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

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42 ML Converter Topologies<br />

In a fully redundant MC converter, the voltage sequ<strong>en</strong>ce in the capacitors is giv<strong>en</strong>:<br />

yU<br />

U = DC<br />

y<br />

N<br />

(21)<br />

This can be inserted in the equation above<br />

2<br />

k / p<br />

k / p<br />

pN ⎛ yU ⎞<br />

DC<br />

p<br />

2<br />

K = ∑<br />

⎜<br />

⎟<br />

E cap<br />

= ∑ y<br />

(22)<br />

_<br />

Mk<br />

f _ sw y=<br />

1 ⎝ NU<br />

DC ⎠ MNk<br />

f _ sw y=<br />

1<br />

3<br />

( k / p) ( k / p)<br />

2<br />

p ⎛<br />

⎞<br />

⎜<br />

k / p<br />

K =<br />

⎟<br />

E _ cap<br />

+ +<br />

(23)<br />

MNk<br />

f _ sw ⎝ 3 2 6 ⎠<br />

E<br />

tot<br />

I<br />

U<br />

⎛<br />

3<br />

( k / p) ( k / p)<br />

2<br />

FC _ max DC p<br />

k / p FC _ max DC<br />

= KE<br />

_ cap<br />

= ⎜<br />

k fsw<br />

base<br />

MNk<br />

+ +<br />

(24)<br />

1 _<br />

f _ sw<br />

3 2 6 2k1<br />

fsw<br />

_ base<br />

2 ⎟ ⎝<br />

⎠<br />

⎞ I<br />

U<br />

Thanks to the parameterization, these equations can be used to calculate the total flying<br />

capacitor <strong>en</strong>ergy for a wi<strong>de</strong> range of differ<strong>en</strong>t topologies. The meaning of parameters shall be<br />

repeated here for clarity:<br />

TABLE 19, PARAMETER DEFINITIONS<br />

p<br />

k<br />

M<br />

N<br />

k f_sw<br />

number of id<strong>en</strong>tical groups of MC converters (non overlapping)<br />

total number of flying capacitors<br />

number of cells that can be operated interleaved<br />

input voltage divi<strong>de</strong>d by smallest capacitor voltage (number of cells in pure MC converter)<br />

switching frequ<strong>en</strong>cy factor to get actual maximum switching frequ<strong>en</strong>cy from maximum<br />

switching frequ<strong>en</strong>cy that can be used in the MC converter (f sw_base)<br />

k 1<br />

maximum allowable voltage ripple ratio ∆U/U N<br />

Dep<strong>en</strong>ding on the giv<strong>en</strong> boundary conditions differ<strong>en</strong>t parameters may be used. The following<br />

paragraphs list the resulting capacitor <strong>en</strong>ergies for three differ<strong>en</strong>t operating conditions: Operational<br />

limitation by peak switching frequ<strong>en</strong>cy of <strong>de</strong>vice, operational limitation by average switching<br />

frequ<strong>en</strong>cy of <strong>de</strong>vice and operational limitation by appar<strong>en</strong>t output switching frequ<strong>en</strong>cy of<br />

converter. The corresponding tables are giv<strong>en</strong> in app<strong>en</strong>dix 9.2.1.<br />

3.7.4.1.1 Operational limitation by peak <strong>de</strong>vice switching frequ<strong>en</strong>cy<br />

Operational limitation of a converter may be giv<strong>en</strong> by the peak <strong>de</strong>vice switching frequ<strong>en</strong>cy.<br />

This limitation may be based on two differ<strong>en</strong>t reasons. The first one being gate driving limitation,<br />

for example in the case where IGCT are used. IGCT gate drivers always have limited operating<br />

frequ<strong>en</strong>cy, optimized according to a tra<strong>de</strong> of betwe<strong>en</strong> cost and performance in its target application.

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