ABB ACS 600 Supplement To Firmware Manual page 26

Chapter 4 – Parameters
4-8
When the speed error moves outside the window, the exceeding part of
the error value is connected to the speed controller. The speed
controller produces a reference term relative to the input and gain of
the speed controller (Parameter 23.01 GAIN) which the torque selector
adds to torque reference. The result is used as the internal torque
reference for the ACS 600.
For example, in a load loss condition, the internal torque reference of
the drive is decreased, preventing the excessive rise of motor speed
(see Figure 4-2). If window control were inactivated, the motor speed
would rise until a speed limit of the ACS 600 were reached.
(Parameters 20.01 MINIMUM SPEED and 20.02 MAXIMUM SPEED
define the speed limits.)
ACS 600 Master/Follower Application Macro