TMS320F28335: questions about BLDC current loop control

Chen Tian

Part Number: TMS320F28335

Hi all,

I am recently studying the control of the BLDC current loop and I have encountered some problems

1)There is a sampling resistor on each phase of my driver board,when I run the Motor in openloop,I get the phase current waveform like this,I was sampling in the case of H-off and L-on.As you can see, the current fluctuations are very serious.So if I use this current to do the current loop control, the effect is not good,(although the average value of the control current equals to set value),Can you give me a little reference to improve the current waveform?

THANKS

over 6 years ago

0 Ramesh Ramamoorthy over 6 years ago

TI__Mastermind 27240 points

Did you see the scope plot of the current waveform?
If the motor inductance is too small, you can try a higher switching frequency.

0 Chen Tian over 6 years ago in reply to Ramesh Ramamoorthy

Prodigy 70 points

Hi, thanks for the reply，my pwm frequency is 20k and I use a 50% duty cycle，I tried to drive other motors and see their current waveforms and then I found almost all of these waveforms, the current spikes appeared when commutate，the motor commutation with hall sensor，can you tell me whether the phase current waveform is correct or is there something wrong？thanks again

0 Ramesh Ramamoorthy over 6 years ago in reply to Chen Tian

TI__Mastermind 27240 points

The waveform appears to be that of voltage across shunt resistor. It does not look like a motor current.

0 Chen Tian over 6 years ago in reply to Ramesh Ramamoorthy

Prodigy 70 points

Hi,thanks for reply again,In your opinion, the waveform is not a motor current waveform . Can you tell me how to get the phase current correctly?I don‘t have a resistor to measure the DC bus current,but have two resistors in low side of phase A and phase B.The way of sampling by PWM generating SOC to trigger ADC when high side is off and low side is on.

THANKS

0 Ramesh Ramamoorthy over 6 years ago in reply to Chen Tian

TI__Mastermind 27240 points

The sampling strategy is correct, but the waveform is not. If you have a current probe, capture the phase current waveform to see if it matches. That way you can guarantee the sampling is alright and the issue may be with how the PWMs are generated. It difficult to give a clear answer based on this plot.

0 Chen Tian over 6 years ago in reply to Ramesh Ramamoorthy

Prodigy 70 points

ok I will have a try and thanks~

0 Chen Tian over 6 years ago in reply to Ramesh Ramamoorthy

Prodigy 70 points

Hi,I found the reason of causing the problem,there is some noise with my hall sensor signal,when I add a filter,the waveform is OK.

0 Ramesh Ramamoorthy over 6 years ago in reply to Chen Tian

TI__Mastermind 27240 points

Good to know the issue is resolved, closing this thread

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TMS320F28335: questions about BLDC current loop control