Browsing by Author "Layman, John W."
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- Analysis, monitoring and control of voltage stability in electric power systemsBegovic, Miroslav M. (Virginia Polytechnic Institute and State University, 1989)The work presented in this text concentrates on three aspects of voltage stability studies: analysis and determination of suitable proximity indicators, design of an effective real-time monitoring system, and determination of appropriate emergency control techniques. A simulation model of voltage collapse was built as analytical tool on 39-bus, 10-generator power system model. Voltage collapse was modeled as a saddle-node bifurcation of the system dynamic model reached by increasing the system loading. Suitable indicators for real-time monitoring were found to be the minimum singular value of power flow Jacobian matrix and generated reactive powers. A study of possibilities for reducing the number of measurements of voltage phasors needed for voltage stability monitoring was also made. The idea of load bus coherency with respect to voltage dynamics was introduced. An algorithm was presented which determines the coherent clusters of load buses in a power system based on an arbitrary criterion function, and the analysis completed with two proposed coherency criteria. Very good agreement was obtained by simulation between the results based on accurate and approximate measurements of the state vector. An algorithm was presented for identification of critical sets of loads in a voltage unstable power system, defined as a subset of loads whose changes have the most pronounced effect on the changes of minimum singular value of load flow Jacobian or generated reactive powers. Effects of load shedding of critical loads were investigated by simulation and favorable results obtained. An investigation was also done by sensitivity analysis of proximity indicators of the effects that locations and amounts of static var compensation have on the stability margin of the system. Static compensation was found to be of limited help when voltage instabilities due to heavy system loading occur in power systems. The feasibility of implementation of the analyses and algorithms presented in this text relies on development of a feasible integrated monitoring and control hardware. The phasor measurement system which was designed at Virginia Polytechnic institute and State University represents an excellent candidate for implementation of real-time monitoring and control procedures.
- Halphen's theorem and related resultsCulbertson, George Edward (Virginia Tech, 1970-03-05)Halphen's Theorem states that, "A necessary and sufficient condition for every dynamical trajectory in a positional field of force in E3 to be planar is that the field of force is either parallel or central." This result has been known for some time, however only the sufficiency part of the theorem is widely documented. A new analytic proof of the necessity part of Halphen's Theorem was developed. The details of this proof motivated the new concepts of a flat point in a field of force and a flat point on a dynamical trajectory in a positional field of force.
- Protection system representation in the Electromagnetic Transients ProgramChaudhary, Arvind K. S. (Virginia Tech, 1991-10-11)This work concerns the addition of the few critical elements of a protection system to the Electromagnetic Transients Program (EMTP). The EMTP is one of the most widely used programs for the simulation of transients in power systems. The EMTP contains models for almost every major power system component. A protection system consists of instrument transformers, relays, and circuit breakers. Models for current transformers and capacitor voltage transformers are developed, validated, and incorporated in EPRI/DCG EMTP Version 2.0. The user can define the values of the current transformer and capacitor voltage transformer parameters. Total Fortran capability has been added to EMTP; new subroutines and an inbuilt structure to allow the linking of user defined Fortran subroutines with the main EMTP are explained. This capability is necessary to simulate computer relay algorithms. The outputs of the algorithms can be passed to the EMTP, which enables the study of the dynamic interaction between the power system and the protection system. Models of specific relays for line protection (SLY12C) and transformer differential protection (BDD15B) are also available. The relay models can be used with different settings. These new features in EMTP together constitute the critical elements of a protection system. Thus, it is now possible to simulate the dynamic interactions between a power system and a protection system.
- Small signal analysis of nonlinear systems with periodic operating trajectoriesGroves, James O. (Virginia Tech, 1995-04-05)A new method for small-signal analysis of switching power converters is developed and implemented in a computer program. The method is derived for systems where the nonlinearities can be described by elements that can take on one of two values, based upon a controlling variable. Another requirement is that the system be periodic. The method is shown by examples to be very accurate, even at high frequencies. It predicts the subharmonic oscillation that can occur in converters with constant-frequency current-mode control. It is implemented using the COSMIR program to solve for the state equations and for steady-state, making a general power supply simulation program.
- Vector controlled induction motor drive systemsBharadwaj, Aravind S. (Virginia Tech, 1993-02-18)Over the years, dc motors have been widely used for variable speed drives for numerous industrial applications despite the fact that ac machines are robust, less expensive, and have low inertia rotors. The main disadvantage of the ac machines is the complexity in control and the cost of the related circuitry. With the advent of vector control, ac machines have overcome this disadvantage and are being employed in different applications where dc motors were traditionally used. The d-q modeling, simulation and analysis of the different vector control strategies are presented with the results for different configurations of the drive system. A Computer Aided Engineering (CAE) package has been developed to serve as a modeling tool for the entire drive system including the motor, converter, controller and the load. This package provides a user friendly environment to perform an interactive dynamic simulation to assess the torque ripple, losses, efficiency, torque, speed, and position responses and their bandwidth and evaluates the suitability of the drive system for a particular application. By utilizing the similarity between the vector controlled induction motor drive and the separately excited dc motor, a method for the design and study of the speed controller for the speed/position drive is formulated. This results in the simplicity of the design approach and helps in improving the performance of the drive system. Finally, a novel sensorless vector control scheme which eliminates the position transducer is formulated. The only input for this control scheme is the stator current measured by current transducers. The modeling, simulation and analysis for the different schemes is performed using the CAE package and experimental verification is performed with the aid of a DSP based drive system.