Academic literature on the topic 'LD5655.V856 1994.Y363'

The extended describing function method is proposed as a systematic small-signal modeling approach to nonlinear switching circuits. This method offers significant simplification upon the previous work on using the multi-variable describing functions to treat the circuit nonlinearities. As an extension to the statespace averaging method, this modeling technique can incorporate any Fourier components for good model accuracy and provides continuous-time small-signal models for PWM topologies and various soft-switching resonant topologies. The proposed method is demonstrated using four resonant topologies and two multi-resonant topologies. These circuits are strongly oscillatory, and thus they cannot be modeled by means of traditional averaging techniques. By employing the proposed modeling method, the dynamics of the resonant converters are analyzed with emphasis on the nonlinear interaction between the switching frequency and the circuit natural resonant frequency. Equivalent circuit models are provided for more convenience of practical designs. Small-signal analysis is also performed for two challenging multi-resonant topologies with complex structure and operation. All of the theoretical models are verified experimentally and the predictions are well supported by the measurement data up to the Nyquist frequency.
Ph. D.

SiC whisker reinforced (Ca_0.6,Mg_0.4)Zr₄(PO₄)₆ (CMZP) matrix composites containing 10, 20, and 30 vol % whiskers were produced using a glass encapsulated hot isostatic pressing (HIPing) technique. The best HIPing temperature, pressure, and time conditions to optimize composite density and strength were determined to be 1050°C, 103 MPa, and 0.25 h.
Ph. D.

As the power systems grow, system connections become more complex. Due to cost and environmental concern, more and more parallel lines and series compensated lines may be installed in the system. In order to efficiently use the transmission network, more nonlinear flexible devices such as the phase shifter and the advanced compensation system will be put into use. Once a fault occurs on such a system, a delay in clearing the fault is usually not permissive. This requires a new generation of relays which have high security and dependability and high operating speed. With the advent of high speed microprocessor and fiber optic communication technologies, it is possible to develop high performance relays. In this dissertation, a new generation of pilot relays and non-pilot relays were developed for a transmission line. The pilot relays include the instantaneous percentage current differential (IPD), the phase comparison and the phasor based percentage current differential (PPD) principles. In the pilot protections the synchronized phasor measurement techniques are employed and digital CT saturation detectors are incorporated. All these schemes in primary protections feature charging current (or shunt current ) compensation. The phasor based principles are designed to work within one and a half cycles; while others based on sample by sample comparison are assumed to work in less than a cycle. The non-pilot relays to be investigated in this dissertation include the fault location based and phase angle based directional distance relays. One cycle data window is used in the phasor calculation. Both the distance relays are assumed to make a trip decision in about one and a half cycles. All algorithms were simulated against different fault conditions using EMTP outputs. The simulation results show all the pilot relay algorithms work well for EHV IUHV transmission lines including the series compensated lines. The fault location based distance relay works well in most cases, but it may give a wrong decision for the close-in fault with the fault resistance and may have a singularity problem. The phase angle based distance relay works very well for different fault conditions and is insensitive to fault resistance. The modified phase angle based distance relay was also developed for the series compensated line. It would not lose the direction for faults with or without fault resistance, either for a compensated system in forward direction, or in an adjacent line in reverse direction. The overreach is within 20% of the protected zone. This relay algorithm is also based on the one-cycle data window DFT, and it can give a reliable trip decision in about two cycles. All pilot relays with a fiber optic link and the phase angle based distance relay can constitute a new generation of protection systems for EHV IUHV transmission lines.
Ph. D.

A microprocessor based bus protection scheme has been proposed for a single bus system which employs a new technique to overcome the problem of current transformer saturation. The protection scheme uses a combination of the percentage differential current principle and the phase comparison principle. A sampling rate of 1440 Hz is used. Existing algorithms for a saturation detector are reviewed and a new saturation detector has been developed. This new saturation detector employs the slope difference of the secondary current to determine the CT state. It has a high sensitivity and can reveal early (one-eighth cycle) saturation. With the incorporation of this new saturation detector, the bus relay can make a correct decision for either an internal or an external fault in the presence of current transformer saturation in a half cycle in most cases. The bus protection scheme has been coded in Fortran and tested against data produced from EMTP. The simulated results from eight sets of data are presented in this thesis. All cases show that the bus protection scheme works correctly. The algorithm for the new saturation detector will be implemented using a 32-bit microprocessor by Mr. Paul A. Dolloff.
Master of Science

Peak load estimation is a critical element in utility decision making. An electric utility must construct, maintain, and operate equipment sufficient to meet the peak, or maximum demand level. Electric utilities have utilized several methods of analyzing energy consumption which have yielded various levels of accuracy for estimating maximum demand. In this research, a new method, Nonlinear Load Research Estimation (NLRE), is proposed to estimate the peak load and load characteristics of individual and group of different customer classes. Load research data is used to develop KWHr-to-KW conversion factors, diversity factors, and average time-varying load data as a function of customer class, month, and type of day. Load research data is used to derive monthly load shapes by customer class. These profiles are used to apportion customer KWHr usage among billing cycles according to the split indicated by test data. This parsed KWHr can be further allocated based on type of day to estimate weekday and weekend peak values.
Ph. D.

In this paper, we consider the kinetic equation for a dense square-well fluid and the geometric factor Y _ 1, provide the related kinetic theory, and prove a global existence theorem in L1 for the kinetic equation under rather general initial value condition. An analogue of the classical H-theorem is verified.
Ph. D.