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|Title: ||Architecture and control of large power networks with distributed generation|
|Authors: ||Garlick, William G.|
|Issue Date: ||2009|
|Publisher: ||© William George Garlick|
|Abstract: ||The architecture of the UK's passive power network has taken over one hundred years to
evolve through a process of demand and technology led development. In the early years of
electrical power, distribution systems were islands of distributed generation, often of
different voltages and frequencies. Increasing demand for electrical power and the need to
reduce distribution costs eventually led to the standardisation of frequency and voltages
and to the connection of the island systems into a large network. Today's power networks
are characterised by their rigid hierarchical structure and unidirectional power flows.
The threat of climate change is driving the demand for the use of more renewable energy.
For electricity production, this is achieved through generation using more wind, biomass,
tidal and solar energy. This type of generation is often referred to as Distributed
Generation (DG) because it is not a centralised facility connected to the high voltage
transmission grid but a distributed source connected to the lower voltage distribution
network. The connection of DG to the distribution network significantly alters the power
flow throughout the network, and costly network reinforcement is often necessary. The
advancement in the control of electrical power has largely been facilitated by the
development of semiconductor power electronic devices and has led to the application of
"Flexible Alternating Current Transmission Systems (FACTS), which include such devices
as "Static Var Compensators" (SVC) and Static Compensators (STATCOM), for the
control of network voltages and power flows.
Providing a secure power network is a demanding task, but as network complexity is
expected to grow with the connection of high levels of DG, so the problem of integration,
not just connection, of each successive generator becomes more protracted. A fundamental
change to the network architecture may eventually become necessary, and a new, more
active network architecture, perhaps based on power cells containing local generation,
energy storage and loads, has been proposed by some researchers.
The results of an historic review of the growth of power networks, largely in the UK, forms
the basis of a case to replace the conventional power transformer with an Active
Transformer that will provide a more controllable, flexible and robust DG connection and
will facilitate greater network management and business opportunities, and new power
flow control features.
The Active Transformer design is based on an a.c. link system and an a.c.-a.c. highfrequency
direct resonant converter. This thesis describes a model of the converter, built in
MATLAB and Simulink®, and used to explore control of the converters. The converter
model was then used to construct a model of the Active Transformer, consisting of a
resonant, supply-side converter, a high frequency transformer and a resonant, load-side
converter. This was then used to demonstrate control of bi-directional power flow and
power factor control at the Grid and Distribution Network connections.
Issues of robustness and sensitivity to parameter change are discussed, both for the
uncompensated and compensated converters used in the Active Transformer. The
application of robust H∞ control scheme proposed and compared to a current PI control
scheme to prove its efficacy.|
|Description: ||A Doctoral Thesis submitted in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Electronic, Electrical and Systems Engineering)|
PhD Theses (Control Systems Group)
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