Christoph Haederli - Les thèses en ligne de l'INP - Institut National ...

ML Converter Topologies 27
(a) (b) (c) (d) (e)
Figure 31, Novel 5-L ANPC variations with different flying cap arrangement
The current paths and switching states for these topologies are not listed here for the sake of
brevity. However, they can be anticipated by comparing Figure 30 and Figure 31; Figure 33
illustrates a subset of converter states for Figure 31 (a).
Note that a switch in common path for upper MC operation and lower MC operation can
always be replaced by two parallel or quasi parallel paths. For example the circuit in Figure 31 (d)
can be transformed into the circuit in Figure 32, now featuring three distinct current paths (SMC
type) with a more balanced loading of the switches than the circuit in Figure 31 (d). More ways of
implementation are obviously possible (exchanging capacitor positioning in upper and lower DC
link, exchanging NPC stage with SMC stage, etc.).
Figure 32, Novel 5-L topology with direct path from NP to output
All these concepts can also be extended to higher level converters, leading to a very vast
number of different circuits. Most of them are not really attractive for industrial implementation, as
they may be asymmetrical, feature a lot of different commutation loops to be designed and may
have highly unbalanced losses. The topologies in Figure 31 (a) and (b) are notable exceptions as
they are symmetrical.