Speed Control; Refsum_2 Function Block; Speed_Error Function Block; Speed Step For Testing - ABB DCS 500B Description

Functional Software description

• Speed Control

REFSUM_2 function
block
SPEED_ERROR func-
tion block
Speed Step for
testing

Error value filter

30
The function of the speed control is to adjust the torque reference
for the torque control so that the speed actual will be equal to the
speed reference.
The last function block of the speed reference chain is REF SUM.
The block adds [IN1] + [IN2] = OUT. The output OUT (11701) of
the ramp generator is connected to input [IN1] (1801) and possible
additional reference to [IN2] (1802).
The main task of the SPEED ERROR function block is to calculate
the difference between the speed reference in input [IN] (2001) and
speed actual SPEED ACT (12102).
Input [STEP] (2002) can be used, for example, during the commis-
sioning to make step response tests in order to find out the correct
PI-values for the speed control. [STEP RESP] (12003) output can
be used to monitor the speed response during the commissioning.
[STEP]
STEP RESP
Figure 15 Response for a speed step
The error between the speed reference and actual values can be
filtered by means of parameter FRS (2005).
Too much filtering should not be used, because it slows down the
control and easily causes transient overshoots in the response. It is
reasonable to find out the cause for disturbances, for example,
varying load, mechanics, settings of controllers, installation of a
pulse encoder, etc.
DCS 500 Software Description