EMI issues in a bridgeless boost PFC converter

[biswaIITH]

Can some one explain why bridgeless boost PFC introduces significantly high conducted EMI noise??

 

[treez]

Bridgeless boost pfc is not at all common…..because if it is bridgeless, then (usually) the output of the boost pfc has to eventually be rectified…..which would mean using a bridge……but “bridgeless” is wanted so no bridge is used, and in fact, the rectification is achieved by using the rectifier of the downstream PWM stage……and in fact, to make things easier…….you use the downstream pwm stage as actually a single stage pfc……..eg the single stage PFC’d isolated cuk converter as used by Tesla motors…….or, as “said to be used” by Tesla motors.

Anyway, the problem with that is that you end up with severe noise issues when doing the switching, if you look at the bridgelss pfc’d isolated cuk converter you see what I mean……it needs a very special regenerative snubber

 

[biswaIITH]

Bridgeless boost pfc is not at all common…..because if it is bridgeless, then (usually) the output of the boost pfc has to eventually be rectified…..which would mean using a bridge……but “bridgeless” is wanted so no bridge is used, and in fact, the rectification is achieved by using the rectifier of the downstream PWM stage……and in fact, to make things easier…….you use the downstream pwm stage as actually a single stage pfc……..eg the single stage PFC’d isolated cuk converter as used by Tesla motors…….or, as “said to be used” by Tesla motors.

Anyway, the problem with that is that you end up with severe noise issues when doing the switching, if you look at the bridgelss pfc’d isolated cuk converter you see what I mean……it needs a very special regenerative snubber

Well,i read somewhere that in a bridgeless boost PFC, the input line source is in a floating condition w.r.t the PFC ground which charges and discharges any parasitic capacitance present between the two grounds which introduces large common mode noise.I also read that to as the input ac line is floating it is difficult to sense the input line voltage without using a low frequency t/f or an optocoupler.

I have got two queries

1)Can the EMI noise be reduced if try interleaving in the bridgeless configuration i.e. a bridgeless interleaved boost converter??

2)Can the line voltage be sensed directly in a bridgeless interleaved boost converter with out an opto coupler or a t/f

 

[Easy peasy]

1)Can the EMI noise be reduced if try interleaving in the bridgeless configuration i.e. a bridgeless interleaved boost converter??
2)Can the line voltage be sensed directly in a bridgeless interleaved boost converter with out an opto coupler or a t/f

You are correct about the extra CM noise produced, we did a state of the art design for samsung in 2004, a laptop adapter, 95-265Vac, 12.5V 18A at 91% efficient, this used a 2 FET, 2 diode "bridgeless" PFC stage, we had to invent a way to "see" the rectified mains waveform, and a low loss, and miniature CT solution to see the currents in the fets, we had to overcome the inherent CM noise on the rectified mains 0v, w.r.t. both the clean input mains and the other side of the main transformer, also we implemented one of the earliest synchronous rectified output stages (at 200kHz - 350kHz) to get the required efficiency inside a plastic box.

The answer to your Qu are 1) No, not that simple, a return diode is needed to reduce CM noise on the 0v
2) Yes, but you need to put some thought into it...

 

[biswaIITH]

Bridgeless boost pfc is not at all common…..because if it is bridgeless, then (usually) the output of the boost pfc has to eventually be rectified…..which would mean using a bridge……but “bridgeless” is wanted so no bridge is used, and in fact, the rectification is achieved by using the rectifier of the downstream PWM stage……and in fact, to make things easier…….you use the downstream pwm stage as actually a single stage pfc……..eg the single stage PFC’d isolated cuk converter as used by Tesla motors…….or, as “said to be used” by Tesla motors.

Anyway, the problem with that is that you end up with severe noise issues when doing the switching, if you look at the bridgelss pfc’d isolated cuk converter you see what I mean……it needs a very special regenerative snubber

How did you know that tesla motors is using the isolated cuk converter??

 

[treez]

because it says such on their website, Slobodan Cuk actually works for Tesla. He invented the Cuk converter.