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TMS320F28069: 28069 EPWM phase shift question

Part Number: TMS320F28069
Other Parts Discussed in Thread: TMS320F280049C

Hi,

We have some DC-DC code that is using TI support package in Simulink. We have 4 EPWMs configured. EPWM1 is acting as the master and the other 3 EPWMS are phase shifted from EPWM using WA and WB inputs to the simulink EPWM block.

The hardware guys have swapped EPWM1 and EPWM2. We have tried just swapping the blocks in the code but this doesn't work as EPWM1 (master has changed).

Question; Is there any way to change the master to EPWM2?

thanks

  • HI Graham,

    I have forward your question to MathWorks. Please expect a reply from them soon.

    Best Regards,

    Marlyn

  • Hi Graham,

    Documentation for ePWM is here.

    I dont know the exact answer, but will hazard a guess that you should investigate ePWMLink TBPRD - and assign it to EPWM2 if it is configured for EPWM1.

    For more assistance, please contact MathWorks Tech Support.

    Cheers,

    -Brian

  • Hi Brian,

    Thanks for the reply, I'll take a look at that. My question is regarding the processor peripheral detail so I think TI tech guys will have a better understanding than mathworks. All that mathworks do is place a dialog box and block for the TI peripheral.

    regards,

    Graham

  • Graham,

    The sync chain on this device connects ePWM1 to ePWM2, ePWM2 to ePWM3, and so on. There is a potential work around on other c2000 devices, you can use the external sync signal from ePWM2 and loop it back into the device syncing ePWM1. Unfortunately on F28069 you can only bring ePWM1SYNCO out of the device so that wont help you unless you plan on changing to something like an TMS320F280049C.

    So in short, no, ePWM2 cannot be ePWM1's Master.

    Have you already built hardware, if not the easy fix is just change the function of ePWM1 and ePWM2.

    If you have built hardware:

    1. What frequencies are your PWMs running at?
    2. What do you need to synchronize?
    3. Are you maintaining a phase relationship between anything, is that a constant or variable phases shift?

    Regards,
    Cody  

  • Hi Cody,

    Thanks for the reply, that's useful info.

    Yes, hardware is already built but I'm warming the hw guys up for a possible change.

    Our application is a dual active bridge DCDC converter (48v -> 400v). Simplified topology is an H bridge on either side of the transformer. High voltage side has EPWMs 1 and 2 and low voltage side has 3 and 4. Taking HV side, left leg uses EPWM1 a and b, right leg uses EPWM2 a and b.

    PWMs running at 60kHz.

    I need to check but I think all 4 EPWMs will be synced. Changing the phase shift on the EPWMs allows bi-directional current flow.

    regards,

    Graham

  • Graham,

    well I would say its always best to fix it before it becomes legacy. But since they are all at the same frequency you should be able to use ePWM1 as the master, syncing others to it. Even if you would like PWM2 to be the 'real master' you can always apply a negative or postive phase shift to ePWM1 relative to ePWM2. In this method you would keep ePWM2 at '0' phase shift and then phase shift 3 and 4 as your application requires relative to ePWM2 even though your sync pulse is actually coming from ePWM1.

    You would need to think through the corner cases with the workaround above, but for most systems I think it should work. Its just a little bit of additive or subtractive math, but you will need to decided if its better to rework your hardware.

    Best of luck, let me know what you decide to do and if I can provide any device specific help! 

    Regards,
    Cody 

  • Hi Cody,

    Thanks for clarifying. I agree, I think we will be able to coerce the software into working without making hw mods.

    I think all bases are covered so I'll close this ticket.

    Thanks again for speedy advice.

    Have a good holiday period.

    regards,

    Graham