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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3-L DC Link ML Converter Properties 79<br />
functions can be <strong>de</strong>scribed in closed form. The result of the rectification can be calculated for each<br />
harmonic individually:<br />
1. Each harmonic is inverted in the second half of the fundam<strong>en</strong>tal period (assuming zero<br />
phase shift of the fundam<strong>en</strong>tal)<br />
2. As a result only the fundam<strong>en</strong>tal is rectified. All others remain AC values, but with a<br />
changed spectrum.<br />
3. Harmonics can th<strong>en</strong> be combined and the complex spectra can be ad<strong>de</strong>d.<br />
4. If the harmonics are injected without phase shift (which is the normal case for 3 rd<br />
harmonic injection and 6 th harmonic injection), the resulting harmonics of the new<br />
functions also have zero phase. This means the absolute values of the differ<strong>en</strong>t spectra can<br />
be ad<strong>de</strong>d directly.<br />
In a g<strong>en</strong>eral approach, the function s x(t) shall be constrained in the following way:<br />
1. The function s x(t) shall contain either harmonics or a DC compon<strong>en</strong>t, but not both at the<br />
same time<br />
2. The function s x(t) shall have exactly two equidistant zero crossings per fundam<strong>en</strong>tal period.<br />
3. The position of the zero crossings shall be <strong>de</strong>termined by the fundam<strong>en</strong>tal term alone<br />
Consequ<strong>en</strong>tly, there are two distinct cases to be analyzed:<br />
i<br />
NPx<br />
( t)<br />
= i ( t)* (1 − abs(<br />
k + m sin( ωt)))<br />
(71)<br />
x<br />
x<br />
x<br />
Note that there is no g<strong>en</strong>eral function s x(t) specified in (71) but the function k x+m xsin(ωt). This<br />
means the equation is only applicable for a pure sine with a DC compon<strong>en</strong>t.<br />
i<br />
NPx<br />
( t)<br />
= i ( t)*(1<br />
− ( s ( t)*<br />
sign(sin(<br />
ωt))))<br />
(72)<br />
x<br />
x<br />
This is applicable for any function with a dominant fundam<strong>en</strong>tal according to the above<br />
constraints and no DC compon<strong>en</strong>t. Both spectra can be <strong>de</strong>termined in closed form. The imposed<br />
constraints are of course a restriction not applicable in all cases in reality. Nonetheless, it is possible<br />
to <strong>de</strong>rive quite universal control laws, as will be shown in the next chapter.