often conducted purely in simulation. Ad-
ditionally, very advanced versions of DOBC control are now being researched. To make
the method attractive to small UAV operators, it would be beneficial if a simple DOBC
design could be used to realise the benefits of this method, as it would be more accessible
and applicable by many.
This thesis investigates the application of a linear state space disturbance observer to
low level flight control of a small UAV, along with developments of the method needed
to achieve good performance in flight testing. Had this work been conducted purely in
simulation, it is likely many of the difficulties encountered would not have been addressed
or discovered.
This thesis presents four main contributions. An anti-windup method has been devel-
oped which is able to alleviate the effect of control saturation on the disturbance observer
dynamics. An observer is designed which explicitly considers actuator dynamics. This
development was shown to enable faster observer estimation dynamics, yielding better
disturbance rejection performance. During initial flight testing, a significant aeroelastic
oscillation mode was discovered. This issue was studied in detail theoretically, with a pro-
posed solution developed and applied. The solution was able to fully alleviate the effect in
flight. Finally, design and development of an over-actuated DOBC method is presented.
A method for design of DOBC for over actuated systems was developed and studied. The
majority of results in this thesis are demonstrated with flight test data
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