Abstract:
This thesis introduces a Brushless Doubly-Fed Machine (BDFM), stand-alone
generator system. Development of a BDFM current-forced model, along with the
analysis of air gap power distribution between the two stator windings and the rotor
circuit, pave the way for the characterization and analysis of stand-alone generator
systems.
The main disadvantage of the conventional diesel-driven generators viz., the
frequency regulation through the prime mover system, can be eliminated by using
doubly-fed generators, where the frequency of the ac excitation provides a means of
controlling the generator output frequency electrically. This facilitates the regulation
of both the generator terminal quantities (Voltage and Frequency) through the generator
unit itself, thus making the prime mover governor system cheaper and of less
importance. When compared with converter-based generator systems, the focus of
comparison shifts towards the economic viability since the converter-based system
dynamic responses can be comparable with a BDFM generator system.
For dynamic analysis, this work assumes a diesel engine as the prime mover.
A permanent speed-droop governor is assumed to prove the versatility of a BDFM
stand-alone generator. The stand-alone system is characterized by a seventh order
system, by assuming passive electrical load at the generator terminals.
The steady-state characteristics of the BDFM stand-alone generator system, both
simulation and experimental results, are discussed. A case study is presented in
evaluating the converter rating for a 100kW system and it is shown that BDFM standalone
generator operation about the synchronous speed results in a fractional converter
rating. A brief discussion on system component sizing is presented.
To facilitate the dynamic control and stability studies, linearized models of the
BDFM stand-alone generator are derived. These models can be used even with a prime
mover other than the diesel engine. The results of the studies showing the effect of
generator loading on the system eigenvalues are given.
Simulated dynamic characteristics of the BDFM stand-alone generator system,
under closed-loop control, are presented. The conventional proportional-integral (P1)
as well as the modern fuzzy control methods are used in obtaining the system dynamic
responses. It is observed that the BDFM dynamic characteristics are superior to those
of the conventional stand-alone generator systems.
Finally, experimental results obtained by using a laboratory, prototype BDFM
are included. A shunt connected DC machine drive is used as the prime mover and the
results show satisfactory dynamic responses of the generator terminal quantities, both
under startup and sudden load changes.
