Load Effect Compensation - TDE MACNO MINIOPD EXP User Manual

As an example we calculate the settings of the parameters in the case of a motor with a rated voltage
of 380 Volts and a frequency of 50 Hz, which we want to work at full flux up to 50 Hz and a constant
voltage from 50 Hz to 75 Hz.
Having traced the desired voltage-frequency we see that to program it is sufficient to use only one
section point (see diagram).
From the maximum speed frequency desired (P65) and from the maximum working voltage (P64) we
can calculate the P177 and P178 values with reference to the maximum values, while P175 and
P176 will remain at 0.
CURVE FOR MOTOR WORKING ALSO IN FLUX WEAKENING AREA

2.4.3 LOAD EFFECT COMPENSATION

2.4.3.1 VOLTAGE STATOR DROP COMPENSATION (START UP
UNDER LOAD)
Using P36 parameter it is possible to increase the voltage value at low frequencies so as to
compensate for the drop due to the stator resistance and so as to be able to have current and the
refore torque even in the start up phase; this is necessary if the motors starts up under load. The
value which can be set refers to the drop voltage on the Stator Resistor (P66) and can be adjusted
from 0 up to a maximum of 400.0%. Particular care must be taken in setting the P172 value as it
determines the current values fed at low speed: a value too low for P30 results in limiting the torque
of the motor, while a value too high results in feeding high currents at low speed, whatever the load
condition is.
In the start up under load it is useful to introduce a waiting time on the common 'converter running so
that the motor can magnetize itself, so that it has from the outset the torque expected available. The
P29 parameter makes it possible to quantify this wait time in milliseconds, in which the system is in an
on-line state, but the frequency reference is forcibly held at 0. The most suitable value for P29 should
be chosen according to the rating of the motor and the load conditions, but in any case should be
from a minimum of 400ms for motors of 7.5 KW up to 1s for motors of 55KW.
2.4.3.2 SLIP COMPENSATION
By using parameter P170 it is possible to partly compensate for the motor's fall in speed when it takes
up the load; the adjustment is in fact that regulation of motor controls stator frequency and does not
control the real speed.
This compensation is obtained by increasing the motor's working frequency by a quantity which is
proportional to the percentage working torque multiplied by the percentage value set in P170 , in
relation to the motor's rated frequency.
The value to be set depends both on the motor's rating and poles, in any case it can in general terms
vary from 4% for a 7.5 KW motor to 1,8 - 2.0% for 45 KW motors. In default the compensation is
excluded P170 = 0.
User's manual
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