Siemens SINAMICS DCM Manual page 528

10.13 Speed controller
The speed controller is a PI controller with the following additional properties:
Start pulse
When starting the speed controller (i.e. when the controller is enabled) the I component can
start with a selectable value. This is necessary for suspended/hanging loads in order to
prevent the load from briefly sagging.
Adaptation
P gain and integral action time can be changed as a function of any signal (e.g. from the
actual speed value).
Droop
Droop (which can be switched in) can be implemented by feeding back the I component to
the input. As a consequence, the controller does not precisely control to the setpoint, but
permits a continuous setpoint-actual value deviation.
This is required, for example, if two drives are mechanically coupled with one another (e.g.
for a production machine where drives are coupled through the material web being
processed). In this case, the droop prevents that the two drives start to operate against one
another, although both operate with closed-loop speed control. In the case that a mechanical
connection is interrupted (e.g. if the material web breaks), then the speed of the drive
operating with droop only slightly changes.
Lead/lag element element
The lead/lag element is used to improve the stability of the speed control. If required, it can
be inserted in the actual speed value channel.
Remark:
The functions shown in function diagram 6810 have the following execution sequence:
● Generation of the speed setpoint (r52174)
● Selection of the actual speed value (r52167)
● PT1 element (r52179)
● Bandstop filter 1 (r52177)
● Bandstop filter 2 (r52178)
● DT1 element (r52169)
● Lead/lag element (r52156)
● Generation of the setpoint/actual-value difference (r52165)
Reference model
The reference model represents the P-controlled speed control loop and creates an
appropriately processed speed setpoint for the I-component. This means that the I-
component largely plays no role for setpoint changes, with the consequent improved,
overshoot-free response.
The reference model contains a PT2 element and a dead time element to emulate the
controlled system. See function charts 6810 and 6815.
Further, it is possible to feed in an external reference model (e.g. generated using DDC
function diagrams).
SINAMICS DCM DC Converter
Operating Instructions, 02.2015, A5E34763375/RS-AA/001
ac.maher.co.ir
Descriptions of functions
10.13 Speed controller
529