Siemens MICROMASTER 420 Reference Manual page 21

To access only the PI controller parameters, you can use the parameter filter as
follows:
P0003 = 2
P0004 = 22
PI control is enabled using parameter P2200. For constant enabling of the PI
controller this should be set to 1. It is also possible to use a digital input (or other
BiCo functions) to enable the PI controller, e.g. the PI controller can be enabled
using DIN 2 by setting P0702 = 99 and P2200 = 722.1. This allows the user to
switch between frequency control and PI control when the inverter is not running.
PI control requires a feedback signal from the process to monitor how the system
is behaving. For the majority of applications, this will be in the form of an analogue
sensor.
The MICROMASTER 420 has one analogue input, terminal connections 3 & 4, and
the feedback signal can be connected to this input. The source of the PI feedback
signal must then be defined using P2264 = 755 (source of PI feedback = analogue
input 1). If required the analogue input can be scaled using parameters P0757 –
P0760. If a different source of feedback signal is used (e.g. USS), P2264 must be
set appropriately. The value of the feedback signal can be viewed via parameter
r2266.
The relation between the sensor signal and the manner in which the PI controller
changes the motor frequency must also be defined at this point. This is done using
P2271 (PI transducer type). There are 2 possible settings for this parameter, 0 and
1. The difference between these settings is whether the PI controller increases or
decreases output frequency as a response to a positive error signal (i.e. where the
feedback signal is less than the setpoint). The parameter description for P2271
describes in detail how to determine which setting is correct for your application.
The PI controller controls the inverter frequency by comparing the actual system
behaviour (via the feedback signal) with the desired system behaviour. The
desired behaviour is defined using a setpoint. The user selects the source of the
setpoint with parameter P2253. The MICROMASTER 420 only has 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
2. P2253 = 2250
Keypad
(motorised
potentiometer)
setpoint.
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.
MICROMASTER 420 Reference Manual
Issue A1
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.
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").
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