Siemens SIMADYN D Manual page 472

Closed-loop thyristor current control
NOTE
Negative inverter
limit characteristic
5-32
When the closed-loop thyristor current control is switched-out (I=0), the
frequency at YFO corresponds to the offset error of the V/f converter in
the Sitor.
The output only indicates values up to 10% of the system current.
Connection CAV.XFO is an initialization connection and is only valid
after a restart \ reset.
CAV.XFO should be determined when commissioning the system and
after the SITOR-converter has been replaced.
Instructions are provided in the Section "Current sensing ".
The inverter stability limit is normally permanently specified at FB PC6
with a value. If the maximum output voltage is to be used, then the limit
must be adjusted as a function of the current, as the overlap angle
increases as a result of the extended commutation. This means that the
inverter stability limit must be reduced in order to avoid "Inverter
commutation faults". A current-dependent inverter stability limit YAU can
be calculated for these special applications.


= ° − ° −
YAU 180 90 arcsin

The variations of CAV.XF2 are shown in the diagram.
α
|YC| / ARC
w max
XF2(%)
20
2.0
1.8
1.6
1.4
1.2
1.0
0.8
XF2 limit
0.6
0.4
0.2
0
90° 120°
Fig. 5-15 Dynamic inverter stability limit
The data {≥0.7...1.3≤} at connection CAV.IAV results in an additional
correction of the dynamic stability limit.
The bandwidth of the correction of CAV.IAV decreases with CAV.XF2 ⇒
0.
Line supply changes can be taken into account here.

 
YC
XF 2

 
− ∗
1
 

IAV
ARC
f
= (XF2, YC)
10 5 4 3 2 1
150° 180°
System- and communication configuring D7-SYS - SIMADYN D
>
, with XF2 0
|YC| current actual value
(absolute value)
XF2 inductive voltage drop
of the converter
IAV correction for YUA
α
firing angle end pos.:
w
Inverter
α
w
Edition 06.2002