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|Title: ||New approach to steady-state and dynamic nonlinear modelling of laminated salient-pole alternator systems|
|Authors: ||Abdel-Halim, Mohammed A-S.|
|Issue Date: ||1986|
|Publisher: ||© Mohammed A. Abdel-Halim|
|Abstract: ||A complete mathematical model for a generator system consisting of an
isolated laminated salient-pole alternator, exciter and prime mover is
presented, with emphasis on the inherent electromagnetic nonlinearities
in the alternator and its exciter.
An equivalent circuit, representing the rotor circuits accurately, has
been adopted to model the al ternator in the dqo reference frame. A
computer program has been developed to calculate the unsaturated
parameters of the model using the machine design data.
A new approach has been developed to account for the electromagnetic
saturation effects on the model reactances. Consequently new
saturation factors, based on the machine design particulars have been
deri ved. The advantages of these saturation factors, compared with
conventional factors, are that both mutual saturation effects between
the main and leakage fluxes, and between the direct- and quadratureaxis
fluxes are considered.
A mathematical nonlinear model, utilising the new saturation factors,
is presented for a system containing an isolated laminated salientpole
alternator and a direct thyristor static exciter. A digital
computer program has been developed to simulate the system. The
predicted results, for some steady state and dynamic candi tions, showgood
agreement with test results and clear improvement over those
obtained if saturation is either neglected or considered using the
conventional saturation factors.
At high saturation levels, the conventional method of calculating the
machine transformer voltages, using static saturated reactances, gives
unacceptable errors. A method for calculating these voltages
correctly, in models utilising the currents as state space variables,
is presented using new derived dynamic saturated reactances. This
dynamic reactance concept is presented in a generalised form so that it can be applied to any machine with different saturation factors.
The previous mathematical model of the alternator system has been
modified according to the dynamic reactance concept, and the computer
program has been developed accordingly. The predicted results confirm
the need to apply this concept especially to dynamic conditions
characterised by high saturation levels.
To extend the analysis to a wider range of loading conditions, the
alternator has been modelled in the abc reference frame. The
unsaturated, static and dynamic saturated reactances of the machine in
this reference frame have been obtained using conventional dqo-abc
transformation techniques. Starting from the fundamental machine
relations, a new set of equations, in the phase reference frame, has
been derived employing the new dynamic reactance concept.
A comprehensive system consisting of an isolated laminated salientpole
alternator, brushless exciter, thyristor divert automatic voltage
regulator and a diesel prime mover has been studied. Both the
alternator and the exciter have been modelled in the abc frame to
comply with the nature of rectifier loading associated with the
exci ter. A complete steady state and dynamic mathematical model is
presented where the t~r technique has been applied to the dynamic
variable topology of the system electrical circuits. The model
presented covers all the possible modes of operation associated with
the exciter rotating bridge rectifier circuit. A digital computer
program has been developed to simUlate the system. The predicted
results obtained using the new set of saturation factors in
conjunction with the dynamic reactance concept show good agreement
with the test results.
The study presented confirms the validity of the mathematical models
developed for the alternator systems. Also, it supports the metlxxi by
which the electromagnetic nonlinearity has been accounted for.|
|Description: ||A Doctoral |