Drive control and features
41
Motor control features
Scalar motor control
It is possible to select scalar control as the motor control method instead of Direct
Torque Control (DTC). In scalar control mode, the drive is controlled with a frequency
reference. However, the performance of DTC is not achieved in scalar control.
It is recommended to activate the scalar motor control mode in the following
situations:
• In multimotor drives: 1) if the load is not equally shared between the motors, 2) if
the motors are of different sizes, or 3) if the motors are going to be changed after
motor identification (motor ID run)
• If the nominal current of the motor is less than 1/6 of the nominal output current of
the drive
• If the drive is used without a motor connected (for example, for test purposes)
• If the drive runs a medium-voltage motor through a step-up transformer.
In scalar control, some standard features are not available.
IR compensation for a scalar controlled drive
IR stands for voltage.
I (current) × R (resistance) = U (voltage).
IR compensation is active only when the motor
control mode is scalar. When IR compensation
is activated, the drive gives an extra voltage
boost to the motor at low speeds. IR
compensation is useful in applications that
require a high break-away torque.
In direct torque control (DTC) mode, IR
compensation is automatic and manual
adjustment is not needed.
f (Hz)
Motor voltage
No compensation
IR Compensation
50% of nominal
frequency
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