Danfoss VLT DMS 300 Manual page 10

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.
10
Decentral Solutions
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 motor are similar or less than the losses in a
motor 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
sensitive to load-changes and speed sensors might be
required. At start, only nominal torque is available.
MG.90.F2.22 - VLT is a registered Danfoss trademark