Decoupling and adaptive control and stabilization of two-link elastic robotic arm

In this thesis the control and stabilization of a two link flexible robotic arm is considered. The first scheme is based on nonlinear inversion, a nonlinear controller is designed for the trajectory control of the joint angles using joint torquers. The inverse controller includes a servocompensator for robustness. A simplified controller has also been designed neglecting the Coriolis and Centrifugal forces; In the second scheme the control system design is based on nonlinear adaptive control and linear stabilization. First a nonlinear adaptive control law is derived such that in the closed-loop system the joint-angles are precisely controlled to track reference trajectories. A linear stabilizer designed based on a linear model of the arm is switched to accomplish the final capture of the desired state; Simulation results are presented for all cases to show that in the closed-loop system accurate joint angle trajectory tracking and elastic mode stabilization can be accomplished inspite of the uncertainity in the payload. (Abstract shortened with permission of author.) ftn*This research was supported by the U.S. Army Research Office under ARO Grant No. DAAL03-87-G-004

A novel method for power system stabilizer design

Power system stability is defined as the condition of a power system that enables it to remain in a state of operating equilibrium under normal operating conditions and to regain an acceptable state of equilibrium after being subjected to a finite disturbance. In the evaluation of stability, the focus is on the behavior of the power system when subjected to both large and small disturbances. Large disturbances are caused by severe changes in the power system, e.g. a short-circuit on a transmission line, loss of a large generator or load, loss of a tie-line between two systems. Small disturbances in the form of load changes take place continuously requiring the system to adjust to the changing conditions. The system should be capable of operating satisfactorily under these conditions and successfully supplying the maximum amount ofload. Power system stability is defined as the condition of a power system that enables it to remain in a state of operating equilibrium under normal operating conditions and to regain an acceptable state of equilibrium after being subjected to a finite disturbance. In the evaluation of stability, the focus is on the behavior of the power system when subjected to both large and small disturbances. Large disturbances are caused by severe changes in the power system, e.g. a short-circuit on a transmission line, loss of a large generator or load, loss of a tie-line between two systems. Small disturbances in the form of load changes take place continuously requiring the system to adjust to the changing conditions. The system should be capable of operating satisfactorily under these conditions and successfully supplying the maximum amount ofload. This dissertation deals with the use of Power System Stabilizers (PSS) to damp electromechanical oscillations arising from small disturbances. In particular, it focuses on three issues associated with the damping of these oscillations. These include ensuring robustness of PSS under changing operating conditions, maintaining or selecting the structure of the PSS and coordinating multiple PSS to ensure global power system robustness. To address the issues outlined above, a new PSS design/tuning method has been developed. The method, called sub-optimal Hoo PSS design/tuning, is based on Hoo control theory. For the implementation of the sub-optimal Hoo PSS design/tuning method, various standard optimization methods, such as Sequential Quadratic Programming (SQP), were investigated. However, power systems typically have multiple "modes" that result in the optimization problem being non-convex in nature. To overcome the issue of non-convexity, the optimization algorithm, embedded in the 111 University of Cape Town sub-optimal Hoo PSS design/tuning method, is based on Population Based Incremental Learning (PBIL). This new sub-optimal Heo design/tuning method has a number of important features. The method allows for the selection of the PSS structure i.e. the designer can select the order and structure of the PSS. The method can be applied to the full model of the power system i.e. there is no need for using a reduced-order model. The method is based on Heo control theory i.e. it uses robustness as a key objective. The method ensures adequate damping of the electromechanical oscillations of the power system. The method is suitable for optimizing existing PSS in a power system. This method improves the overall damping of the system and does not affect the observability of the system poles. To demonstrate the effectiveness of the sUb-optimal Hoo PSS design/tuning method, a number of case studies are presented in the thesis. The sub-optimal Hoo design/tuning method is extended to allow for the coordinated tuning of multiple controllers. The ability to tune multiple controllers in a coordinated manner allows the designer to focus on the overall stability and robustness of the power system, rather than focusing just on, the local stability of the system as viewed from the generator where the controllers are connected

A Study on Fault Tolerant Wide-Area Controller Design to Damp Inter-Area Oscillations in Power Systems

Due to increased power supply demand, power system oscillations has become a major concern to have stable and secure system operation. One of the major concern in a power system is to damp inter-area oscillations. Lack of proper damping of oscillations may limit power transfer capability and blackouts. Power system stabilizer is used to damp local oscillations but not efficient to damp inter-area oscillations due to less observability of wide-area signals. Wide-Area Measurement Systems is used to overcome this issue and damp inter-area modes to an adequate level. In order to select feedback signals and controller location, wide-area loop selection method using geometrical measure approach is performed. However, while obtaining local and remote signals, a time-delay is introduced that may degrade the performance of system or may lead to instability. Two configurations are defined depending on feedback i.e. synchronous and non-synchronous feedback and modeled with 2nd order Pade approximation. The controller is synthesized based on H8 mixed sensitivity method with regional pole placement for a 4 machine 11 bus power system. It can be found that WDC damps out oscillations quickly and improves performance. Next problem considered is to design a controller when there is a sudden loss of remote signal. A conventional control (CC) method is used to design controller considering a local signal always available and a comparison is made in plants performance for normal and faulty conditions. It is found that conventional control method degrades performance in faulty situation and may lead to instability. To address this problem, a passive fault tolerant control (FTC) method is used where an iterative procedure is used and found that the system maintains adequate stability even in faulty conditions. For FTC method, the control effort required was more compared to CC method but FTC provides acceptable performance than CC controller

Passive Stability And Actuation Of Micro Aerial Vehicles

Micro Aerial Vehicles (MAVs) have increased in popularity in recent years. The most common platform, the quadrotor, has surpassed other MAVs like traditional helicopters and ornithopters in popularity mainly due to their simplicity. Yet the quadrotor design is a century old and was intended to carry people. We set out to design a MAV that is designed specifically to be a MAV, i.e. a vehicle not intended to carry humans as a payload. With this constraint lifted the vehicle can continuously rotate, which would dizzy a human, can sustain larger forces, which would damage a human, or can take advantage of scaling properties, where it may not work at human scale. Furthermore, we aim for simplicity by removing vehicle controllers and reducing the number of actuators, such that the vehicle can be made cost effective, if not disposable. We begin by studying general equations of motion for hovering MAVs. We search for vehicle configurations that exhibit passive stability, allowing the MAV to operate without a controller or actuators to apply control, ideally a single actuator. The analysis suggests two distinct types of passively stabilized MAVs and we create test vehicles for both. With simple hovering achieved, we concentrate on controlled motion with an emphasis on doing so without adding actuators. We find we can attain three degree of freedom control using separation of time scales with our actuator via low frequency for control in the vertical direction and high frequency for control in the horizontal plane. We explore techniques for achieving high frequency actuator control, which also allow the compensation of motor defects, specifically cogging torque. We combine passive stability with the motion control into two vehicles, UNO and Piccolissimo. UNO, the Underactuated-propeller Naturally-stabilized One-motor vehicle, demonstrates the capabilities of simple vehicles by performing maneuvers like conventional quadrotors. Piccolissimo, Italian for “very little”, demonstrates the merits of passive stability and single actuator control by being the smallest, self-powered, controllable MAV

A novel method for power system stabilizer design

Word processed copy.Includes bibliographies.Power system stability is defined as the condition of a power system that enables it to remain in a state of operating equilibrium under normal operating conditions and to regain an acceptable state of equilibrium after being subjected to a finite disturbance. In the evaluation of stability, the focus is on the behavior of the power system when subjected to both large and small disturbances. Large disturbances are caused by severe changes in the power system, e.g. a short-circuit on a transmission line, loss of a large generator or load, loss of a tie-line between two systems. Small disturbances in the form of load changes take place continuously requiring the system to adjust to the changing conditions. The system should be capable of operating satisfactorily under these conditions and successfully supplying the maximum amount ofload. This dissertation deals with the use of Power System Stabilizers (PSS) to damp electromechanical oscillations arising from small disturbances. In particular, it focuses on three issues associated with the damping of these oscillations. These include ensuring robustness of PSS under changing operating conditions, maintaining or selecting the structure of the PSS and coordinating multiple PSS to ensure global power system robustness

An adaptive human response mechanism controlling the V/STOL aircraft. Appendix 3: The adaptive control model of a pilot in V/STOL aircraft control loops

Importance of the role of human operator in control systems has led to the particular area of manual control theory. Human describing functions were developed to model human behavior for manual control studies to take advantage of the successful and safe human operations. A single variable approach is presented that can be extended for multi-variable tasks where a low order human response model is used together with its rules, to adapt the model on-line, being capable of responding to the changes in the controlled element dynamics. Basic control theory concepts are used to combine the model, constrained with the physical observations, particularly, for the case of aircraft control. Pilot experience is represented as the initial model parameters. An adaptive root-locus method is presented as the adaptation law of the model where the closed loop bandwidth of the system is to be preserved in a stable manner with the adjustments of the pilot handling qualities which relate the latter to the closed loop bandwidth and damping of the closed loop pilot aircraft combination. A Kalman filter parameter estimator is presented as the controlled element identifier of the adaptive model where any discrepancies of the open loop dynamics from the presented one, are sensed to be compensated

Quadruplex digital flight control system assessment

Described are the development and validation of a double fail-operational digital flight control system architecture for critical pitch axis functions. Architectural tradeoffs are assessed, system simulator modifications are described, and demonstration testing results are critiqued. Assessment tools and their application are also illustrated. Ultimately, the vital role of system simulation, tailored to digital mechanization attributes, is shown to be essential to validating the airworthiness of full-time critical functions such as augmented fly-by-wire systems for relaxed static stability airplanes

Design of power system stabilizers using evolutionary algorithms

Includes synopsis.Includes bibliographical references (leaves 151-159).Includes bibliographical references (leaves 125-134).Over the past decades, the issue of low frequency oscillations has been of major concern to power system engineers. These oscillations range from 0.1 to 3Hz and tend to be poorly damped especially in systems equipped with high gain fast acting AVRs and highly interconnected networks. If these oscillations are not adequately damped, they may sustain and grow, which may lead to system separation and loss of power transfer