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TMS320F28027: Waveform output issue

Cherry Zhou
Mastermind 22235 points
Part Number: TMS320F28027
Other Parts Discussed in Thread: TIDM-HV-1PH-DCAC, SFRA

Hi team,

Here's an issue from the customer may need your help:

The output is 50HZ, switching frequency is 20K, and the chip is struggling with floating point operation at interrupts. The customer multiplies the period value with reference to the RAMP and sinusoidal calculation, and makes an array with such an inverting half-cycle with 200 array elements, the values in the array are calculated according to the code under the Voltage Source TIDM-HV-1PH-DCAC item.

Issue:

1) The battery voltage is 48 V, the modulation ratio is less than 1, and the inverting output waveform is 50 Hz, but the first half of each half is abnormal, please see below figure:

2) Is it possible to provide the open loop controlled waveform of the board output of this project? 

SFRA control is not used, and the open loop codes are as follows:

#if (INCR_BUILD == 1 ) // Open Loop Check
//-------------------------------------------------------------------------
#if (DC_CHECK==1)
invDutyPU = SFRA_F32_inject(invModIndex);
#else
invDutyPU = SFRA_F32_inject(invSine * invModIndex);
#endif
#endif // (INCR_BUILD == 1)

And they directly change to: invDutyPU  =invSine * invModIndex;

Could you help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Expert 4200 points

    Hi Cherry,

    Can you elaborate on what you mentioned? Do you have any blockdiagram or waveform that the customer want to implement? 

    "The customer multiplies the period value with reference to the RAMP and sinusoidal calculation, and makes an array with such an inverting half-cycle with 200 array elements, the values in the array are calculated according to the code under the Voltage Source TIDM-HV-1PH-DCAC item"

    Lab 1 is designed for the open loop operation. invDutyPU  =invSine * invModIndex is correct.

  • 0 in reply to John_K
    TI__Mastermind 22235 points

    Hi John,

    Thanks for your help. 

    John_K said:
    Can you elaborate on what you mentioned?

    20K 50HZ inverting waveform. The waveform is like oscillation every time the zero is passed. The inverting waveform is divided into positive and negative waves. The positive and negative junction is the zero position. At this time, the direction of the power output of the H-bridge is changed, and the PWM pulse width increases gradually to form the rising edge of the inverting waveform, but the rising edge is not smooth.

    What does this relate to? Or what caused it? The no-load waveform is shown above, and the band waveform is slightly smooth.

    John_K said:
     invDutyPU  =invSine * invModIndex is correct.

    The customer just followed this way, but above exception waves will occur. May we know where is the problem with the PWM output?

    Thanks and regards,

    Cherry

  • 0 in reply to Cherry Zhou
    TI__Expert 4200 points

    Hi Cherry,

    How was the control loop was designed? is it the same as the reference design?

    Also, what is the input and output voltage?

  • 0 in reply to John_K
    TI__Mastermind 22235 points

    Hi John,

    Sorry for the delay in feedback.

    John_K said:
    How was the control loop was designed? is it the same as the reference design?

    Basically the same.

    But they subtract each of the inverting outputs from the run-on capture to get the actual data without considering the AD deviation.

    Thanks and regards,

    Cherry

  • 0 in reply to Cherry Zhou
    TI__Mastermind 22235 points

    Hi,

    May I know is there any update? Thanks.

    Best Regards,

    Cherry

  • 0 in reply to Cherry Zhou
    TI__Expert 4200 points

    Hi Cherry,

    There is no way that I can duplicate this in my test setup. MCU model is different and the SW was ported to the different device.

    As mentioned in the other thread, supporting the the custom design is limited.

    Best,

    John