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Abstract
The world is rapidly changing from using the fossil based energy, which is facing
exhaustion and having a lot of environmental issues, to the use of renewable energy
sources such as sun energy and wind energy. Energy from the sun has become an
important source for terrestrial applications and remains the prime source of energy
in nonterrestrial applications such as those in skyexplorers. However, a renewable
energy source is expensive, bulky, and its performance is weather dependent, which
make testing of downstream converters very difficult. As a result, a nonlinear source
emulator (NSE) is a good solution to solve the problems associated with the use of
real nonlinear sources in testing phases.
However, a recent technical survey conducted during this work shows that most
existing NSEs have only been concerned with simulating nonlinear systems in terrestrial
applications. Furthermore, their dynamic performance were not fast enough
in order to imitate how a real nonlinear energy source would react under extreme
conditions and operation modes. Particularly, a system in the sky can experience
a step change of sunlight irradiation. Moreover, operation modes may include
load step between nominal and open circuit, and load step between nominal and
short circuit. Under these conditions, a practical nonlinear source system will react
almost instantly, whereas the fastest among existing NSEs had a transient of about
3 milliseconds.
It is the highlight of this thesis, to demonstrate the development of a proposed
NSE system with high dynamic performance. The goal of the work is to achieve a
stateofthe art transient time of 10 µs. In order to produce the arbitrary nonlinear
curve, the exponential function of a typical diode is used, but the diode can be
replaced by other nonlinear curve reference generator unit.
Because nonlinear energy sources come in different sizes and power rating, a single
NSE may not be sufficient to simulate a wide selection of nonlinear sources. For this
reason, the proposed NSE system is realized as modules. Stacking or connecting
multiple modules in parallel will allow simulation of nonlinear source systems with
higher output power.
In this work, a module will consist of two fundamental units: an isolated power
supply and an NSE. The isolated power supply has to possess a very low circuit
inputtooutput capacitance (very low Cio) in order to reduce the effect of conductive
commonmode current produced by the high rate of change of voltage over
time (high dv/dt) at the NSE output.
v/xvii
The contributions of the thesis are based on the development of both units: the
low Cio isolated power supply and the high dynamic performance NSE. Both units
are investigated theoretically and experimentally.
For the very low Cio power supply, we propose a new topology and control, together
with a novel transformer structure, in which, its two windings are separated by a
significant distance, in order to attain a low interwinding capacitance. A mathematical
model is proposed to accurately model the interwinding capacitance of the
proposed transformer. The result achieved is a total converter Cio of 10 pF in a
300W prototype, which is 30 times lower than that of existing approaches.
For the NSE, we propose a new circuit consists of an ultrafast tracking converter and
a novel nonlinear curve reference generator based on diode curve. Even though the
nonlinear curve is based on diode pn junction, the proposed NSE can simulate other
arbitrary nonlinear sources if the diode is replaced by other appropriate nonlinear
curve reference generator units. The prototype is 200W rating. The experimental
results show that the proposed NSE can react to a fast change in input source (such
as an abrupt change of wind speed for wind turbine emulator), as well as to a load
step from nominal to open circuit and vice versa, all within 10 µs.
The proposed NSE, therefore, offers the stateoftheart dynamic performance among
devices of the same kind. It also offers a complete solution for simulation of nonlinear
source systems of different sizes, both in terrestrial and nonterrestrial applications.
Key words: Current transformers, dcdc power converters, hysteresis,
parasitic capacitance, system, stacking, switching converters.
Original language  English 

Publisher  Technical University of Denmark, Department of Electrical Engineering 

Number of pages  168 
Publication status  Published  2015 
Keywords
 Current transformers
 dcdc power converters
 hysteresis
 Parasitic capacitance
 PV system
 Stacking
 Switching converters
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Projects
 1 Finished

High Performance Solar Array Simulator
NguyenDuy, K., Andersen, M. A. E., Knott, A., Zhang, Z., Wolf, C. & Kyyrä, J.
Technical University of Denmark
01/12/2011 → 07/05/2015
Project: PhD