Decentral Solutions - Design Guide
Modularization therefore requires the distribution of
intelligence to the individual sections and modules.
Sure, centralized installations can be modularized,
but then motor controls will be physically separated
from the rest of the module.
■Ready-installed intelligence
The function of machinery and applications is typically
tested at the suppliers. Machines are built, tested,
calibrated and taken apart for transportation.
The process of rebuilding the application at the
production site is considerably simplified by shipping
it in modules with built-in motor controls, as rewiring
and testing is time consuming and calls for skilled
personnel. Using ready-installed, decentralized
installations reduces both time and risk as wiring for
motor, control and sensors are already in place and
maintained during transportation. The need for highly
skilled experts is reduced and local labour can do a
larger part of the installation. The commissioning costs
and OEM resources on-site will be reduced.
■Improved EMC
Electrical noise emitted is proportional to cable
length. The very short - or eliminated - cable
between motor control and motor in decentralized
installations therefore reduces emitted electrical noise.
In decentralized installations, the machine builder
normally mounts cables between motor controls and
motors in the machine leaving only power cables
and fieldbus cables with no EMC emission to be
installed at the production site. The risk of electrical
noise from motor controls to disturb other electrical
equipment caused by a faulty installation will diminish
and you avoid time-consuming fault finding in the
commissioning phase, where time frame is tight.
■Adapts to standard and special motors
Danfoss’ decentralized motor controls, FCD 300
and DMS 300, are designed to control standard AC
asynchronous motors. Their flexibility allows them
also to adapt to special motor types. An example
is the AMT feature (Automatic Motor Tuning) in the
FCD 300. Combining Danfoss adjustable frequency
drives to Danfoss geared motors makes it even easier
as they fit mechanically and the motor data are
already stored in the FCD 300 memory. Combined
motor-drives are provided pre-assembled directly
from Danfoss removing the need for mechanical
fitting between motor and control.
Danfoss geared motor with FCD 300
■Minimum thermal losses
Danfoss adjustable frequency drives feature the unique
VVC switch principle to generate motor voltages.
Due to the VVC principle, power losses in the
motoraresimilarorlessthanthelossesinamotor
connected to line. Thermal losses are minimized
and overheating is prevented. At the same time, the
VVC principle ensures nominal torque at nominal
speed and eliminates bearing currents.
Slim DC-links
It takes two steps to convert the frequency to vary
the speed of an AC motor: A rectifier and an inverter.
As the rectifier itself produces a rippled DC voltage, a
capacitor is often introduced to smooth the voltage
supplied to the inverter. A link between rectifier and
inverter with only a small capacitor to even out the
voltage is called a "slim DC link". With a slim DC
link, the inverter will not be able to provide quite
the same voltage amplitude as supplied by the
line supply, leading to lower efficiency. A special
pulse-width-modulation can be used to compensate
the ripple from a slim DC link. In this case the output
voltage for the motor still does not reach the rated
supply voltage value leading to an over-consumption
of motor current up to 10% and this will increase
the motor heating. Low efficiency and need of an
oversized motor is the result. As torque decreases with
the square of voltage the application will be exceedingly
MG.90.F3.22 - VLT is a registered Danfoss trademark
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