VSD Series Drives User Manual Powered by Eaton Technology
15-16 For more information visit: www.johnsoncontrols.com LIT-1201828
November 2009
602 V/Hz optimization
Automatic
torque
boost
The voltage to the motor changes automatically which makes the motor
produce sufficient torque to start and run at low frequencies. The voltage
increase depends on the motor type and rating. Automatic torque boost
can be used in applications where starting torque due to starting friction
is high, e.g. in conveyors.
Example 1:
What changes are required to start the load from 0 Hz?
● First set the motor nominal values (Parameter group 1.1).
Option 1: Activate the Automatic torque boost.
Option 2: Programmable V/Hz curve
To obtain the required torque, the zero point voltage and midpoint voltage/frequency
(in parameter group 1.6) need to be set, so that the motor can draw enough current at
the low frequencies. First set parameter ID603 to Programmable V/Hz curve (value 2).
Increase the zero point voltage (ID608) to get enough current at zero speed. Then set
the midpoint voltage (ID607) to 1.4142*ID608 and the midpoint frequency (ID606) to
ID606/100%*ID111.
Note: In high torque — low speed applications — it is likely that the motor will
overheat. If the motor has to run a prolonged time under these conditions,
special attention must be paid to cooling the motor. Use external cooling for the
motor if the temperature tends to rise too high.
603 V/Hz ratio selection
Linear:
0 The voltage of the motor changes linearly with the frequency in the
constant flux area from 0 Hz to the field weakening point where the
nominal voltage is supplied to the motor. A linear V/Hz ratio should be
used in constant torque applications. This default setting should be used
if there is no special need for another setting.
Squared:
1 The voltage of the motor changes following a squared curve form with
the frequency in the area from 0 Hz to the field weakening point where
the nominal voltage is supplied to the motor. The motor runs under
magnetized below the field weakening point and produces less torque
and electromechanical noise. A squared V/Hz ratio can be used in
applications where the torque demand of the load is proportional to the
square of the speed, e.g. in centrifugal fans and pumps.
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