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

ML Converter Topologies 17
Each switching cell has two possible states: upper switch active or lower switch active, which
can be represented by the cell state s x. The resulting output voltage is given by equation (3).
U
out
=
N
∑
x=
1
s * ( U −U
with (3)
x
Cx
C( x−1)
)
Preferably, capacitor voltages are chosen such that each cell is generating the same output
voltage step. This dimensioning results in the availability of redundant states for all intermediate
output voltages, which is key for the control of the flying capacitors not having separate supplies.
This is the case if condition (4) is met.
U
DC
U
Cx
= x
(4)
N
Consequently, the number of available levels equals the number of cells plus one and the
output voltage levels can be generated as follows (N: total number of switching cells, n active_cells:
number of active cells at a given point in time)
U
U
DC
= ( nactive_
levels
(5)
N
out
)
The blocking voltage required in any flying capacitor switching cell is given by the adjacent
capacitor voltages; only the difference between input voltage and output voltage needs to be
blocked by any individual switch. Dimensioning according to (4) allows for all equal switching
devices with the same blocking voltage. The concept of the MC converter is very fundamental and
the same type of functionality can be found in many of the structures presented in the following
paragraphs, even if the corresponding MC circuits may be hidden.