Siemens SINAMICS PERFECT HARMONY GH180 Function Manual page 239

Calculation of desired Shaft Speed with Slip Compensation
If a speed other than synchronous speed is desired for shaft rotation, use the following equation
to calculate the desired speed demand.
With slip compensation, subtract the slip frequency from the output frequency (f
that the mechanical speed matches the desired speed. Multiply the per unit (pu) torque (T
the slip and subtract it from the speed feedback (in frequency), effectively adding it to the speed
reference:
3. S
4. S
In equation 4, S
for this is that for a speed command of 100%, based on the synchronous speed, the applied
electrical frequency will be higher than rated frequency due to the increase created by the slip
compensation. See equation 3 and 4. This will result in the motor running at true requested
mechanical speed with the electrical frequency adjusted to provide the torque necessary to
produce that speed.
Limiting Frequency by Disabling SlipCompensation
Slip compensation can be disabled to limit the motor to a specific electrical frequency. Using the
same example, set the Full load speed parameter (1030) to 1200 rpm. This disables the slip
compensation by reducing equation 2 to produce a slip of zero. Equation 3 and 4 reduce to:
1. Slip = (1200 – 1200) / 1200 = 0
2. S
The end result is that the drive will regulate to the output frequency rather than the motor shaft
speed (mechanical speed). No compensation for slip is done.
Summary
With slip compensation:
• Output shaft speed will equal the percentage of synchronous speed requested
• The frequency will vary depending on load but the speed will be fixed
• Monitor motor speed in rpm
Without slip compensation, set the Full load speed parameter (1030) to the synchronous speed:
• The output frequency will equal the speed demand percentage of rated frequency
• The mechanical speed, i.e. shaft speed, will vary with load but the frequency will be fixed
• Monitor motor frequency in Hz
NXGPro+ Control Manual
Operating Manual, A5E50491925A
= f – (Slip * T )
MOT OUT PU
= S – S
ERR DMD MOT
represents the error signal processed by the speed regulator. The implication
ERR
= f – 0 = f
MOT OUT OUT
Advanced Operating Functions
8.4 Slip Compensation
) to ensure
OUT
) by
PU
237