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Alternative Measurement Approach Using Inverse Scattering Theory to Improve Modeling of Rotating Machines in Ungrounded Shipboard Power Systems

Title: Alternative Measurement Approach Using Inverse Scattering Theory to Improve Modeling of Rotating Machines in Ungrounded Shipboard Power Systems.
Name(s): Breslend, Patrick Ryan, author
Edrington, Christopher S., 1968-, professor directing thesis
Graber, Lukas, 1976-, committee member
Steurer, Michael, committee member
Florida State University, degree granting institution
College of Engineering, degree granting college
Department of Electrical and Computer Engineering, degree granting department
Type of Resource: text
Genre: Text
Issuance: monographic
Date Issued: 2015
Publisher: Florida State University
Place of Publication: Tallahassee, Florida
Physical Form: computer
online resource
Extent: 1 online resource (92 pages)
Language(s): English
Abstract/Description: The Navy has proposed to use a shipboard power system operating at medium voltage direct current to distribute power for their all-electric ship. The power is generated by electric machines as alternating current and requires power electronic rectifiers to output direct current. Power electronics converters are needed to convert the direct current to alternating current for ship propulsion and service loads. An increase in the use of fast switching power electronics is expected in future ships. The increased voltage rise time on switches is known to produce unwanted high frequencies with corresponding wavelengths of the same order of magnitude as the length of the ship hull. These high frequency transients can cause the ship system to couple with the surrounding ship hull causing adverse effects. The amount of high frequency content and the impact it has on the ship system performance is difficult to calculate with current models. Increased voltage and performance requirements for power electronics has led to advancements in switching frequencies into the 10s to 100s of kilohertz and increased voltage edge rates. The faster switching corresponds to higher frequency responses from the shipboard power system. Research has shown that high frequency content in electrical power systems is responsible for parasitic coupling and ultimately damage to the equipment. Electric machines, for instance, have increased winding and iron losses, overvoltages at the terminals, and even bearing currents via shaft voltages. The Navy is interested in simulating ship systems to test their electromagnetic compatibility before implementing or committing to a specific design. There are numerous techniques used to acquire machine parameters that have been proven to be useful in modeling electric machine behavior. The approaches were considered by the amount of proprietary information needed to acquire accurate results, the complexity of the modeling methods, and the overall time it takes for implementation. A majority of system simulations gravitate towards simple solutions for machine behavior which require assumptions to be made that deviate from the actual machine behavior. Exact inner dimensions, winding layouts, end winding dimensions, insulation thickness, and other information are proprietary and often not accurate representations of the physical machine once built. It is time consuming to obtain an accurate working model when assumptions are made or when detailed computer aided design models are needed to calculate machine response quantities. The research modeling approach put forth in this paper is not aimed at capturing the steady-state behavior of the machine. It is shown that a detailed understanding of the motor may not be necessary to accurately model the high frequency effects. It is the transient behavior at non-operating frequencies that need to be modeled correctly to develop new models of shipboard power systems for grounding research. The frequency dependent information is most useful to determine frequencies of interest that other modeling techniques are less likely to capture and point out. Previously suggested measurement techniques have been considered useful in determining parameters of machines but are not always accurately implemented without in-depth knowledge of the motor that may be proprietary. Lumped-parameter models are based on extracting information at transitional frequencies or looking at the slope of a variable over a frequency range. These models tend to be over simplified representations of the component by averaging the parameters for given ranges. In reality a machine's impedance varies with all frequencies. Lumped parameter based models typically over simplify the grounding behavior of the machine by not varying the impedance as a function of frequency. The technique used in this research is based on scattering parameters, a way of determining the terminal behavior of the machine without the knowledge of the actual inner workings of the machine. The inverse scattering technique uses steady-state stimuli to calculate reflection and transmission coefficients of system components allowing the device to be considered as a black box. This can be understood as electrical snapshots of how the machine would respond when subjected to a range of spectral content. The approach could have a significant impact on the modeling of ground interactions with machines. The machine can now be measured and characterized with no prior knowledge of the machine. The measurements are placed in simulation software in the typical measurement configurations used in other approaches to extract parametric data. It was discovered that these different configuration setups could now be measured in software without the need to physically reconfigure the machine's wiring for each measurement. This modeling approach was coined 'virtual measurement modeling.' To the best of the author's knowledge there are not any known techniques for fast model prototyping of electric machines which cover a broad range of frequencies with high accuracy. This thesis will present a possible solution for consideration in future models developed for grounding studies. This approach outlines a promising technique that can be easily implemented with high accuracy and reproducibility. The technique was derived from inverse scattering theory and was implemented on electric machines for characterizing high frequency behaviors.
Identifier: FSU_2015fall_Breslend_fsu_0071N_12834 (IID)
Submitted Note: A Thesis submitted to the Department of Electrical & Computer Engineering in partial fulfillment of the requirements for the degree of Master of Science.
Degree Awarded: Fall Semester 2015.
Date of Defense: August 3, 2015.
Keywords: Electric Machines, Electromagnetic Interference, High Frequency, Scattering Parameters, Shipboard Power System, Transient
Bibliography Note: Includes bibliographical references.
Advisory Committee: Chris S. Edrington, Professor Directing Thesis; Lukas Graber, Committee Member; Mischa Steurer, Committee Member.
Subject(s): Electrical engineering
Persistent Link to This Record:
Owner Institution: FSU

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Breslend, P. R. (2015). Alternative Measurement Approach Using Inverse Scattering Theory to Improve Modeling of Rotating Machines in Ungrounded Shipboard Power Systems. Retrieved from