Lenze i550

10.4.5 Set slip compensaon
The speed of an asynchronous motor depends on the load. This load-dependent speed drop is
called “slip”. The slip compensaon serves to counteract the load-dependent speed loss.
Precondions
The funcon is only eecve in the motor control type "V/f characterisc control (VFC open
loop)".
In order to determine the necessary nominal slip, the following parameters must be correctly
set:
•
Rated speed
•
Rated frequency
•
Number of pole pairs (automacally calculated from Rated speed and Rated frequency)
Details
The slip compensaon increases or decreases the output frequency as a response to a load
change. Thus, the slip is counteracted and the speed is kept constant.
Output frequency
Load
Motor speed
The rated slip required for the slip compensaon is calculated by the inverter according to the
following formula:
Rated slip [%] = (1 - (rated motor speed [rpm] / (120 * rated motor frequency [Hz] / number of
poles))) * 100
Calculaon example:
•
Rated motor speed = 1750 rpm
•
Rated motor frequency = 60 Hz
•
Number of poles = 2 * Number of pole pairs = 2 * 2 = 4
•
Rated slip = (1 - (1750 / (120 * 60 / 4))) * 100 = 2.77 %
The rated slip represents the reducon of the motor speed due to the motor load. At full
speed and full load, the motor given in the example would rotate with 1750 rpm, which
means 2.77 % below its synchronous speed of 1800 rpm. In order to compensate for this
speed loss, the inverter increases the output frequency by the rated slip mulplied by the
rated motor frequency. In the example, there is an increase in the output frequency at full
load of 2.77 % * 60 Hz = 1.66 Hz.
In order to take into account load changes, the inuence of the rated slip on output frequency
can be adapted in 0x2B09:001 (P315.01). A seng of 100 % corresponds to the rated slip of
the motor in the nominal operang point.
With reference to the example above and a setpoint frequency of 60 Hz:
•
If 0x2B09:001 (P315.01) = 100 %, the output frequency is = 61.66 Hz
(60 Hz + 100 % * 1.66 Hz).
•
If 0x2B09:001 (P315.01) = 50 %, the output frequency is = 60.83 Hz
(60 Hz + 50 % * 1.66 Hz).
Addionally, the lter me for the slip compensaon can be adapted in 0x2B09:002 (P315.02)
if required. The preset lter me is adapted to typical motors. If full load or nearly full load
oscillaons or instabilies occur, we recommend an increase of the lter me.
Extended sengs for idencaon ^ 217
Parameter
Address Name / seng range / [default seng] Info
0x2B09:001
(P315.01)
Slip compensaon: Gain
(Slip compens.: Slip: gain)
-200.00 ... [100.00] ... 200.00 %
Adjustment in percent of the slip calculated.
•
For instance required for deviaons of the real motor data from the
nameplate data.
•
A seng of 100 % corresponds to the rated slip of the machine in the
nominal operang point.
Conguring the motor control
V/f characterisc control for asynchronous motor (VFC open loop)
Set slip compensaon
183