TMS320F28377S: EPWM1A and EPWM1B with independent modulation not working.

Hi Daniel,

Can you please explain how the rest of your code works? How you are changing the duty cycle of the outputs? How do you disable one and not the other? It would also be helpful to indicate what is channel A and what is channel B within the waveforms you attached. 

Best Regards,

Marlyn

Hi Daniel,

I see you have disabled dead band and pass through CMPA and CMPB, your code disables phase loading. Might it be CMPB is out of phase with CMPA by 180° when both are active?

Also if your intent is DC inverter zero switch H bridge or some other topology it would be wise to enable some kind of dead band control over MOSFET switching. Should x77 support direct control of CMPB dead band it might be good to configure ePWM A/B for complementary drive signals. Perhaps otherwise enable dead band to invert CMPB from CMPA.

Yes I am sorry I didn't mention that.

For both of these, the signal on top is the EPWM1A and the one on the bottom is the signal EPWM1B.

For the duty cycle code : Right now I am using a fixed value on the init for the CMPA and CMPB because it doesn't work like I want it. And if I want to test something out without reloading everything, I have a variable that changes CMPA and CMPB

But the duty cycle works fine if I only use EPWM1A alone and my code is like this to change the duty cycle : 

    control.uf.output_gen1_positive_only = func_gen.generator_1.out*2.0;        //func_gen.generator_1.out = sin 50Hz amplitude 1 pp, *2 for the signal to be at +1 and -1.
    control.uf.output_gen2_positive_only = (-func_gen.generator_1.out*2.0);     //func_gen.generator_1.out = Inverted sin 50Hz amplitude 1 pp, *2 for the signal to be at +1 and -1.
    if(control.uf.output_gen1_positive_only<0)
    {
        control.uf.output_gen1_positive_only = 0;
    }
    if(control.uf.output_gen2_positive_only<0)
    {
        control.uf.output_gen2_positive_only = 0;
    }
    
    
    epwm.modulator_1.in_modul = control.uf.output_gen1_positive_only*control.uf.input_duty;
    epwm.modulator_2.in_modul = control.uf.output_gen2_positive_only*control.uf.input_duty;

process_modulator(&epwm.modulator_1);

void process_modulator (struct modulator_t *const modulator)
{

	Uint16	temp;

	// 1 PU Limitation on input
	LIMIT(modulator->in_modul,0.0,1.0);

	// float -> pwm adaptation
	temp = (Uint16) (modulator->in_modul*PWR_IN_CNT_PRD); //PWR_IN_CNT_PRD max value of EPWM counter, 2500

	// Pulse Limiter min value
	if (temp <= modulator->pwm_min) temp = 0;

	// Pulse Limiter max value
	if (temp >= modulator->pwm_max) temp = (PWR_IN_CNT_PRD);

	// loading in compare register
	modulator->reg_handle->CMPA.bit.CMPA  = temp;

}

So like I said this part works fine if I only use A OR B.

Hope this helps and I am here if you have other questions.

Thank you

Daniel

Yes. I disabled the dead band because I don't want them to interact with each other, I want to set some value with CMPA and other with CMPB. They should be completely independent. (Maybe there is something I didn't understand and with dead band you can do that).

I tried to enable the phase loading with a value of 0 in TBPHS but I get the same result.

What I want to do is this :

Here it even says independent modulation. So It should be easy, but I am probably missing something :(

EPWMA is modulated by CMPA, EPWMB is modulated by CMPB. Without them blocking each other. That is all I want.

Thank you

Daniel

I found the issue, but thank you very much for your remarks and time. I put the solution under the post. Have a good day

Daniel

I found the issue, but thank you very much for your remarks and time. I put the solution under the post. Have a good day

Daniel

Hi Daniel,

No worries, it happens. Thank you for explaining the error and solution. I am glad you were able to resolve this within your application. Hope you have a great day as well. 

Best Regards,

Marlyn

Hi Daniel,

Sorry for late response we had bad storm 2 days no internet many trees went down. I was referring to some TI ePWM modules do not support independent dead band on both PWMA/B outputs without adding delay to A to make B, loosing Generator B in the process. Check the TRM for x377 MCU to see how the bits must be set to allow both A/B outputs independent dead band generators, not just pass through mode 1.

X49c MCU dead band is uniquely different has ePWM module type 4 if I recall correctly. 

Regards,