• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 83 subscribers
  • Views 268 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMS320F280039: PSFB DCDC converter soft start queation

sangmo kim
Prodigy 210 points
Part Number: TMS320F280039


Tool/software:

Hi, I am Sangmo kim.

I develop Phase shift full bridge DCDC converter(reference TIDM 02000).

I want to know why current reference is difference as voltage error.

I control PWM as 55kHz and voltage error calculate current reference every 300kHz.

I am curious why the current reference value calculated from the voltage error value intermittently becomes very large.

Case 1. Voltage error is 0, but current reference vlaue is calculated.

Case 2. Voltage error is same, but current reference value is different.

Thanks,

Best regards,

Sangmo, Kim.

  • 0
    TI__Expert 4060 points

    Kim,

    Current reference  (fed to DAC) is output of 2p2z compensator. Input to this compensator is error between output voltage and reference voltage, if this error remains the same then compensator will increase its output trying to reduce that voltage error zero. If error is still non-zero then it will increase it further in next cycle. That is the reason error is growing large. You have to make sure that your feedback signal chain of both loop is intact.

    Regards,

    Sumit

  • 0 in reply to Sumit Patil1
    Prodigy 210 points

    Hi, Sumit.

    Thank you for your reply.

    I have one more question.

    In case 2, there is voltage error. So current reference is growing large. I got it.

    In case 1, there is no voltage error, but there is current reference, I don't know this reason.

    Additional, voltage current loop operate in CLA, 300kHz. Can I measure voltage error and current reference every 300kHz by DAC?  

    Thanks.

    Best Regards,

    Sangmo Kim. 

  • 0 in reply to sangmo kim
    TI__Expert 4060 points

    Hi Sangmo,

    For no voltage error case, output voltage is equal to reference voltage and to maintain that voltage across the load, we need to provide finite load current (amount depend on load value). Compensator output will stop rising at that finite value of current reference so that inner current loop can regulate that current across the load so that output voltage is equal to reference voltage and error will remain zero. At that finite current reference value, system equilibrium is achieved.

    For outer voltage control loop frequency, you can go higher but generally at 5~10 times slower than inner current loop. This is because the reference value of the inner loop which is the output of the outer voltage loop controller can be considered relatively constant. In PSFB, the inner controlled variable is current in transformer primary and outer controlled variable is voltage on capacitors charged by inner current loop. The voltages on capacitors normally are the slower variables which justify the choice of the current as the inner faster variable. If you try to keep it equal then dynamics of outer current loop will degrage inner current loop's performance.

     

    Regards,

    Sumit