User Manual

Control concept
Superposed plant controls
5
CM110664en_07 87 | 351
● When the step-up demand signal [StepUp] persists for longer than the monitoring time deviation
[TiMonDev], and there are no further sequence steps to increase the power.
● When the step-up demand signal [StepUp] persists for longer than the monitoring time deviation
[TiMonDev] plus the step-up delay time of the next sequence step, AND a step-up would cause the
maximum power limit [MaxPwr] to be exceeded.
The process alarm is reset to normal:
● When a sequence step with an increase in power becomes possible again. Another sequence step with
an increase in power becomes possible when the [MaxPwr] limit will no longer be exceeded, or when a
further sequence step with a power increase is present.
● When there is no further [StepUp] demand signal
The text of process alarms can be defined to suit customer requirements.
Switching alternatives
Various switching alternatives can be defined by entries in the profile table. Note that where one or more
step-up sequence steps (intended to increase the power) would, in practice, result in a drop in the power
output, all steps in the step-up sequence are enabled automatically until a sequence entry is reached, at
which the power output actually does increase as required. See also the following example.
The power data in the object table and the sequence entries in the profile table in Figure
Example of
aggregate table
together give the power profile illustrated in Figure Example of profile entries with a drop in
power (Profile 2)
.
Profile 1
In the main application of the PWR_CTL function, a new energy producer is added for each sequence entry
in the profile table. For this purpose, an aggregate only needs to be entered in the sequence table once.
In the event of a power demand, which the boiler transmits to the PWR_CTL function in the form of the
[StepUp] demand signal, a further boiler stage / sequence step is enabled when the step-up delay has
expired. When a boiler reaches the stage limit, the function switches to the next boiler or boiler stage after
expiry of the switch-on delay. The last-enabled boiler stage is released to local power control, while all
other boilers are fixed at their current power output.
If the power needs to be reduced, this is transmitted to the PWR_CTL function via the [StepDn] demand
signal. The sequence steps are then executed in reverse order, with the defined switch-off and step-down
delay times.