241 |
Energy conversion unit with optimized waveform generationSajadian, Sally January 2014 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / The substantial increase demand for electrical energy requires high efficient apparatus dealing with energy conversion. Several technologies have been suggested to implement power supplies with higher efficiency, such as multilevel and interleaved converters. This thesis proposes an energy conversion unit with an optimized number of output voltage levels per number of switches nL=nS. The proposed five-level four-switch per phase converter has nL=nS=5/4 which is by far the best relationship among the converters presented in technical literature. A comprehensive literature review on existing five-level converter topologies is done to compare the proposed topology with conventional multilevel converters. The most important characteristics of the proposed configuration are: (i) reduced number of semiconductor devices, while keeping a high number of levels at the output converter side, (ii) only one DC source without any need to balance capacitor voltages, (iii) high efficiency, (iv) there is no dead-time requirement for the converters operation, (v) leg isolation procedure with lower stress for the DC-link capacitor. Single-phase and three-phase version of the proposed converter is presented in this thesis. Details regarding the operation of the configuration and modulation strategy are presented, as well as the comparison between the proposed converter and the conventional ones. Simulated results are presented to validate the theoretical expectations. In addition a fault tolerant converter based on proposed topology for micro-grid systems is presented.
A hybrid pulse-width-modulation for the pre-fault operation and transition from the pre-fault to post-fault operation will be discussed. Selected steady-state and transient results are demonstrated to validate the theoretical modeling.
|
242 |
Changing from the silo model to the horizontal layers model in public policy regulations: the implications and potential for the telecommunications industrySpencer Logan, Lemuella C. 12 1900 (has links)
The end of the Twentieth Century and the start of the Twenty First Century has been a tumultuous time for the Telecommunications Industry. Even as it moves forward to embrace the new technologies the Industry finds itself embroiled in issues of governance. The Industry finds itself in a dilemma since innovations increase at a rate faster than the laws can be changed and these render its existing laws and policies to be in some cases obsolete and inappropriate for the reality of the present. In the past, the United States of America has relied on vertically integrated top down laws and methods of regulating all the different parts in its Telecommunications Industry. These laws are contained in the different numbered Titles of this Countrys Legal Codes. Since the inception of these laws, emphasis was placed in creating and documenting policies structured by industry, sector and type of content. This form of regulation is usually referred to as the Silo Method. However, in recent years, especially in the regulation of the Telephony industry, the method of law and rule formulation moved from content regulation to one in which the technologies are getting regulated in what has been described as a Layers Method. This paper first considered whether the Silo Method of regulation is in actuality the same as using the Horizontal Layers method and showed that this is the case. Then it determined that Enhanced Services are the same as Basic Services and that Telecommunications Services are the same as Information services and showed that given that the pair sets as noted were the same, it went on to conclude that all these services were essentially the same. While studying to some detail the technologies of VoIP, the paper also showed that VoIP although an Internet technology is similar to traditional telephony, and is both a Telecommunications Service and Information Service based on the definition as given in the law as well as the technologies that are used and that as a result of this, the current regulatory environment for this service with regards to telephony is inconsistent. It concluded that Telecommunications policies though now adequate may need to be modified.
|
Page generated in 0.0324 seconds