Smart Logic Control; Extreme Running Conditions - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide

Smart Logic Control

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The Smart Logic Control (SLC) is essentially a sequence of user defined actions (see par. 13-52) executed by
the SLC when the associated user defined event (see par. 13-51) is evaluated as TRUE by the SLC.
Events and actions are each numbered and are linked together in pairs. This means that when event [0] is
fulfilled (attains the value TRUE), action [0] is executed. After this, the conditions of event [1] will be evaluated
and if evaluated TRUE, action [1]will be executed and so on. Events and actions are placed in array parameters.
Only one event will be evaluated at any time. If an event is evaluated as FALSE, nothing happens
(in the SLC) during the present scan interval and no other events will be evaluated. This means that
when the SLC starts, it evaluates event [0] (and only event [0]) each scan interval. Only when event
[0] is evaluated TRUE, the SLC executes action [0] and starts evaluating event [1].
It is possible to program from 0 to 20 events and
actions. When the last event / action has been
executed, the sequence starts over again from
event [0] / action [0]. The illustration shows an
example with three events / actions:
Starting and stopping the
Starting and stopping the SLC can be done by selecting "On [1]" or "Off [0]" in par. 13-00. The SLC always
starts in state 0 (where it evalutes event [0]). If the drive is stopped or coasted by any means (either via
digital input, field bus or other), the SLC automatically stops. If the drive is started by any means (either via
digital input, field bus or other), the SLC also starts (provided that "On [1]" is selected in par. 13-00).

Extreme Running Conditions

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Short Circuit
The frequency converter is protected against short circuits by means of current measurement
in each of the three motor phases. A short circuit between two output phases will cause an
overcurrent in the inverter. However, each transistor of the inverter will be turned off individually
when the short circuit current exceeds the permitted value.
To protect the drive against a short circuit at the load sharing and brake outputs please
see the design guidelines for these ports.
After 5-10 µs the gate driver turns off the inverter and the frequency converter displays a fault
code, depending on current, impedance and motor frequency.
Earth Fault
The inverter cuts out within a few µs in case of an earth fault on a motor phase,
depending on impedance and motor frequency.
Switching on the Output
Switching on the output between the motor and the frequency converter is fully permitted. You cannot
damage the frequency converter in any way by switching on the output. However, fault messages may appear.
Motor-generated Overvoltage
The voltage in the intermediate circuit is increased when the motor acts as a gen-
erator. This occurs in following cases:
Introduction to FC 300
SLC:
MG.33.B4.02 - VLT is a registered Danfoss trademark
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