Title page for ETD etd-05182011-093430


Type of Document Dissertation
Author Ahmed, Sara Mohamed
Author's Email Address sahassan@vt.edu
URN etd-05182011-093430
Title Modeling of Power Electronics Distribution Systems with Low-frequency, Large-signal (LFLS) Models
Degree PhD
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Boroyevich, Dushan Committee Chair
Lindner, Douglas K. Committee Member
Mattavelli, Paolo Committee Member
Ragab, Saad A. Committee Member
Wang, Fei Fred Committee Member
Keywords
  • Low frequency large signal models
  • impedance
  • small-signal model
  • Modeling
  • average models
Date of Defense 2011-04-29
Availability unrestricted
Abstract
This work presents a modeling methodology that uses new types of models called low-frequency, large-signal models in a circuit simulator (Saber) to model a complex hybrid ac/dc power electronics system. The new achievement in this work is being able to model the different components as circuit-based models and to capture some of the large-signal phenomena, for example, real transient behavior of the system such as startup, inrush current and power flow directionality. In addition, models are capable of predicting most low frequency harmonics only seen in real switching detailed models. Therefore the new models system can be used to predict steady state performance, harmonics, stability and transients. This work discusses the modeling issues faced based on the author recent experiences both on component level and system level. In addition, it recommends proper solutions to these issues verified with simulations.

This work also presents one of the new models in detail, a voltage source inverter (VSI), and explains how the model can be modified to capture low frequency harmonics that are usually phenomena modeled only with switching models. The process of implementing these different phenomena is discussed and the model is then validated by comparing the results of the proposed low frequency large signal (LFLS) model to a complete detailed switching model. In addition, experimental results are also obtained with a 2 kW voltage source inverter prototype to validate the proposed improved average model (LFLS model). In addition, a complete Verification, Validation, and Uncertainty Quantification (VV&UQ) procedures is applied to a two-level boost rectifier. The goal of this validation process is the improvement of the modeling procedure for power electronics systems, and the full assessment of the boost rectifier model predictive capabilities. Finally, the performance of the new models system is compared with the detailed switching models system. The LFLS models result in huge cut in simulation time (about 10 times difference) and also the ability to use large time step with the LFLS system and still capture all the information needed. Even though this low frequency large signal (LFLS) models system has wider capabilities than ideal average models system, it still can’t predict all switching phenomena. Therefore, another benefit of this modeling approach is the ability to mix different types of models (low frequency large signal (LFLS) and detailed switching) based on the application study they are used for.

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