DYNAMIC MODELING
OF
GE
1.5
AND
3.6
MW WIND TURBINE-
GENERATORS FOR STABILITY SIMULATIONS
Nicholas
W.
Miller, Juan
J.
Sanchez-Gasca, William
W.
Price
Robert
W.
Delmerico
GE
Power Systems
GE
Research
Schenectady,
NY
Niskayuna,
NY
Abstract
-
GE Power Systems
has
an ongoing effort dedicated
to development of models of GE wind turbine generators
(WTG)
suitable for
use
in
system impact studies.
This
paper
documents the present recommendations for dynamic
modeling of the GE
1.5
and
3.6
MW
WTG
for
use
in system
impact studies.
The
paper includes recommended model
structure and data,
as
well the assumptions, capabilities and
limitations
of
the resulting model.
1.
Introduction
The goal of this effort is the development of
a
simple model
appropriate for bulk power system dynamic studies. It is
valuable to put the model limitations
in
the context
of
what
analysis is required. First and most important, this model is
for positive sequence phasor time-domain simulations, e.g.
PSLF
or
PSSle.
Second,
the
analysis is mainly focused on
how the wind turbine-generators
(WTGs)
react to
disturbances, e.g. faults, on
the
transmission system. Third,
the model provides for calculation
of
the effect of wind speed
fluctuation
on
the electrical output of the
WTG.
Details
of
the
device dynamics have been substantially simplified.
Specifically, the very fast dynamics associated with the
control of the generator converter have been modeled
as
algebraic (i.e. instantaneous) approximations
of
their response.
Representation of the turbine mechanical controls has been
simplified
as
well. The model is not intended for
use
in
short
circuit studies.
2.
Model Overview and
Philosophy
2.1
Fundamentals
A simple schematic of the GE Wind System is shown in
Figure
2-1.
The GE
WTG
generator is unusual from
a
system
simulation perspective. Physically, the machine is
a
relatively
conventional technology wound rotor induction (WRI)
machine. However, the key distinction is that this machine is
equipped with
a
solid-state AC excitation system. The AC
excitation is supplied through an ac-dc-ac converter. For the
GE
Power
Systems
Energy Consulting
IEEE
WTG Modeling
Panel
Session
July
2003
GE
3.6
MW
WTG
the converter is connected
as
shown
through
a
transformer at
a
lower voltage than the stator
winding.
For
the
GE
1.5
MW
WTG
the converter is
connected at the same volage
as
the stator winding. Machines
of this structure are termed 'double fed', and have
significantly different dynamic behavior than either
conventional synchronous
or
induction machines. Modeling
of
the
GE
1.5
and
3.6
machines with conventional dynamic
models for either synchronous
or
induction machines is, at
best, highly approximate and should be avoided.
T
Figure
2-1.
GE
WTG
Major Components.
The fundamental frequency electrical dynamic performance of
the GE
WTG
is completely dominated by the
field
converter.
Conventional aspects of generator performance related to
intemal angle, excitation voltage, and synchronism are largely
irrelevant. In practice, the electrical behavior of the generator
and converter
is
that of
a
current-regulated voltage source
inverter. Like other voltage
source
inverters (e.g.
a
BESS
or
a
STATCOM), the converter will make the
WTG
behave like
a
voltage behind
a
reactance that results in the desired active
and reactive current being delivered to the device terminals.
The rotation of the machine means that the ac frequency on
the rotor winding corresponds to the difference between the
stator frequency (60Hz) and the rotor speed. This is the slip
frequency of the machine. In the vicinity of rated power, the
GE
1.5
and 3.6 machines will normally operate at 120%
speed,
or
-20%
slip. Control of the excitation frequency
allows the rotor speed to be controlled over
a
wide range,
?30%.
The rotation
also
means that the active power is
divided between the stator and rotor circuits, roughly in
proportion to
the
slip frequency. For rotor speeds above
synchronous, the rotor active power is injected into the
network through the converter. The active power
on
the rotor
is converted to terminal frequency (60Hz),
as
shown
in
Figure
0-7803-7989-6/03/$17.00
02003
IEEE 1977