Rockwell Automation 1336T FORCE Series B - Manual (Page 279)

Appendix A
A–31
velocity bandwidths than Mode 5 and allow smoother acceleration.
The disadvantage of this mode is that the response to load changes at
low speeds is not as fast as mode 5. Also, fast speed reversals may
not work when the preset speed is ramped from a PLC and the drives
accel/decel rate is set to 0.
Sensorless Troubleshooting Procedures –
– Problem: Motor won’t accelerate or doesn’t start smoothly
– Possible Solutions:
Increase the bandwidth. If the bandwidth is too low, there is a chance
the motor won’t accelerate, although the current will increase to
current limit.
If the regen power limit is 0, increase it to at least –5%.
Decrease the acceleration time. (faster acceleration)
Change Param 150 to mode 7.
– Problem: Motor oscillates after it is up to speed
– Possible Solutions:
Decrease the bandwidth if the process will allow. If this doesn’t help,
set Param 142 to 1500.
If unstable in field weakening, change Param 174 to 100%.
– Problem: Inverter trips on absolute overspeed during starting
Increase the bandwidth.
If the overspeed occurs during a reversal, increase the deceleration
time (slower deceleration).
Sensorless Fine–Tuning Procedures –
– Improving Speed Regulation
Typically the speed regulation (as a function of load) in sensorless
mode can be improved by adjusting Param 246 (Base Slip Frequency)
after the drive has been completely auto–tuned. This parameter is
originally calculated during the torque calculation section of
auto–tune and is dependent on the nameplate speed of the motor.
Ideally this adjustment is made while the motor is fully loaded and at
its normal operating temperature. Adjust Param 246 until the actual
speed, as measured by an independent source (i.e. hand tach), is equal
to the desired speed. This should result in a minimum steady state
speed deviation as load changes. The proper slip for good speed
regulation is also motor temperature dependent, thus if the motor
operating temperature normally varies between cold and hot, a
compromise slip must be selected.
– Minimizing Acceleration Time from 0 Speed
After a start command is issued, there is a 0.5 sec flux up delay before
the motor will start accelerating with sensorless control. This delay
can be eliminated in subsequent accelerations from 0 speed by
configuring the drive to decel down to a preset speed of 0 rather than
decelerating to stop.
– Increasing Speed Range
Speeds down to zero speed may be commanded when Param 150 is
set to 7. As operation nears 0, speed cogging may result.