Christoph Haederli - Les thèses en ligne de l'INP - Institut National ...
Christoph Haederli - Les thèses en ligne de l'INP - Institut National ...
Christoph Haederli - Les thèses en ligne de l'INP - Institut National ...
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114 NP Control with Carrier based PWM<br />
5.3.2 SMC modulation<br />
The following applies to the <strong>de</strong>scription of the subsequ<strong>en</strong>t modulation schemes:<br />
- Dedicated carriers are used for each switching cell. This does not yield lowest harmonics in<br />
3 phase systems but is nice to illustrate the concept. Implem<strong>en</strong>tation can later be done<br />
with g<strong>en</strong>eric carriers to achieve PD PWM.<br />
- An in<strong>de</strong>x α L (0 to 1) is used for the output voltages from –U DC/2 to U DC/2, α 1 is the duty<br />
cycle of the upper cell, and α 2 is the duty cycle of the lower cell.<br />
- Ref is the refer<strong>en</strong>ce (phase leg) duty cycle α L = 0.625 applied as an exemplary operating<br />
point.<br />
- The commutation cells are numbered according to Figure 73<br />
C11<br />
C12<br />
C21<br />
C22<br />
Figure 73, 5-L SMC and cell numbering<br />
5.3.2.1 Standard SMC modulation<br />
With the basic modulation scheme shown in Figure 74, only the upper FC converter of the<br />
SMC is modulated for output voltages above zero (α L>0.5). It can be se<strong>en</strong> that the switching cells<br />
C21 and C22 are not used for the output voltage chos<strong>en</strong> in the giv<strong>en</strong> example. The resulting<br />
average phase NP curr<strong>en</strong>t is 75% of the phase output curr<strong>en</strong>t. The flying capacitor is operated with<br />
an AC curr<strong>en</strong>t with its fundam<strong>en</strong>tal at twice the carrier frequ<strong>en</strong>cy.<br />
Figure 74, SMC standard modulation (α = 0.625)