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# Master of Science Thesis in Electric Power Engineering - page 19 / 114

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THREE PHASE CONTROLLED RECTIFIERS

# Finally, our minimum DC link voltage will be

2

(2.26)

√3

√2

2

2√2 √3

(2.27)

MINIMUM DC LINK VOLTAGE AND INDUCTANCE

The book [9] (chapter11 p434) defines a minimum DC link voltage taking in account the line inductance value. The demonstration seems to be valid in our case for amplitude invariant (they

assume a maximum converter voltage equal to

(i.e. radius of switching hexagon). It will be

for power invariant). They define a DC link voltage as

3

(2.28)

We can observe that R is neglected and if L = 0 (if there is no inductance voltage), we find again the

equation (2.25) where

√3

.

From this equation we can get the maximum inductance value as

3

(2.29)

A low inductance will give a high current ripple and will make the design more dependent on the line impedance (refer to “3.8 Grid modeling” and “3.9.3 Simulation results”). According to [9] , a high value of inductance will give a low current ripple, but simultaneously reduce the operation range of the rectifier. The voltage drop across the inductance controls the current. This voltage drop is controlled by the voltage of the rectifier but its maximal value is limited by the dc link voltage. Consequently, a high current (high power) through the inductance requires either a high dc link voltage or a low inductance (low impedance).

10

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