A&D October 2006 Inverter commutation failure in line ... - Siemens

V11
I d
V41
i C1
L K
L S
L 1
V31
+
C1
-
V39
V35
R a
u 13
C3
-
+
i 3
L a
V42
i C2
V40
C2
L K
L S
L 2
V33
V12
+
-
V37
SBG
-
+
U q
Figure 4
Relevant circuits when a current, which was originally flowing through V11 and
V12, is quenched. Due to the currents produced (i C1 for the one half-bridge and i C2
for the other), the full load current I d commutates first to the quenching capacitor
paths. The load current then recharges quenching capacitors C1 and C2 and
commutates to capacitor C3 or the voltage limiter SBG when the voltage is high
enough. The load current I d is then reduced to zero as a result of the difference
between the voltage at C3 and the source voltage U q .
9. Quenching process
The quenching process for the polarity of motor voltage and load current I d (motor current)
shown in Figure 3 is described below. The circuit must include quenching capacitors C1 and
C2 as shown in Figure 3. To illustrate this quenching process more clearly, Figure 4 shows
the circuits which are relevant for current flow in V11 and V12.
When the quenching thyristors V31, V39, V33 and V40 are fired by trigger unit ALE, the
currents commutate from both the upper half-bridge V11, V13, V15 to capacitor C1 and the
lower half-bridge V14, V16, V12 to capacitor C2. All currents in the converter operating in
regenerative feedback mode (V11, ..., V16) are quenched immediately. The motor voltage
polarity is reversed briefly by the quenching process.
At the same time as the quenching pulses (firing pulses for quenching thyristors) are output,
the firing pulses for the bridge SRB are disabled.
Version vom 5.10.2006 Seite 14 von 17 Wöhrer, Hofmüller, Himmelstoss