Control and Design of a High voltage Solid State Transformer and its Integration with
Renewable Energy Resources and Microgrid System
by
Xu She
A dissertation submitted to the Graduate Faculty of
North Carolina State University
in partial fulfillment of the
requirements for the degree of
Doctor of Philosophy
Electric Engineering-2013
BIOGRAPHY
Xu She was born in Hunan, China. He received the B.S. degree in electrical engineering
(major) and B.A. degree in English (minor), with honor from Huazhong University of
Science and Technology, China, in 2007. He received his M.S. degree majored in power
electronics and motor drive with honor from the same university in 2009. He started to
pursue his Ph.D. degree in North Carolina State University in 2009.
From August 2009 to July 2010, he has been working on the modeling of the green energy
hub and DC microgrid project. Since August 2010, he has been working on the solid state
transformer project. He was the team leader of Solid State Transformer (SST) group and
Medium Voltage DC (MVDC) transmission group at Future Renewable Electric Energy
Delivery and Management (FREEDM) Systems Center. From May to August 2012, he was
an intern with high power conversion systems laboratory at GE global research center, US,
conducting research on next generation high voltage dc transmission (HVDC) system.
His research interests are high power/voltage converters and their industrial applications,
and renewable energy resources integration.
His role in the first job will be a research engineer (lead professional career band) in high
power conversion systems laboratory at GE global research center.
Chapter
1 Introduction
1.1 The distribution transformer
1.1.1 Introduction of the distribution transformer
Power generation, transmission, and distribution are the three main constituents of the
modern power system, in which the transformer plays a most critical role [1]. Transformers
enable high efficiency and long distance power transmission by boosting the voltage to a
higher one in the generation side with the so called power transformer. In the distribution
system side, this high voltage is stepped down for industrial, commercial, and residential use
with the so called distribution transformer.
The distribution transformer provides final voltage transformation to the end users in the
distribution system, which usually with voltage level less than 34.5kV at high voltage side.
At the low voltage side, 120/240V split single phase system and 480V three phase systems
are usually adopted in the US.
The distribution transformer can be classified from different perspective of view. According
to the phase number, it can be classified into three phase transformer and single phase
transformer. According to the installation method, it can be classified into pole mounted
transformer and pad mounted transformer. The pad mounted transformers are installed for
the distribution system with lines located at ground level or underground. While the pole
mounted transformers are mounted on a utility pole. According to the insulation medium, it
can be classified into liquid-immersed transformer and dry type transformer.
The distribution transformers are widely used in various applications, such as renewable
energy resources integration, high power charge station, traction system, reactive power
compensator, active power filter, and etc., as shown in Figure 1-1[2][3]. It functions as a
passive interface between the distribution system and the low voltage loads/sources.
Therefore, the voltage quality of the grid cannot be guaranteed if no additionally devices are
installed.
LINK:
https://repository.lib.ncsu.edu/bitstream/handle/1840.16/9027/etd.pdf?sequence=1&isAllowed=y
