Bridgeless PFC Boost Converter: Floating Output

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PowerStarter_
Level 3
Level 3
10 questions asked First solution authored 10 likes given

Hello there,

in multiple papers, it is stated that the classical bridgeless pfc boost converter has bad EMI and the output is floating during negative half-wave.

"[...] in the Dual Boost PFC, the output ground is connected to the ac source only during positive half-line cycle through the body diode of switches. So large pulse current from high frequency switches will flow through parasitic capacitors and brings EMI problems." (Conduction Losses and Common Mode EMI Analysis on Bridgeless Power Factor Correction; Li, Qingnan and Andersen and Michael Andreas E. and Thomsen, Ole Cornelius)

Shouldn't the output ground be connected to the ac source during the negative half-line cycle through the Body-Diode as well?

Best regards

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1 Solution
Guruprasad_A
Moderator
Moderator
Moderator
25 likes received 250 sign-ins 50 solutions authored

Hi @PowerStarter_ 

Thank you for posting in Infineon community.

In conventional Boost PFC, AC input is rectified with a dedicated diode bridge and output power ground is always connected to AC neutral with a diode as shown in the figure below

Guruprasad_A_0-1664254775933.jpeg

In Dual Boost PFC,

During the positive half cycle, DC output GND is connected to AC neutral with the body diode of switch.

Guruprasad_A_1-1664254775950.jpeg

During the negative half cycle, DC output GND is connected to AC neutral with body diode of FET and inductor. And it is pulsating in nature.

Guruprasad_A_2-1664254775956.jpeg

In the reference (“Conduction Losses and Common Mode EMI Analysis on Bridgeless Power Factor Correction”; Li, Qingnan and Andersen and Michael Andreas E. and Thomsen, Ole Cornelius), page no 4, fig.8.a and 8.b show the nature of voltage waveform between power ground and neutral of ac source for conventional Boost PFC and dual boost PFC.

Please feel free to reach out to us if you need further clarification on this topic.

 

Regards,

Guruprasad A

View solution in original post

3 Replies
Guruprasad_A
Moderator
Moderator
Moderator
25 likes received 250 sign-ins 50 solutions authored

Hi @PowerStarter_ 

Thank you for posting in Infineon community.

In conventional Boost PFC, AC input is rectified with a dedicated diode bridge and output power ground is always connected to AC neutral with a diode as shown in the figure below

Guruprasad_A_0-1664254775933.jpeg

In Dual Boost PFC,

During the positive half cycle, DC output GND is connected to AC neutral with the body diode of switch.

Guruprasad_A_1-1664254775950.jpeg

During the negative half cycle, DC output GND is connected to AC neutral with body diode of FET and inductor. And it is pulsating in nature.

Guruprasad_A_2-1664254775956.jpeg

In the reference (“Conduction Losses and Common Mode EMI Analysis on Bridgeless Power Factor Correction”; Li, Qingnan and Andersen and Michael Andreas E. and Thomsen, Ole Cornelius), page no 4, fig.8.a and 8.b show the nature of voltage waveform between power ground and neutral of ac source for conventional Boost PFC and dual boost PFC.

Please feel free to reach out to us if you need further clarification on this topic.

 

Regards,

Guruprasad A

PowerStarter_
Level 3
Level 3
10 questions asked First solution authored 10 likes given

Hello there,

But when there are connections, why is then the output pulsating only during the negative half cycle? I don't quite get where it comes from. Maybe you can clarify it a little bit more. I would appreciate it.

Best Regards

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PowerStarter_
Level 3
Level 3
10 questions asked First solution authored 10 likes given

Hello there,
I think the issue occurs be cause during storing energy in the inductor there is not a direct connection  to the output.

In the following picture can be the negative charging-cycle can be seen. The red line indicates the current to charge the inductor. The grey line indicates the needed connection to keep the output fixed.

PowerStarter__1-1665148251959.png

 

During the positive charging-cycle (follwing picture), the output gnd is connected to the input gnd (grey line). The read line indicates the current to charge the inductor.

PowerStarter__2-1665148462129.png

 

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