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Original question:

UCC28950-Q1: PSFB transformer noise

UCC28950-Q1: DC link oscillations

keviv
Prodigy 80 points
Part Number: UCC28950-Q1
Other Parts Discussed in Thread: UCC28950

Tool/software:

Hi,

we are working on a 2 stage Multi level inverter in cascaded H bridge .it is observed that the DC link voltage starts to oscillate once the inverter starts switching.

C1 and C2 are DC link voltages (yellow and green respectively) C3 & C4 are EAP signal to controller.one common reference signal is fed to both compensator reference signal at non inverting terminal.

the error amplifeir is a typ2 compensator.

   

R2=100Ohms C1=.1uF,C3=1nF

R1=680 ohms R4=1k

below is the signal conditioning and compensator network from feedback divider to EAP control

Could you please share your thoughts

  • 0
    TI__Guru* 86266 points

    Hello,

     

    Your inquiry will be reviewed in the order it was received.

     

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86266 points

    Hello,

     

    It does look like the stages are not load sharing. This is a non-standard phase shifted full bridge, so, I do not have a lot of guidance that I can give for your specific design.  However, if you were doing two cascaded phase shift full bridge converters that could be possible. 

    To make sure these load share correctly I would use two UCC28950 controllers both reference to the same ground potential.   One controller to drive and control each PSFB.  You will need gate drivers, gate drive transformers or half bridge drives to drive all of the H Bridge Fets.

     

    To ensure they load share I would set one of the UCC28950 as a leader and the other as a follower.  Use the leader voltage amplifier to control the feedback loop.  You would set the followers amplifier up into a voltage follower and used the leader’s voltage amplifier output to the non-inverting follower

     

    You will need to sense the current of each PSFB with current sense transformer networks.  Each would have to be at the input of the full bridge converters.  You will also need to have a bulk capacitor across each PSFB.  The sensing networks would be from the bulk capacitor to the input of the respected H Bridges.

     

    Regards,