Siemens MICROMASTER 411 - Manual (Page 123)

Issue 03/01 10 Engineering Information
MICROMASTER 411 & COMBIMASTER 411 Operating Instructions
6SE6400-5CA00-0BP0 123
PI setpoint
The PI controller controls the inverter frequency by comparing the actual system
behavior (via the feedback signal) with the desired system behavior. The desired
behavior is defined using a setpoint. The user selects the source of the setpoint
with parameter P2253. MICROMASTER 411/COMBIMASTER 411 only have one
analogue input and this is most commonly used for the feedback signal, so an
internal digital setpoint is usually used. There are two methods of doing this, either
using the “fixed PI setpoint ” or the “keypad (motorized potentiometer) setpoint”.
1. P2253 = 2224
Fixed PI setpoint
This method allows the user to define up to 7 setpoint
values using parameters P2201 to P2207 and select
between these using binary signals, usually via the digital
inputs. The different selection methods are described in
the parameter list under P2201.
2. P2253 = 2250
Keypad
(motorized
potentiometer)
setpoint.
This method allows the user to set a fixed value in
P2240. The setpoint can be increased or decreased
either with the arrow keys on the BOP or more commonly
via digital inputs (e.g. P0702 = 13 “increase” and P0703
= 14 ”decrease”).
NOTE:
Values are given in % rather than Hz, and the running frequency of the inverter is
determined by the difference between the setpoint and feedback signals and the
action of the PI controller.
10.2.2.4 PI Setpoint ramp times
When PI control is enabled using P2200, the normal frequency ramp up and ramp
down times (P1120 and P1121) are bypassed. The PI setpoint has its own ramp
times, P2257 and P2258, which allow ramped PI setpoint changes.
The ramp up time, P2257, is active when the PI setpoint is changed or when a
RUN command is given. The ramp down time, P2258 is only effective on PI
setpoint changes. The ramp down times used after OFF1 and OFF3 commands
are set in P1121 and P1135 respectively.