ac/dc PFC + dc-dc

[zuirgham]

team, Planning to design a system consisting of PFC + LLC dc-dc stage.
Design specs are mentioned below.
Design Specs:

Input: 323Vac to 690Vac

Output 1: 14VDC/20A Constant Current Source for battery Charging

Output 2: 15VDC/15A Contant Voltage Source for Automotive Loads

Maximum Operating Temperature: 85 C

Cooling: Convection Cooling (No base plate and No Forced Air)

It's a three-phase delta connection, of which I'm making use of the two phases. since my wattage is low, i was considering of using a standalone controller. So, initially i had plan to proceed with UCC29950, but what the team at TI suggested is, "As the rectified voltage of this will be higher than a 1phase AC, 690Vac is too high for to be implemented with UCC29950, and they suggested to use Vienna rectifier or other 3 phase PFC topologies".

Link of TI suggestion:

UCC29950: ac/dc conversion + Battery charging + supply for other Automotive Loads - Power management forum - Power management - TI E2E support forums

Part Number: UCC29950 Team, I'm planning to use UCC29950 IC in to our design. Design Specs: Input: 323Vac to 690Vac Output 1: 14VDC/20A Constant Current

e2e.ti.com

The moment i go with the Vienna rectifier topology, my option would be limited to go with a digital controller, which would further increase the cost of the system. Is there a way to go without the digital controller or a more low-cost option? is there a topology i can look into for a better approach? what do you suggest out of your expertise?

 

[Easy peasy]

A couple of controlled flybacks ( 180 deg out of phase - if you are eductated enough ) , providing the raw LV DC with 100Hz ripple - followed by an efficient buck converter to regulate the output would be by far the easiest solution for 300W - gives unity PF and quite efficient at say 75kHz. 1200V Sic mosfet for low losses.

85 deg C & full power is a big ask if you have not done it before.

UC 3854N could easily control the flybacks

 

[mtwieg]

I'm not familiar with the UCC29950, but at a glance the highest voltage in its absolute maximum ratings is 20V. So it's not intended to directly see the line voltage. If it works at 120VAC then it should work at 1000VAC, if the external components are selected correctly.

The suggestion for a vienna rectifier seems bizarre. If the application permits you to use just two phases (and thus the resulting imbalance in the three phase system), then I see no advantage to a three phase rectifier.

A couple of controlled flybacks ( 180 deg out of phase - if you are eductated enough ) , providing the raw LV DC with 100Hz ripple - followed by an efficient buck converter to regulate the output would be by far the easiest solution for 300W - gives unity PF and quite efficient at say 75kHz. 1200V Sic mosfet for low losses.

If I understand the OP's specs correctly, their peak line voltage would be nearly 1000V. I don't see how flybacks with 1200V FETs could work, unless you're suggesting two-switch flybacks.

85 deg C & full power is a big ask if you have not done it before.

Yes this sounds like a big hurdle, especially with "No base plate and No Forced Air". Magnetics design is going to be critical.

 

[cupoftea]

Can you use all three phases, then a simple 6 diode rectifier...then from there, two LLCs...one for the 14v, one for the 15v.

 

[zuirgham]

A couple of controlled flybacks ( 180 deg out of phase - if you are eductated enough ) , providing the raw LV DC with 100Hz ripple - followed by an efficient buck converter to regulate the output would be by far the easiest solution for 300W - gives unity PF and quite efficient at say 75kHz. 1200V Sic mosfet for low losses.

85 deg C & full power is a big ask if you have not done it before.

UC 3854N could easily control the flybacks

Thanks for the response.
My quick updates:
1. @85 deg C, i'm not running the operation with full wattage. I should just be able to provide some AMPs to the battery, and maybe when the temp drops, i will go about full charging, that the approach.

2. As mtwieg suggests, my line voltage can reach peaks of about 1000V, can you please expand your knowledge on the flyback solution ?

--- Updated Apr 17, 2023 ---

I'm not familiar with the UCC29950, but at a glance the highest voltage in its absolute maximum ratings is 20V. So it's not intended to directly see the line voltage. If it works at 120VAC then it should work at 1000VAC, if the external components are selected correctly.

The suggestion for a vienna rectifier seems bizarre. If the application permits you to use just two phases (and thus the resulting imbalance in the three phase system), then I see no advantage to a three phase rectifier.

If I understand the OP's specs correctly, their peak line voltage would be nearly 1000V. I don't see how flybacks with 1200V FETs could work, unless you're suggesting two-switch flybacks.

Yes this sounds like a big hurdle, especially with "No base plate and No Forced Air". Magnetics design is going to be critical.

Thanks for the response. Could you explain more on the two switch flybacks ? So that i can look towards designing in that approach ?

 

[Easy peasy]

The 2 switch ( and 2 diode ) flyback ( or can be fwd too ) is a common solution to high voltage input aux supplies

when the fets turn off the flyback voltage is constrained by the additional 2 diodes to the input rail

for min Vin the rail must allow full output volts via the turns ratio

--- Updated Apr 17, 2023 ---

--- Updated Apr 17, 2023 ---

The 2 sw fwd:

 

[zuirgham]

The 2 switch ( and 2 diode ) flyback ( or can be fwd too ) is a common solution to high voltage input aux supplies

when the fets turn off the flyback voltage is constrained by the additional 2 diodes to the input rail

for min Vin the rail must allow full output volts via the turns ratio

--- Updated Apr 17, 2023 ---

--- Updated Apr 17, 2023 ---

The 2 sw fwd:

View attachment 182327

Thanks for your inputs.

As the voltage is high, Do you have some application notes or design notes where you can guide me to start off ?

 

[Easy peasy]

I do not store any app notes - we do our design from 1st principles