4 Optimizing the PID controller
4.1 How to Control Process Works
How the Control Process Works
The
Testrun
explained in the chapter
PC Software interface
in the
APOSS Online help
can be used as a tool to optimize
the MCO 305 controller settings, thereby optimizing
system performance. To do that you only need to know a
few things about the control scheme of MCO 305:
The APOSS position controller has two parts:
1.
The
Setpoint Generator
interprets the various
positioning commands in APOSS and generates a
series of setpoint positions that eventually ends
with the desired position. Normally, all
positioning processes have a trapeze-shaped
velocity curve. That means that after a phase of
constant acceleration there is a phase with
constant velocity and finally a phase with
constant deceleration, which ends at the desired
target position.
2.
The
PID controller
receives the setpoint positions
from the
Setpoint Generator
and in turn calculates
the speed reference needed for the motor to
follow the current setpoint position. By setting
the PID control parameters you can directly
influence to what degree and how quickly a
deviation from a theoretical set path (as specified
by the setpoint series) should be counteracted.
The following behavior indicate that the control
parameters are not optimally adjusted:
-
Frequency converter vibrates
-
Frequency converter is loud
-
Frequent occurrence of position errors
-
Poor control accuracy
NOTE
The control parameters are load-dependent. Thus the
frequency converter must be optimized under the actual
conditions of use.
In exceptional cases it may be necessary to determine
various sets of control parameters while working with
heavily changing load conditions and to re-program them
in subsequent application programs depending on the
motion process.
4.2 Significance and Influence of the
Controller Parameters
The PID control unit of the MCO 305 motion controller
transfers the necessary output frequency via an internal
speed reference to the VLT AutomationDrive. This set value
is periodically recalculated with an interval of one
millisecond (interval is programmable by the TIMER
parameter). The MCO 305 is by default set with soft “fit for
all” controller parameters.
Optimizing the PID controll...
MCO 305 Operating Instructions
MG.33.K3.02 - VLT
®
is a registered Danfoss trademark
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