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Original question:

Phase current problem at motor high speed

TMS320F28027F: Phase current is not symmetric

even mi
Prodigy 105 points
Part Number: TMS320F28027F

Dear TI engineer,

I captured motor phase current waveform on shunts,It does't sinusoidal,it just looks like  lost the lower half.

what's the probable reason make it that?why the phase current waveform is different from waveform on shunt?

note:in figure below, blue waveform comes from current probe; purblish red comes from waveform on shunts

  • 0
    Prodigy 105 points
    I am sorry not introduce environment.Using user board(24v),shunts on the lower leg of inverter.run istaspin foc with over modulate.this phenomenon takes all the time from low speed to high speed. thanks
  • 0 in reply to even mi
    TI__Guru** 111990 points
    The phase current looks normal. The signal on the shunt resistor is very weak, you may check the signal on the output of amplifier. You will see the similar current sampling signal waveform as the phase current by current probe, but the current sampling signal is discontinuous with pwm signal.
  • 0 in reply to Yanming Luo
    Prodigy 105 points
    dear Yanming,
    I have been testing output of amplifier ,it show the same as waveform from shunts.So I put waveform on shunts in forum directly.
    I think signal on shunt is not weak because peak current flow it can up to 100 amper ( Rshunt = 1mohm ).
  • 0 in reply to even mi
    TI__Guru** 111990 points
    OK. What voltage is the offset of the current amplifier? What gain is the amplifier? What's the OVM index (USER_MAX_VS_MAG_PU)? Is it possible the output of amplifier overflow the range of its power supply?
  • 0 in reply to Yanming Luo
    TI__Guru** 111990 points
    HI Even,

    Just wanted to check in and see if there is any update from your side. I haven’t heard from you for a week, so I’m assuming you were able to resolve your issue. If this isn’t the case, please reject this resolution and reply to this thread. If this thread locks, please make a new thread describing the current status of your issue.