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constant frequency (VSCF) system for aircraft
applications. More accurately, it focuses on the design of
an output filter to reduce the influence of non-linear
loads. The VSCF system consists in a doubly fed
induction generator (DFIG) supplying a stand-alone
aircraft grid through its stator windings. It uses back-to
back PWM converters connected to the rotor for sub
and super synchronous speed operation. A permanent
magnet synchronous machine (PMSM) connected to a
variable speed prime mover supplies these converters.
An efficient control strategy of the system was presented
in a previous paper for linear loads. However, non
linear loads such as 6-pulse diode rectifiers, that can
represent up to 50(% of the total load introduce
undesirable current harmonic components. A LC output
filter is thus designed to eliminate them. Simulation
results demonstrate the feasibility of the proposed
system.
Index Terms--Doubly fed induction generator - LC
output filter - 6-pulse diode rectifier - stand-alone mode
- variable speed constant frequency system
I. INTRODUCTION
relatively limited speed range is used because only a
fraction of the generator output is required to drive the
svystem. The presented DFIG supplies energT through its
stator windings to a stand-alone aircraft grid. It uses back
to-back PWM converters connected to the rotor for sub and
super synchronous speed operation. A permanent magnet
synchronous machine connected to a variable speed prime
mover supplies these converters (Fig. 2). This system has
three main advantages. The first one is that the rating of the
power converters used in the rotor circuit is substantiallv
lower than the machine rating and is fixed by the range of
the operating speed [1. 2. 3, 4]. The second one is that we
can remove the hydraulic or mechanical svstem and thus
get rid of the maintenance costs. Finally, the system is fully
autonomous and there is no need of supply power from the
grid to drive the generator. In this study. the DFIG is of
50kVA and its synchronous speed N" is of 12000rpm. The
speed range varies from 0.6NS in sub svnchronism to 1.25N,
in super synchronism. The aircraft grid is regulated to
deliver RMS single-phase voltage of 115V at a constalnt
frequency of 400Hz. The DFIG is controlled to deliver
constant magnitude and frequency voltage independentlv of
the load conditions and the rotational speed of the prime
mover. It uses a vector control scheme based on a d-q
Doubly fed induction generators (DFIG) are receiving
renewed attention as sources of constant frequency
generators from variable speed movers [1.,3,10]. Nowadavs.
two systems are available on aircraft. The first one. called
CSD (constant speed drive) is a hydraulic or mechanical
system that converts a vanrable shaft speed from the engine,
to a constant shaft speed for the electrical synchronous
generator as in Fig. l.a. The major inconvenient of such a
system is its costly maintenance. The second one (Fig. l.b).
that can be classified as a VSCF solution. uses a
synchronous generator with power converters to produce a
constant frequency. A drawback of this solution is that the
converter tak-es into account the totality of the generator
output power [9]. Regarding VSCF solutions, the use of
Hydraulic or
Prime ~~mechanical SG
mover syIstem
AC/DC converter DC/AC converter
Fig. 1 Available systems on aircraft Fig. 2 Global scheme of the proposed VSCF system
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