Standard programposi features 59
Critical speeds (frequencies)
A critical speed function is available for applications where it is necessary to avoid
certain problems in motor speeds or speed ranges, for example, mechanical
resonance problems.
A similar function is available for scalar motor control with a frequency reference.
Example
A fan has vibrations in the range of 540 to 690 rpm and 1380 to 1560 rpm. To make
the drive jump over these speed ranges,
• enable the critical speeds function by turning on bit 0 of parameter 22.51 Critical
speed function, and
• set the critical speed ranges as shown in the figure below.
Settings
See parameter groups
• Critical speeds: parameters 22.51…22.57
• Critical frequencies: parameters 28.51…28.57
Speed controller autotune
The speed controller of the drive can be automatically adjusted using the autotune
function. Autotuning is based on an estimation of the mechanical time constant
(inertia) of the motor and machine.
The autotune routine will run the motor through a series of acceleration/deceleration
cycles, the number of which can be adjusted by parameter 25.40 Autotune repeat
times. Higher values will produce more accurate results, especially if the difference
between initial and maximum speeds is small.
The maximum torque reference used during autotuning will be the initial torque (ie.
torque when the routine is activated) plus 25.38 Autotune torque step, unless limited
by the maximum torque limit (parameter group 30 Limits) or the nominal motor torque
540
690
1380
1560
1Par. 22.52 = 540 rpm
2Par. 22.53 = 690 rpm
3Par. 22.54 = 1380 rpm
4Par. 22.55 = 1560 rpm
1234
Motor speed
(rpm)
Speed reference
(rpm)
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