This thesis presents a novel technique for prediction of the transient stability status of a power system following a large disturbance such as a fault, and application of the tech-nique for subsequent emergency control. The prediction is made based on the synchro-nously measured samples of the magnitudes of fundamental frequency voltage phasors at major generation/load centers. The voltage samples are taken immediately after a fault is cleared and used as inputs to a binary classifier based on support vector machines to iden-tify the transient stability condition. The classifier is trained using examples of the post-fault recovery voltages (inputs) obtained through simulations and the corresponding sta-bility status (output) determined using a power angle-based stability index. Studies with the New England 39-bus test system indicate that the proposed algorithm can correctly recognize when the power system is approaching transient instability. The proposed sys-tem is then applied to Venezuelan power system and Manitoba Hydro power grid to demonstrate the applicability for large practical power systems. Performance of the pro-posed transient stability prediction scheme under the presence of asymmetrical faults, voltage sensitive loads, unlearned network topologies and measurement noise was found to be satisfactory. Once an impending transient instability situation has been detected, appropriate emer-gency control strategies are triggered to minimize the impact of this on the safe operation of the network and reduce the possibility of a blackout. This thesis examines two differ-ent emergency control schemes: a) A fuzzy logic based emergency load and generator shedding scheme and b) A high voltage direct current (HVdc) power order reduction scheme based on synchronized phasors measurements. These strategies were developed for two power systems with contrasting characteristics: one for the Venezuelan power system which is a conventional power system completely based on alternating current (AC) transmission, and the other for the Manitoba Hydro network which heavily depend on long HVdc transmission for power transfer. The proposed wide area control systems demonstrated good performance on the Venezuelan and Manitoba Hydro power grids.

This thesis presents a novel technique for prediction of the transient stability status of a power system following a large disturbance such as a fault, and application of the tech-nique for subsequent emergency control. The prediction is made based on the synchro-nously measured samples of the magnitudes of fundamental frequency voltage phasors at major generation/load centers. The voltage samples are taken immediately after a fault is cleared and used as inputs to a binary classifier based on support vector machines to iden-tify the transient stability condition. The classifier is trained using examples of the post-fault recovery voltages (inputs) obtained through simulations and the corresponding sta-bility status (output) determined using a power angle-based stability index. Studies with the New England 39-bus test system indicate that the proposed algorithm can correctly recognize when the power system is approaching transient instability. The proposed sys-tem is then applied to Venezuelan power system and Manitoba Hydro power grid to demonstrate the applicability for large practical power systems. Performance of the pro-posed transient stability prediction scheme under the presence of asymmetrical faults, voltage sensitive loads, unlearned network topologies and measurement noise was found to be satisfactory. Once an impending transient instability situation has been detected, appropriate emer-gency control strategies are triggered to minimize the impact of this on the safe operation of the network and reduce the possibility of a blackout. This thesis examines two differ-ent emergency control schemes: a) A fuzzy logic based emergency load and generator shedding scheme and b) A high voltage direct current (HVdc) power order reduction scheme based on synchronized phasors measurements. These strategies were developed for two power systems with contrasting characteristics: one for the Venezuelan power system which is a conventional power system completely based on alternating current (AC) transmission, and the other for the Manitoba Hydro network which heavily depend on long HVdc transmission for power transfer. The proposed wide area control systems demonstrated good performance on the Venezuelan and Manitoba Hydro power grids.

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--Washington State University, May 2006. / Includes bibliographical references (p. 130-134).

Driven by economic, technical, and environmental reasons, the energy sector is moving into an era where large portions of increases in electrical energy demand will be met through widespread installation of distributed resources or what's known as distributed generation (DG). DG units can operate in parallel to the main grid or in a micro-grid mode. The later is formed by a cluster of DG units connected to a distribution network to maintain the reliability of critical loads, mainly when the grid supply is not available. Distributed resources include variable frequency sources, high frequency sources, and direct energy conversion sources producing dc voltages or currents. The majority of distributed resources are interfaced to the utility grid or to the customer load via dc-ac pulse-width-modulated (PWM) voltage source inverter (VSI) systems. However, these interfaces introduce new issues, such as the absence of the physical inertia, wide-band of dynamics, limited overload capability, susceptibility to parameters variation, and switching harmonics generation. In addition, the uncertain and dynamic nature of the distribution network challenges the stability and control effectiveness of a grid-connected inverter-based DG interface. Generally, difficulties appear in the form of grid impedance and interfacing parameter variations, fast and slow grid-voltage disturbances, grid distortion and unbalance, and interactions between the inverter ac-side filter and the grid. On the other hand, a micro-grid system will be dominated by inverter-based DG units. Unlike conventional power system generators, inverter-based DG units have no physical inertia. This fact makes the micro-grid system potentially susceptible to oscillations resulting from system disturbances. Severe and random disturbances might be initiated in a micro-grid system, due to load changes, the power sharing mechanism of the inverters and other generators, and interactions between the DG interface and the network. Motivated by the aforementioned difficulties, this thesis presents new control algorithms for the DG interface that guarantee stable and high power quality injection under the occurrence of network disturbances and uncertainties, in both the grid-connected and micro-grid systems. The control architecture of the proposed DG interface relies on the following subsystems. First, a newly designed deadbeat current regulation scheme is proposed. The proposed design guarantees high power quality current injection under the presence of different disturbing parameters such as grid voltage distortion, interfacing parameter variation, and inverter system delays. Further, it utilizes the maximum dynamic performance of the inverter in a way that provides a high bandwidth and decoupled control performance for the outer control loops. Different topologies of the ac-side filter are considered for the current control design. Second, a novel adaptive discrete-time grid-voltage sensorless interfacing scheme for DG inverters is proposed. The adaptive interface relies on a new interface-monitoring unit that is developed to facilitate accurate and fast estimation of the interfacing impedance parameters and the grid voltage vector (magnitude and position) at the point of common coupling. The estimated grid voltage is utilized to realize a grid-voltage sensorless interfacing scheme, whereas the interfacing parameters are utilized for the self-tuning control and interface-parameter monitoring. Further, a simple and robust synchronization algorithm and a voltage-sensorless average power control loop are proposed to realize an adaptive voltage-sensorless DG interface. The voltage-sensorless interface positively contributes to the elimination of the residual negative sequence and voltage feed-forward compensation errors, and to the robustness of the power sharing mechanism in paralleled inverter systems, where the power-sharing mechanism is generally based on open-loop controllers. Third, a new voltage control scheme for the DG interface featuring fast load voltage regulation and effective mitigation of fast voltage disturbances is proposed. The proposed voltage control scheme targets the problem of fast and large-signal-based voltage disturbances, which is common in typical distribution feeders. A hybrid voltage controller combining a linear with a variable-structure-control element is proposed for the DG interface. Positive and dual-sequence versions of the proposed voltage controller are developed to address the issue of unbalanced voltage disturbances. The proposed voltage controller successfully embeds a wide band of frequency modes through an equivalent internal model. Subsequently, wide range of balanced and unbalanced voltage perturbations, including capacitor-switching disturbances, can be effectively mitigated. Fourth, to constrain the drift of the low frequency modes in a conventional droop-controlled micro-grid, a new transient-based droop controller with adaptive transient-gains is proposed. The proposed power-sharing controller offers an active damping feature that is designed to preserve the dynamic performance and stability of each inverter unit at different loading conditions. Unlike conventional droop controllers, the proposed droop controller yields two-degree of freedom tunable controller. Subsequently, the dynamic performance of the power-sharing mechanism can be adjusted, without affecting the static droop gain, to damp the oscillatory modes of the power-sharing controller. The overall robust DG interface facilitates a robust micro-grid operation and safe plug-and-play integration of DG units on existing distribution systems; hence increasing the system penetration of DG. The direct result of this development is huge financial saving for utilities by capturing the salient features of deploying DG into existing utility networks. Further, these developments are significant to the industry as they provide the blue print for reliable control algorithms in future DG units, which are expected to operate under challenging system conditions.

Driven by economic, technical, and environmental reasons, the energy sector is moving into an era where large portions of increases in electrical energy demand will be met through widespread installation of distributed resources or what's known as distributed generation (DG). DG units can operate in parallel to the main grid or in a micro-grid mode. The later is formed by a cluster of DG units connected to a distribution network to maintain the reliability of critical loads, mainly when the grid supply is not available. Distributed resources include variable frequency sources, high frequency sources, and direct energy conversion sources producing dc voltages or currents. The majority of distributed resources are interfaced to the utility grid or to the customer load via dc-ac pulse-width-modulated (PWM) voltage source inverter (VSI) systems. However, these interfaces introduce new issues, such as the absence of the physical inertia, wide-band of dynamics, limited overload capability, susceptibility to parameters variation, and switching harmonics generation. In addition, the uncertain and dynamic nature of the distribution network challenges the stability and control effectiveness of a grid-connected inverter-based DG interface. Generally, difficulties appear in the form of grid impedance and interfacing parameter variations, fast and slow grid-voltage disturbances, grid distortion and unbalance, and interactions between the inverter ac-side filter and the grid. On the other hand, a micro-grid system will be dominated by inverter-based DG units. Unlike conventional power system generators, inverter-based DG units have no physical inertia. This fact makes the micro-grid system potentially susceptible to oscillations resulting from system disturbances. Severe and random disturbances might be initiated in a micro-grid system, due to load changes, the power sharing mechanism of the inverters and other generators, and interactions between the DG interface and the network. Motivated by the aforementioned difficulties, this thesis presents new control algorithms for the DG interface that guarantee stable and high power quality injection under the occurrence of network disturbances and uncertainties, in both the grid-connected and micro-grid systems. The control architecture of the proposed DG interface relies on the following subsystems. First, a newly designed deadbeat current regulation scheme is proposed. The proposed design guarantees high power quality current injection under the presence of different disturbing parameters such as grid voltage distortion, interfacing parameter variation, and inverter system delays. Further, it utilizes the maximum dynamic performance of the inverter in a way that provides a high bandwidth and decoupled control performance for the outer control loops. Different topologies of the ac-side filter are considered for the current control design. Second, a novel adaptive discrete-time grid-voltage sensorless interfacing scheme for DG inverters is proposed. The adaptive interface relies on a new interface-monitoring unit that is developed to facilitate accurate and fast estimation of the interfacing impedance parameters and the grid voltage vector (magnitude and position) at the point of common coupling. The estimated grid voltage is utilized to realize a grid-voltage sensorless interfacing scheme, whereas the interfacing parameters are utilized for the self-tuning control and interface-parameter monitoring. Further, a simple and robust synchronization algorithm and a voltage-sensorless average power control loop are proposed to realize an adaptive voltage-sensorless DG interface. The voltage-sensorless interface positively contributes to the elimination of the residual negative sequence and voltage feed-forward compensation errors, and to the robustness of the power sharing mechanism in paralleled inverter systems, where the power-sharing mechanism is generally based on open-loop controllers. Third, a new voltage control scheme for the DG interface featuring fast load voltage regulation and effective mitigation of fast voltage disturbances is proposed. The proposed voltage control scheme targets the problem of fast and large-signal-based voltage disturbances, which is common in typical distribution feeders. A hybrid voltage controller combining a linear with a variable-structure-control element is proposed for the DG interface. Positive and dual-sequence versions of the proposed voltage controller are developed to address the issue of unbalanced voltage disturbances. The proposed voltage controller successfully embeds a wide band of frequency modes through an equivalent internal model. Subsequently, wide range of balanced and unbalanced voltage perturbations, including capacitor-switching disturbances, can be effectively mitigated. Fourth, to constrain the drift of the low frequency modes in a conventional droop-controlled micro-grid, a new transient-based droop controller with adaptive transient-gains is proposed. The proposed power-sharing controller offers an active damping feature that is designed to preserve the dynamic performance and stability of each inverter unit at different loading conditions. Unlike conventional droop controllers, the proposed droop controller yields two-degree of freedom tunable controller. Subsequently, the dynamic performance of the power-sharing mechanism can be adjusted, without affecting the static droop gain, to damp the oscillatory modes of the power-sharing controller. The overall robust DG interface facilitates a robust micro-grid operation and safe plug-and-play integration of DG units on existing distribution systems; hence increasing the system penetration of DG. The direct result of this development is huge financial saving for utilities by capturing the salient features of deploying DG into existing utility networks. Further, these developments are significant to the industry as they provide the blue print for reliable control algorithms in future DG units, which are expected to operate under challenging system conditions.

Thesis--Ph. D., University of Hong Kong. / Mimeographed.

The notion of airplane stability and control being a balancing act between stability and control has been around as long as aeronautics. The Wright brothers’ first successful flights were born of the debate, and were successful at least in part because they spent considerable time teaching themselves how to control their otherwise unstable airplane. This thesis covers four aspects of handling for large transport aircraft: large size and the accompanying low frequency dynamics, the way in which lifting surfaces and control system elements are modelled in flight dynamics analyses, the cockpit feel characteristics and details of how pilots interact with them, and the dynamic instability associated with Pilot Induced Oscillations. The dynamics associated with large transport aircraft are reviewed from the perspective of pilot-in-the-loop handling qualities, including the effects of relaxing static stability in pursuit of performance. Areas in which current design requirements are incomplete are highlighted. Issues with modelling of dynamic elements which are between the pilot’s fingers and the airplane response are illuminated and recommendations are made. Cockpit feel characteristics are examined in detail, in particular, the nonlinear elements of friction and breakout forces. Three piloted simulation experiments are described and the results reviewed. Each was very different in nature, and all were designed to evaluate linear and nonlinear elements of the cockpit feel characteristics from the pilot’s point of view. These included understanding the pilot’s ability to precisely control the manipulator itself, the pilot’s ability to command the flight path, and neuro-muscular modelling to gain a deeper understanding of the range of characteristics pilots can adapt to and why. Based on the data collected and analyzed, conclusions are drawn and recommendations are made. Finally, a novel and unique PIO prediction criterion is developed, which is based on control-theoretic constructs. This criterion identifies unique signatures in the dynamic response of the airplane to predict the onset of instability.

Context: Despite an association between foot structure and the incidence of lower limb injury in sport, few studies have measured the effects of neutral, pronated and supinated foot structures during dynamic activity. Furthermore, despite its widespread use as an injury prevention method, the effects of athletic taping on individuals with pronated and supinated foot structures are unclear. Objectives: To explore whether individuals with pronated and supinated foot structures have poorer lower limb neuromuscular control as measured by postural stability and muscle reaction time in comparison to those with neutral feet. Additionally, the effects of athletic taping on individuals with neutral, pronated and supinated foot structures on aspects of lower limb neuromuscular control are also examined. Subjects: All subjects used in this thesis were aged from 18 – 30 years and took part in at least two hours of exercise each week. Subjects were categorised in to groups according to navicular drop height measures; neutral 5 – 9 mm; pronated ≥ 10 mm; supinated ≤ 4 mm. Methods: Neuromuscular control was analysed in subjects with neutral, pronated and supinated feet using dynamic postural stability and muscular reaction time measures. These measures were then repeated with four athletic taping conditions (arch tape, ankle tape, proprioceptive tape and no-tape) both before and after a period of exercise. Results: Individuals with pronated and supinated foot structures were shown to have reduced postural stability in comparison to those with neutral foot structures during some dynamic tasks. Pronated and supinated foot structures also resulted in slower muscle reaction times in comparison to those with neutral feet during a tilt platform perturbation. No differences were identified between dominant and non-dominant limbs on subjects with neutral, pronated or supinated foot structures; however the high incidence of foot structure asymmetry did appear to result in differences between contralateral limbs in both postural stability and reaction time parameters. Arch and ankle taping resulted in increased neuromuscular control after application, yet these effects diminished after a period of exercise. Conclusions: The results of this thesis provide evidence to suggest that foot structure does affect lower limb neuromuscular control as measured by postural stability and muscle reaction time. In addition athletic taping has been shown to affect neuromuscular control on subjects with neutral, pronated and supinated foot structures both before and after exercise. These findings may have wide implications in sport where individuals with pronated and supinated feet may be more susceptible to injury in comparison to those with neutral feet.

Thesis (M. Ed.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 27-31).