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Three phase rectifier

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devilwiss

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Hello

A three phase rectifier can fall to discontinous condution mode DCM under light loads and this makes the output voltage dependent on source voltage and phase shift of thyristors and also the load unlike the continous conduction mode where output voltage does not depend on load.

I want to know what are the pratical solutions to make the output voltage independent of load, given that the 3ph rectifier must work even with light load.

The solutions that i've tried are not practical (bleeder resistor or critical inductance since they lower the efficiency too much)

Thanks in advance.
schematic.jpg
This is the schematic of the three phase rectifier with the two stage LC filter.
 
Last edited:

Invalid Attachment specified.

but this works https://www.edaboard.com/attachment.php?attachmentid=89240

- - - Updated - - -

Load regulation is dependant on Impedance ratio of Source/Load.. When operating in DCM mode, source impedance gets high, so feedback compensation must change.

It is common for SMPS to require 10% pre-load or stable to 10:1 current range.

Here is DCM example with 300:1 range in output current.
 
You just need to improve your control - the controlled SCR approach can be used to set the Vout under all conditions...

Remember you want caps before the SCR's if you have inductors after - else the SCR's will be linking inductors at turn on - not a good idea!
 
The phase control of a 3 phase SCR bridge is similar to a 3 phase PWM except the switching frequency is much lower (60Hz vs 20KHz )
the LC filter is the same but the values are different. This is from my previous link.

recalculate using this design and use the ramp control to control the SCR phase. ESR and ESL of the cap and ESR of the inductor are important and included in the analysis. Typically ESR is given for caps for PWM (low ESR) but not always given for switched AC loaded caps so look at ripple current and estimate ESR from this, but get better parts and use this analysis.

The idea of the Caps after L is to reduce the output ripple.
Using caps before L reduces egress EMI issues.
 

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