2.2.2 Control Structure Closed Loop (PI)
The internal controller allows the frequency converter to become an integral part of the controlled system. The frequency
converter receives a feedback signal from a sensor in the system. It then compares this feedback to a set-point reference
value and determines the difference, if any, between these 2 signals. It then adjusts the speed of the motor to correct this
difference.
For example, consider a pump application where the speed of a pump is to be controlled so that the static pressure in a
pipe is constant. The desired static pressure value is supplied to the frequency converter as the set-point reference. A static
pressure sensor measures the actual static pressure in the pipe and supplies this to the frequency converter as a feedback
signal. If the feedback signal is greater than the set-point reference, the frequency converter slows down to reduce the
pressure. In a similar way, if the pipe pressure is lower than the set-point reference, the frequency converter automatically
speed up to increase the pressure provided by the pump.
Reference
Feedback
S
+
-
*[-1]
PI
100%
0%
100%
-100%
Scale to
speed
To motor
control
P 4-10
Motor speed
direction
P 4-19
Max output
frequency (Hz)
7-30 PI
Normal/Inverse
control
195NA450.10
Illustration 2.9 Closed Loop Controller
While the default values for the frequency converter’s Closed Loop controller often provides satisfactory performance, the
control of the system can often be optimized by adjusting the Closed Loop controller parameters.
2.3 Local (Hand On) and Remote (Auto) Control
Operate the frequency converter manually via the local control panel (LCP) or remotely via analog/digital inputs or serial
bus.
Start and stop the frequency converter pressing the [Hand On] and [Off/Reset] keys on the LCP. Setup required:
0-40 [Hand on] Key on LCP
,
0-44 [Off/Reset] Key on LCP
, and
0-42 [Auto on] Key on LCP
.
Reset alarms via the [Off/Reset] key or via a digital input, when the terminal is programmed to "Reset".
Hand
On
Off
Reset
Auto
On
130BB893.10
Illustration 2.10 LCP Control Keys
Local Reference forces the configuration mode to open loop, independent of the setting of
1-00 Configuration Mode
.
Local Reference is restored at power-down.
Product Overview
VLT
®
DriveMotor FCP 106 and FCM 106 Design Guide
MG03M102 -
08/2015
13
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