Problems with sine-triangle PWM generation

BMJoshi

Hello,

I have implemented sine-triangle pulse width modulation using the ePWM module. I am facing a strange problem. The timer 0 interrupt is set up for 20 us time step. The triangular wave frequency is 5 kHz. When I supply a three phase induction motor with this voltage, in the current, I am observing a disturbance at every 200 ms interval. There is no problem with the current sensing since this issue does not come when I sense the current for the motor fed with an autotransformer. It comes only with PWM-inverter fed motor. This does not seem to be a noise issue either, because of the low frequency at which it is coming!

Has anyone experienced this issue? The PWM output seems to be going wrong every 0.2 sec, what might be the reaon? Any suggestions-comments are welcome!

Also, when I reduce the triangular wave frequency to 1 kHz, the aforementioned disturbance starts coming at every 1 sec instead of 200 ms. I tried changing the TBCLK also, but no luck!

Thanks..

over 16 years ago

0 Maxime Lachevre over 14 years ago

Prodigy 30 points

Hello,

DId you try to modify the timer 0 interrupt step to see if the problem still occurs ?

0 ChrisClearman over 14 years ago in reply to Maxime Lachevre

TI__Guru** 119680 points

Once every electrical cycle "blip"?

What are your PWM duty cycles modulating between? Are you allowing them to go to 100%? What is dead-time?

Depending on what the blip is this could potentially be a mechanical problem with the windings. Do you have a similar motor you can try to verify?

0 Dionisio Ramirez Prieto over 13 years ago in reply to ChrisClearman

Intellectual 780 points

I have the same problem. Every 200ms the pwm signal vanishes, periodically. In my case I am not using the Timer 0 and the carrier frequency is set to 10kHz.

Anyone know how solve this problem?

Thank you

Dionisio

0 Vivek Sankaranarayanan98982 over 13 years ago in reply to Dionisio Ramirez Prieto

Expert 2115 points

Try to avoid 0% and 100% duty cycles. Multiply the CMPA value with a constant gain of less than 1, to avoid hitting the peaks. See if that helps.

Vivek

0 Dionisio Ramirez Prieto over 13 years ago in reply to Vivek Sankaranarayanan98982

Intellectual 780 points

Hello Vivek

I am using a constant duty cycle now (50%) and the problem remains. Now I only have the minimum code to start the pwm with this duty cycle and a infinite loop but nothing has changed. It seems to be something related to the pwm setup, may be the dead time, etc..., I am not sure yet.

Dionisio

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Problems with sine-triangle PWM generation