Lenze i410 - Set Slip Compensation

9.2.5 Set slip compensaon
The speed of an asynchronous motor decreases as load is applied. This load-dependent speed
dr
op 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 for the funcon to generate the rated slip correctly 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
f
ollowing 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 the 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.
Conguring the motor control
V
/f characterisc control for asynchronous motor (VFC open loop)
Set slip compensaon
148