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

44 ML Converter Topologies
Limitation by average device switching frequency
Normalized total FC energy
3
2.5
2
1.5
1
0.5
0
2 4 6 8 10
MC
SMC
ANPC 1 SCx+FCx
ANPC 2 FCx+SCx
ANPC 3 FCx+FCx
FSx+FCx
FC2 * x
N = levels - 1
Figure 39, normalized FC energies in average device switching frequency limitation
In the case of a limitation by the average device switching frequency, SMC, ANPC1 and
ANPC2 require the same total flying capacitor energy, which corresponds with the ANPC1 energy.
At low number of levels, this number is even higher, e.g. more than 6 for N=4.
3.7.4.1.3 Operational limitation by apparent output switching frequency
Converter operation may also be given by a desired apparent output switching frequency.
There are two cases that can be considered:
1. constant apparent output switching frequency independent of the number of
levels
a. the losses decrease and the efficiency increases with rising numbers of
levels
2. the apparent output switching frequency scales with N
a. the losses stay constant assuming the same device characteristics (scaled
with voltage and current) even if the number of levels is changed
There are several cases where this type of limitation may be effective in reality:
1. Applications where the overall converter efficiency shall be maximized and
where apparent output switching frequency requirements are met and an
additional increase would not yield any benefit.
2. Applications where a very specific apparent output switching frequency is
required due to
a. The use of optimized pulse patterns at a given switching frequency
b. External filters requiring a certain spectrum
c. Limitation of the output spectrum due to EMC requirements