Siemens SINAMICS PERFECT HARMONY GH180 - Slip Compensation

8.4 Slip Compensation
NEMA B induction motors require slip of the rotor speed (rpm) relative to the stator speed
(frequency) to develop torque. The amount of slip is directly a󹪜ected by the loading of the
machine. For induction motors, the control provides slip compensation to the speed reference
to allow the motor to run at commanded speed, regardless of the torque output required.
Slip compensation operates as an open loop speed regulator that increases the electrical output
frequency of the drive as the load increases, or decreases the frequency of the drive as the load
decreases, to maintain commanded speed regardless of loadconditions.
E󹪜ect of Slip Compensation on Motor Speed with NXGPro+Control
With slip compensation, the electrical frequency is always greater than the desired shaft speed,
i.e. mechanical frequency, for all non-zero loads. Therefore at 100% speed demand, Open Loop
Vector Control (OLVC) will maintain the shaft speed at the rated synchronous speed of the
motor, not full load speed.
Example: Operation of the Slip Compensation for a 6-pole Motor
A 6-pole motor rated for 60 Hz has a synchronous speed of 1200 rpm.
Enter the full load speed from the nameplate, e.g. 1192 rpm, to Full load speed parameter
(1030).
Sending a speed demand of 100% will produce a mechanical speed, i.e. shaft speed, of
1200 rpm with slip compensation. This will result in a higher output (electrical) frequency, to the
motor, to provide the necessary torque to achieve the desired speed. The slip frequency is
directly proportional to the required torque, up to the rated torque current. Depending on the
selection, the display will show:
• Motor speed, in rpm, of 1200 rpm
• Motor speed, in percent, of 100%
• Motor frequency, in Hz, of 60.4 Hz at rated torque or if motor frequency is displayed in
percent, 101%
Calculation of Synchronous or Rated Speed
Sending the drive a speed demand of 100% means that you desire synchronous or rated speed.
To calculate, follow equation 1.
Synchronous speed, Ns, is de󹪝ned by the formula:
1. N
S
= 120 * f
RATED
/ # of poles
Calculation of Slip
At rated torque, slip is de󹪝ned as a percentage of the di󹪜erence between synchronous and full-
load speed (N
FL
) divided by the synchronous speed:
2. Slip (%) = 100 * (N
S
– N
FL
) / N
S
Advanced Operating Functions
8.4 Slip Compensation
NXGPro+ Control Manual
236 Operating Manual, A5E50491925A