Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Bibliography; leaves 159-166.

Thesis (M.S.)--Tennessee Technological University, 2009. / Title from title page screen (viewed on June 29, 2010). Bibliography: leaves 105-108.

This thesis describes the design of multivariable excitation controllers for synchronous generators, and their practical implementation on a laboratory machine system. The main objectives of the investigation were aimed at extending the steady-state stability limit of the generator and improving its general controllability. The present work is principally concerned with the implementation and test of the designs. Instrumentation has been developed to measure and combine feedback signals; this instrumentation and the laboratory generator system are described in detail. The performances of the controllers are predicted by computer simulation and evaluated by practical testing; attention is focussed on comparison of predicted and experimental performances. The theoretical basis of the design strategy is described, in which an optimal control algorithm applies the system states as feedback signals to the open-loop system, thereby shifting certain of the system eigenvalues to more desirable, predetermined locations. The state variables are selected as physically measurable quantities which obviates the need for implementing state estimation techniques.

In this thesis closed-loop control strategies over a communication network with multiple clients are developed. To accomplish this objective, a steel-ball magnetic-levitation system, a DC motor speed-control system, and an autonomous wheelchair robot referred to as Clients 1, 2, and 3, respectively were used as Networked-Based-control (NCS) test beds to validate the proposed strategies. For real-time operation, Linux with Real-Time Application Interface (RTAI) and Control and Measurement Interface (Comedi) were used as the operating system for Clients 1 and 2. Client 3's software was written in Microsoft Visual Basic 6.0 on the Windows XP operating system (OS). User datagram protocol (UDP) was used as the communication network protocol in this research due to its better real-time performance instead of transmission control protocol (TCP). Although UDP has no guarantee for transferring data, it has smaller overheads and less time delay than TCP. Since the robotic wheelchair and the server are run on different OSs, Samba was used to put both systems into the same LAN with a fast data-transmission speed. Using Samba, the round-trip communication time between the robotic wheelchair and the server is only 11.2 ms whereas 30.8 ms is taken without using Samba. When the server receives the sensor data from multiple clients at the same time, the NCS stability may be deteriorated due to the limitation of the system bandwidth. The NCS stability is affected by the sampling period of the system, and the reduction of the sampling period improves the control loop's performance. However, a shorter sampling period requires more network bandwidth to transmit more sensor data or control data, which increases the network traffic load. Using the PING test, the transmission time for each control loop was measured. The processing time for each system was also measured by a time-stamp function, and the operation time for each control loop was obtained. In order to maintain the NCS stable, several combinations of the sampling periods for each client are suggested and verified. The bandwidth utilization of Client 1 is set to be 43.5% and the range of the bandwidth utilization of Client 2 with guaranteed stability was found to be between 9.1% and 45.3%. Thus, the bandwidth utilization of Client 3 is from 11.8% to 46.8%. The multiple-client NCS test bed could maintain its stability within these ranges of the bandwidth utilizations of all clients.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 1995. / Includes bibliographical references (leaves 108-111).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 81-83). Also available via the Internet.

In 14th August 2003, the Northeast USA suffered its worst power outage event in history. The power disturbance spreading through the system caused mal-trips of the distance relay remote back-up protections, which indeed contributed to the power outage cascading a wide area. The power outage in the Northeast USA was constrained by the presence of HVDC interconnections between the HVAC networks in Ontario and New York. The system collapse did not progress beyond the HVDC interconnection interface with Quebec. The HVDC link can regulate the voltage and current therefore impacts on the performance of the protection and system stability. The distance relay mal-operations were one of the main cause of the Northeast USA blackout as well as the other recent major large area blackouts which were pointed out by the previous papers. This thesis is focus on investigate how HVDC interconnections contribute to maintaining the power system stability. The research work investigated the performance of a distance relay to faults and disturbance on networks containing HVDC interconnection. The research work was carried out by modelling and testing a classic signal processing distance relay in a simple AC network which was based on Kunder’s two areas system using MATLAB/SIMULINK at first. Then the modeled distance relay’s performance was investigated by combining the distance relay and a simple HVDC link based on the Kunder’s two areas system. The research work firstly combined the signal processing distance relay and the HVDC link together to investigate the distance relay’s performance when the protected feeder containing DC link. The distance relay’s performance was investigated when the protected feeders containing HVDC link under fault conditions and power swing conditions. For comparison, a similar power system without HVDC link was also simulated.

In maintaining power system stability; especially that of large interconnected systems, in the face of large disturbances it is desirable to have a non-linear control technique that is simple and inexpensive to implement. This thesis presents a non-linear control technique which relies on angle measurements taken at strategic points in the power system with the aid of the G.P.S. ( Global Positioning System ) timing signal. A method for estimating these bus angles which is faster than previous methods is developed as well as a technique for choosing the locations of these transducers. This transducer placement algorithm aims to place transducers at locations whose bus voltage response to the less well damped inter-area modes is maximised and whose response to the better damped local modes is minimised. Since the control techniques are based on aggregated classical models of coherent generators it is important to be able to estimate the internal voltages of these aggregate machines. The placement algorithm ensures maximally precise angle estimates in the presence of noise by minimising the condition number of the observation matrix relating transducer bus voltages to internal aggregated machine voltages. The non-linear control techniques presented rely on an energy function developed in this thesis which is based on the physical circuit energy of the system. One technique; the Direct Energy technique looks at maximising the negativity of the time rate of change of the energy function, assuming that the energy function is positive during the time frame of interest. It is shown that should the number of controllers be less than the number of modes, excluding the centre of area mode, then sustained oscillations appear which will only be damped by the natural damping of the system. This may be overcome by using techniques which rely on reducing the entire system energy over the time frame of interest. These so-called Lookahead techniques can rely on higher order time derivatives of the energy function or on co-states, the latter being the principal focus of this thesis. The Lookahead control technique developed is based on co-states which are estimated by the using the solution to the time independent Ricatti equation for a LQ model of the system. It is shown to produce good damping in a number of case studies. Furthermore it is shown to perform well in the presence of both static and dynamic load models. Also it is shown that the path dependent terms introduce some ambiguity as to whether or not the system will converge to a stable equilibrium point. It is shown that it is possible to put a bound on the region to which the power system can be assured to converge. Furthermore the addition of the above-mentioned control strategies has the effect of overcoming the effect of the path dependent terms and, should the control action be strong enough, completely swamping them and ensuring system convergence to a stable operating point. In any case the energy function could be directly monitored since all the data needed is being collected anyway for control purposes. / PhD Doctorate

Thesis (Ph. D. electrical engineering)--Washington State University, December 2007. / Includes bibliographical references (p. 112-116).