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TIDM-1000: Increase Switching Frequency

Nick Moore
Prodigy 10 points
Part Number: TIDM-1000

Tool/software:

Hi,

I'm working with the TIDM-1000 which is working fine at the default switching frequency of 50kHz.  I'm trying to increase the switching frequency, and my goal is to increase the PWM frequency without changing the frequency of the control loop or other control algorithms.  There are #defines for the PWM switching frequency and the current loop ISR ratio which sound like I can use them to increase the PWM switching frequency without increasing the control loop frequency.  However I quickly run into issues.  Above 100kHz the voltage loop performs poorly so I've been testing with just the current loop (Build 2).  It works well when I set the PWM frequency to 200kHz and the ISR ratio to 4, but when I try 250kHz PWM frequency and an ISR ratio of 5 it doesn't work.  I found that if I keep the ISR ratio at 4 I could increment the PWM frequency in 10kHz steps all the way to 260kHz.  Above that none of the voltages and currents are updated in the debugger and it seems stuck and unable to perform the control functions.  

I've tried several other combinations of PWM frequency and ISR ratio without success.  The other thing I tried was changing the SOC trigger event count for the ADCs that is generated by the PWM.  It was hardcoded to 1 and my understanding is this will trigger the ADCs to start converting every switching period.  I tried changing it to the ISR ratio so that it only performs a round of conversions once per control loop ISR but this didn't improve performance.

Any suggestions on how to increase the switching frequency higher (hopefully as high as 500kHz) would be greatly appreciated.

Thank You,

Nick

  • 0
    TI__Expert 5640 points

    Hi Nick,

    Firstly, TIDM1000 is validated at 50KHz. In your application if you are trying to increase the switching freq. to 250KHz. simulation validation need to be done whether the L and C on the design is feasible for such high frequency.

    Secondly, Once you are sure on the switching  freq. then comes the ISR freq.(or) control freq. you need to verify if the ISR ratio makes sense for all the lines of code. 

    For instance, if you keep ISR ratio to 4 with Fsw = 200kHz. then ISR freq. = 50KHz. here checks need to be done if the ISR code executes within 50KHz cycle this can be validated by profilling. then adjusting the control loop accordingly needs to be done. 

    Thanks & Regards,

    Uttam