Setpoint channel and closed-loop control
7.2 Setpoint channel
Inverter chassis units
322 Operating Instructions, 07/2016, A5E00331449A
Skip frequency bands and minimum speed
Description
In the case of variable-speed drives, it is possible for the control range of the overall drive
train to contain bending-critical speeds that the drive must not be be operated at or the
vicinity of in steady-state condition. In other words, although the drive can pass through this
range, it must not remain within it because resonant oscillations may be excited. The skip
frequency bands allow this range to be blocked for steady-state operation. Because the
points at which critical whirling speeds occur in a drive train can vary depending on age or
thermal factors, a broader control range must be blocked. To prevent constant speed step
changes in the vicinity of these skip frequency bands (speeds), they are provided with a
hysteresis.
The skip speed values apply in the positive and negative directions of rotation.
Specifying a minimum speed allows a specific range to be disabled around speed 0 rpm for
steady-state operation.
Figure 7-1 Signal flow diagram: Skip frequency bands and minimum speed
Skip frequency bands and speed limiting
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