LAUNCHXL-F28379D: Adding Soft-Start Feature to Closed loop control

Hello,

Is there any help about this issue?

gG,

A number of example solutions from the Digital Power SDK use software-injected slew to moderate the rate of change on the output voltage, which resembles stair stepping.

The TIDM-DC-DC-BUCK might be a good example to see.

-Tommy

Also you can review the soft-start implemented in TIDM-1007. See page 66 of the User-Guide

Shamim

Hello Tommy,

I investigated the code of Buck_VMC_F2837xS (BOOSTXL-BUCKCONV). The code is complicated for beginners. However, I catch the point that I need to increase the output set voltage step by step.

QUESTION 1. I think softstart issue is done at this section of code. If yes, could you please explain the code more? Is there any graphical or detailed explanation document for this code.

#if INCR_BUILD == 1

	if (Duty1A_Set > (float)0.45)							// Clamp Duty command to 0.45 (Q24)
		Duty1A_Set = 0.45;

	Duty1A_slew_temp = Duty1A_Set - Duty1ASetSlewed;

	if (Duty1A_slew_temp >= Duty1ASlewRate) 			// Positive Command
	{
		Duty1ASetSlewed = Duty1ASetSlewed + Duty1ASlewRate;
	}
	else
		{
		if ((-1)*(Duty1A_slew_temp) >= Duty1ASlewRate) 	// Negative Command
			{
			Duty1ASetSlewed = Duty1ASetSlewed - Duty1ASlewRate;
			}
		else	Duty1ASetSlewed = Duty1A_Set;
		}
#else
	// Vout1SlewRate should be set as a positive value

	Vout1_slew_temp = Vref1 - Vout1SetSlewed;

	if (Vout1_slew_temp >= Vout1SlewRate) 				// Positive Command
	{
		Vout1SetSlewed = Vout1SetSlewed + Vout1SlewRate;
	}
	else
		{
		if ((-1)*(Vout1_slew_temp) >= Vout1SlewRate)	// Negative Command
			{
			Vout1SetSlewed = Vout1SetSlewed - Vout1SlewRate;
			}
		else	Vout1SetSlewed = Vref1;
		}
#endif

QUESTION 2.For my code, I think that increasing max duty limit step by step for PI C1 controller at every ISR is easier for me. Is there any drawback of this approach?

I set a counter for soft start implementation. Soft-start counter increases at each ISR that is designated for control loop calculations. Counter is matched at a maximum duty value e.g. 0.1 to 1 for 50~70 pwm pulses. Then, using "if" structure or "swich-case" structure codes i load it to the "pi_cur.Umax = max_duty"

I couldn't tried the code at my design. After learning you explain question 1, i will think of it too.

//
    //=====================================
    // LOOP 1 - SOFT START LOOP
    //
    if(PWMenable == 1 & FAULT_LOW1 == 1 & FAULT_UP1 == 1)
    {
            EPwm5Regs.TBPRD = period;  // Turn-on switching by loading period

         //SOFT-START FEATURE
         if(softstart_counter == 0)
         {
             max_duty=0.1f;
             pi_cur.Umax = max_duty;
         }
    }

    //
    //=====================================
    // LOOP 2 - SOFT START LOOP
    //
    if(PWMenable == 1 & FAULT_LOW1 == 1 & FAULT_UP1 == 1)
    {
        EPwm5Regs.TBPRD = period;  // Turn-on switching by loading period

         //SOFT-START FEATURE
         if(softstart_counter == 8)
         {
             max_duty=0.2f;
             pi_cur.Umax = max_duty;
         }
    }

    //
    //=====================================
    // LOOP 3 - SOFT START LOOP
    //
    if(PWMenable == 1 & FAULT_LOW1 == 1 & FAULT_UP1 == 1)
    {
        EPwm5Regs.TBPRD = period;  // Turn-on switching by loading period

         //SOFT-START FEATURE
         if(softstart_counter == 16)
         {
             max_duty=0.3f;
             pi_cur.Umax = max_duty;
         }
    softstart_counter++;
    }

Hello,

The page 66 only shows the waveforms. Could you please help me on implementation about where to find and how to use it.

Hello,

Thank you for help. I'm making progress. However, I have some questions as below.

Question 1)  For the code that I inserted (boostxl-buckconv), we only implement "step by step increase duty" or only implement step by step "increase desired output voltage" and both of them isn't implemented at the same time. Is it correct?

Question 2)  For the code that I inserted (boostxl-buckconv), I couldn't find how and where to use this step increased duty cycle. Yes, I find a code section. However, I couldn't find where they are implemented in order to have soft start for closed loop.

Question 3) If I don't want to implement soft start at ISR loop in order not to reduce real time proccess effort, so, where should I implement it. Should I do it at main infinite loop and how? Because there should be time calculations for limiting soft start duration. Because I dont use state machine sequencing. I just have a pwm triggered ISR loop and make my new duty calculations at that interval.