1
5
Introduction
•
The
rotational
symmetry
of
electrical machines
and
(with
most
motors)
the
smooth
torque
results in quiet operation with little vibrations. Since
there are no elevated
tem
per
atures causing
material
fatigue, long
operating
life
can
be
expected.
• Electrical motors
are
built
in a variety of designs
to
make
them
compatible
with
the
load;
they
may
be foot- or fiange-mounted,
or
the
motor
may
have
an
outer
rotor
etc. Machine-tools which formerly
had
a single drive
s
haft
and
complicated mechanical internal gearing can now
be
driven by
a
multitude
of individually controlled motors producing
the
mechanical
power exactly where, when
and
in
what
form
it
is needed.
This
has removed
constraints
from machine tool designers.
III
special cases, such as machine-tools
or
the
propulsion
of
tracked vehicles,
linear elec
tric
drives are also available.
I
Signallevel I Power levei
-+-
I
Voltages,
currents
Torque, acceleration, speed, angular position etc
~
Signal acquisition:
Reconstruction
of
unmeasurable quantities, A
Elimination
of
sensors
Contrai:
Oecoupling, feed - forward, limiting
Coordination:
Coordinate transformation
.c
.-=:
Identification:
Estimation
of
variable parameters
Se
lf
tuning:
Computer aided commissioning
~
A daptation: Adjustment
of
contrai parameters
Optimisation: Minimisation
of
objective functions
Fig.
0.4.
Digital control
structure
of an electrical drive
1\
s wou
lei
Iw
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p
c
cted
,
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a
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ges
of
electric drives which lirnit or preclude
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Introdu
c
tion
or
turbine,
fuel-
or
solar cells).
The
lack
of
a suitable storage
battery
has
so far prevented
the
wide-spread use
of
electric vehicles.
The
weight
of
a
present
day
lead-acid
battery
is
about
50 times
that
of
a liquid fuel
tank
storing
equal energy, even when taking
the
low efficiency
of
the
combustion
engine into account.
• Due
to
the
magnetic
saturation
of
iron
and
cooling problems, electric mo-
tors
are
likely to have a lower power-to--weight
ratio
than,
for instance, high
pressure hydraulic drives
that
utilise
normal
instead
of
tangential
forces.
This is
of
importance
with servo drives on-board vehicles, e.g. for position-
ing
the
control surfaces of aircraft.
The
electromechanical energy conversion in controlled drives is
subject
to
the
terminal
quantities
of
the
electrical machine which can
be
changed
with
low losses by controllable power electronic converters consisting
of
semicon-
ductor
switches;
they
can produce voltages
and
currents
of
almost
any
wave-
form as prescribed by control which
today
is executed by microelectronic
components.
Thus
semiconductor technology, combining power conversion
and
high speed signal processing
at
reasonable cost, has been
the
essential
force
behind
the
development of todays high performance drives; this is
part
of
the
general
transition
from analogue
to
digital control systems using mi-
crocomputers
and
signalprocessors. Fig. 0.4 gives
an
impression
of
how
the
mechanical, power electronic
and
control functions, combining hardware
and
software, are interleaved in a
modern
drive system.