Rockwell Automation 20D PowerFlex 700S with Phase I Control Reference Manual - Manual (Page 63)

Rockwell Automation Publication PFLEX-RM002D-EN-E - August 2013 63
Detail Drive Configuration and Operation Chapter 1
Preset Frequency Search
The preset frequency search starts the frequency search at the value set in
parameter 451 [SrLss Preset Spd]. From this initial search frequency the search
will move towards zero. Once zero frequency is reached the algorithm will reset
to the opposite direction at the same initial frequency and again search toward
zero. If zero is reached a second time the drive will perform a start from zero
speed. The preset frequency search routine may take the longest to execute. The
value entered into parameter 451 [SrLss Preset Spd] should always be greater
than the expected speed of the motor. If the motor speed is greater than the initial
search frequency overvoltage trips could occur or the algorithm may not find the
correct motor speed.
If the flying start function is active and the drive is started with the motor at zero
speed the flying start search will add considerable extra delay to actually starting
the motor.
Figure 22 - Sensorless Flying Start From Last Known Speed
Figure 23 - Sensorless Flying Start From Preset Speed
Flying Start Frequency Search
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8
Time (seconds)
Fr
eque
nc
y
Motor Frequency
Pwm stopped
tracking rotor speed
tracking lost
frequency= 0
drive re-started
Frequency search
from last known
speed
Rotor Speed Found
Accel to set speed and
resume normal operation
motor at
50% speed