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TMS320F280049C: Charging a battery using a digitally controlled boost converter

Mohan Nagella
Prodigy 130 points

Part Number: TMS320F280049C
Other Parts Discussed in Thread: BOOSTXL-BUCKCONV, SFRA

Tool/software:

Hello TI,

I am working on a project with digitally controlled boost converter customized from BOOSTXL-BUCKCONV example.

My my task is to charge a 24V battery with 2A during CC mode and later on switch to CV mode with 28V output setpoint. My input is 12V, 250W max.

I worked on compensator design and extracted PID parameters both during CC and CV mode of operation on Boost converter. These entire design process was carried out on a resistive load of 6.6Ohm

Now comes the main part. Initially I started with following test setup to test CC mode of operation of my digital controller

Output PSU @22V, 0.5A (to simulate battery being connected to my converter output ) connected to EL with CV mode setup @23V, 5A (to sink power delivered from converter output) ---> mock battery setup on output

Input PSU @12V, 250W 

Problem: When I start with current regulation of 0.2A, the output voltage spikes and my inductor current trip protection is triggered thereby switching off my entire converter.

What I am doing wrong? My CC regulation works on resistive load but on above mock battery setup?

Do I need to first do CV regulation and bring my converter output to slightly above 23V so that current flows to the output and then switch to CC mode for regulating current ?

  • 0
    TI__Mastermind 23881 points

    Hi Mohan,

    Can you provide some waveforms or simulation diagrams so I can better understand your design?

    Regards,

    Peter

  • 0 in reply to Peter Luong
    Prodigy 130 points

    Hello Peter,

    Once again thank you for your response. I was running the converter in discontinous mode of operation and now I see minimum DACref is 0.25 while charging the 24V battery.

    And instead of electronic load I connected a real battery and was looking at the waveforms where I found out a strange behaviours in inductor current and output current waveforms.

    Yellow: Inductor current high side sensing

    Blue: Output current delivered to battery. 

    Purple: PWM pulse

    As marked in red there is this strange behaviour in PWM pulses where they wont turn off at right time and iL keeps rising and comes back to normal.

    Is is something related to slope compensation or PID tuning that is reflected on iL ?

  • 0 in reply to Mohan Nagella
    Prodigy 130 points

    The frequency of this spike is around 1.7kHz.
    My Fsw is 200kHz and my cross over frequency is around 1kHz. I was able to tune using ZPK parameters and sfra open loop response is as follows:

    The output current request is 3A with spike being around 3.16A and as u can see from above figures uC is doing this by increasing PWM on duration at these instants. I dont understand why this behaviour is happening. Is it because of PSU ? or something else going wrong?

  • 0 in reply to Mohan Nagella
    TI__Intellectual 2190 points

    Hi Mohan,

    Battery is a different from a resistive load. The resistance of the battery is typically in mΩ. For the current loop, gain of the current loop depends on "Vin/Rload". You are tuning the loop at R=6.6ohm. Let's assume that battery has resistance of 66mohm, then the cross over frequency with battery would be 100 times higher. Can you try to tune the loop using below setup? At the load, you can connect a DC source and E-load together to emulate a battery. E-load needs to be CC mode in this setup.



    Regards,
    Shaury