38 Rockwell Automation Publication 6000-TD004D-EN-P - November 2017
Chapter 1 Functional Descriptions
Skip Frequency Settings
This function is used to avoid a trip caused by sudden changes in current due to
motor resonance and fan surge.
This function is enabled by parameter Skip Frequency Enable (P089). There are
two bands – one is between parameters Skip Frequency 1 Lower Limit (P090)
and Skip Frequency 1 Upper Limit (P091), the other is between Skip Frequency 2
Lower Limit (P092) and Skip Frequency 2 Upper Limit (P093). If the setting-
frequency is within these two bands, it can skip the resonance range. The
following diagram shows that the setting-frequency will be changed
automatically into the upper limit of the bands while the speed is increasing, or
changed into the lower limit of the band while the speed is decreasing. The
recommended width of these intervals is one Hz.
Figure 15 - Skip Frequency Function Diagram
Start and Stop Sequence
The Start sequence function is used to improve starting torque and suppress the
current oscillation at low frequency. The Stop sequence function is used to
reduce the current oscillation at low frequency during the stop process. These
functions mainly include the flux building process control, boost voltage control,
and slip control.
The following parameters are used for these functions:
• 0...t1 = Flux Time (P454)
• t1...t2 = Flux Delay (P271)
• t2...t3 = Minimum Start Frequency During Time (P447)
• F_start = Minimum Start Frequency (P448)
• Low Speed Voltage Compensation During Flux Building Process (P449)
Make sure there is no overlap between two bands when setting the
parameters.
Drive recognize Freq
User set Freq
fB2
fB1
fA2
fA1
P090 P091 P092 P093
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