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TIDA-010210: Switching Frequency

Namita Pawar
Intellectual 680 points
Part Number: TIDA-010210

Tool/software:

Hi,

I am referring the design guide for 11kW 3 phase ANPC. The switching frequency used is 100kHz for inverter. If we increase that to 300kHz will that work fine with the existing controller.

Are there any limitations of controller PWM to switch at high frequency.

Another thing is if we change the microcontroller from F280049 to F28377D, will that be ok.

We are at initial phase of analysis so please let us know your inputs regarding applicability of controller on 300kHz switching frequency.

Thanks,

Namita

  • 0
    TI__Expert 3270 points

    Hi Namita,

    I am seeing the following difference:

    ISR time is going to be changed. Now it is operating at 50 kHz with respect to 100 kHz.... If you operate as it is at 300 kHz you will have 150 kHz ISR. You need to rescale the ISR timing.

    Another difference I am seeing is with the discretization of the PWM... Basically, your resolution is changing and becoming less.

    Thanks

    Best Regards

    Riccardo

  • 0 in reply to Riccardo Ruffo
    Intellectual 680 points

    Hello Riccardo,

    Thanks for your reply.

    You mentioned that the resolution will be changed and reduced, so basically, we are using 16 bit PWM. With that how much resolution will be reduced in terms of bits.

    Is there any effect on close loop current feedback and the internal vector processing?

    I am just worried if we can process the information and send back the updated PWM duty cycle within 3.33uS or not. The switching period is 3.33uS (300kHz).

    Thanks,

    Namita

  • 0 in reply to Namita Pawar
    TI__Expert 3270 points

    Hi Namita, 

    resolution of the pwm is dependent on the clock frequency and switching frequency.

    For example 120 MHz clock  and 100 kHz correspond to 600 steps of resolution if the carrier is counting up and down.

    If you increase the switching frequency then it will become 300 steps. 

    MCU is not going to be able to support 300 kHz ISR... you cannot executed all the ISR in just 3.3us. you need to decrease the ISR frequency. 

    Thanks

    Best Regards

    RIccardo 

  • 0 in reply to Riccardo Ruffo
    Intellectual 680 points

    Hello Ricardo,

    The steps that you mentioned is this TBPRD value mentioned in below equation.

    TPWM = (TBPRD + 1) x TTBCLK

    What ISR frequency you recommend for 300kHz PWM switching. Is it 150kHz? 

    Can we implement our PWM control logic with reduced ISR frequency?

    Thanks,

    Namita