Particular Control Functions - TDE MACNO MINIOPD EXP User Manual

2.4.4 PARTICULAR CONTROL FUNCTIONS

2.4.4.1 MOTOR FLYING RESTART
Since the driver has a maximum current limit it can always be started running with no problems even
if the motor is already moving, for example, by inertia or dragged by part of the load. In that event, on
starting up, given that normally the frequency reference starts from values close to zero to gradually
rise with the ramp times to the working value, the motor is first subjected to a sudden deceleration,
within the limit, to then hook onto the reference and follow it with the ramp; this may be undesirable
from a mechanical standpoint, and the process could also trigger the overvoltage alarm for
converters which do not have a braking device. To avoid this it is possible to suitably program
connection C84 , "Enable motor flying restart", which makes it possible to identify the speed of
rotation of the motor, stressing it as little as possible, and to position the output reference from the
ramp at a value corresponding to that rotation so as to start from that reference to then go on to
working values. This motor search function is primarily in one direction and thus needs to know in
advance the direction of rotation of the motor, positive frequency or negative frequency, which must
be programmed in C84 ; if the selection is wrong the motor is first braked to about zero speed to then
follow the reference to go to working speed (as if the search function had not been used). If there is a
passive load and the inertia keeps the motor in rotation, it's possible to select a search dependently
upon the sign of enabled frequency reference (C84=3-4).
There are two different values for C84 to enable this kind of search, the only difference is for manage
the case in which the frequency reference was zero: in this particular situation with C84=3 the system
searches for positive frequency, while with C84=4 the search will be made for negative frequency.
The C50 connection has five programming values which are selected as indicated below :
o C84=0 flying restart doesn't enabled
o C84=1 flying restart managed with positive frequency quadrant search
o C84=2 flying restart managed with negative frequency quadrant search
o C84=3 flying restart managed dependently upon the sign of enabled frequency
reference (like C84=1 for 0)
o C84=4 flying restart managed dependently upon the sign of enabled frequency
reference (like C84=2 for 0)
The start frequency in motor flying restart can be set in parameter P184 (default 100%) in percentage
of maximum frequency. This parameter can help the search algorithm limiting the range of frequency.
With parameter P185 it's possible to set the minimum target frequency in order to inject an active
current also if the motor is stopped.
If the maximum frequency is greater than 250% of nominal motor frequency could be some problems
in the motor flying restart because it's difficult to inject the active current with a slip so high. In that
case the only possibility is to reduce the start search frequency (with P184) on condition that really
the motor cannot run more quickly.
If it's enabled the motor flying restart, the power is switch-on with the motor standstill and
there is low load, it's possible to have a transient initial state in which the motor starts
If the flying restart doesn't work correctly it's possible to increase the reserved parameter P191
(default value 5%) for increase the admitted search window .
In default the flying restart isn't managed ( C84=0 )
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running in the searching sense
.