meaning of SFRA_F_INJECT() ???

Thank you Manish,

I appreciate your help.

1.) My understanding is that the argument of the function SFRA_F_INJECT() is the dc point of the duty, i.e. a number from 0 to 1?? e.g. let's say 0.5 if I am analysing my frequency response based on a steady state duty cycle of 0.5. So inside the interrupt I can put the following,

//Add SFRA injection into the duty cycle for the open loop converter
Duty_pu=SFRA_F_INJECT(0.5);

Duty_pu is 0.5 + small signal perturbation as calculated by the function SFRA_F_INJECT in the interrupt.

2.) Can I ask you, in the function below, is "BUCK_PWM_PERIOD" the time base period of the PWM carrier? e.g. a number such as 500? if my PWM up carrier reaches the maximum value in 500 timer counts?

//Update PWM value
EPwm1Regs.CMPA.half.CMPA=((long)(BUCK_PWM_PERIOD))* Duty_pu;

Thank you again

Leo

Hi Manish,

Thanks for your help. I have finally managed to 'run' the SFRA, but I believe I am doing something incorrectly in the software. I have a buck converter, and I am trying to use the SFRA in open loop, around a steady state duty cycle of 0.5, my switching frequency is 200kHz, same as the interrupt frequency. In the software below the SFRA is always on (which is what I intended to do, but perhaps there are scaling errors, or other errors which I need help to find).

I report my main.c program below, with the parts I think are relevant for the correct config of the SFRA.

From the main.c:

...
#include "math.h"

...

#define MATH_TYPE 1 //FLOAT_MATH
#include "SFRA_F_Include.h"

...

define SFRA_ISR_FREQ 200000
#define SFRA_FREQ_START 1000
#define SFRA_FREQ_LENGTH 100
//SFRA step Multiply = 10^(1/No of steps per decade(40))
#define FREQ_STEP_MULTIPLY (float)1.0233//1.059253

SFRA_F SFRA1;
//extern to access tables in ROM
extern long FPUsinTable[];

float32 Plant_MagVect[SFRA_FREQ_LENGTH];
float32 Plant_PhaseVect[SFRA_FREQ_LENGTH];
float32 OL_MagVect[SFRA_FREQ_LENGTH];
float32 OL_PhaseVect[SFRA_FREQ_LENGTH];
float32 FreqVect[SFRA_FREQ_LENGTH];

int SFRA_flag=0;

float Duty_pu;

float Vpv_read;

...

// SFRA initialization

//SFRA Object Initialization
//Specify the injection amplitude
SFRA1.amplitude=0.1;
//Specify the length of SFRA
SFRA1.Vec_Length=SFRA_FREQ_LENGTH;
//Specify the SFRA ISR Frequency
SFRA1.ISR_Freq=SFRA_ISR_FREQ;
//Specify the Start Frequency of the SFRA analysis
SFRA1.Freq_Start=SFRA_FREQ_START;
//Specify the Frequency Step
SFRA1.Freq_Step=FREQ_STEP_MULTIPLY;
//Assign array location to Pointers in the SFRA object
SFRA1.FreqVect=FreqVect;
SFRA1.GH_MagVect=OL_MagVect;
SFRA1.GH_PhaseVect=OL_PhaseVect;
SFRA1.H_MagVect=Plant_MagVect;

SFRA_F_INIT(&SFRA1);

...

//***************************************************************************
// Infinite loop
//***************************************************************************
while (1) {

//*************** SFRA ***************
if(SFRA_flag == 1) {
SFRA_F_BACKGROUND(&SFRA1);
SFRA1.start =1;                                             // PS note I run the SFRA continuously
}
} // end of while(1)

....

interrupt void adcb1_isr(void) {

...

resultsbIndex = resultsbIndex + 1;

v_pv[resultsbIndex] = (double) (AdcbResultRegs.ADCRESULT4) * (-0.03953) + 74.91;

//Read ADC and computer Fbk Value

Vpv_read=(float32)v_pv[resultsbIndex]/4096.0;

//Add SFRA injection into the duty cycle for the open loop converter
Duty_pu=SFRA_F_INJECT(0.5);

//Update PWM value

EPwm6Regs.CMPA.bit.CMPA = ( ((PWM.PR)) * Duty_pu ); // Set compare A value to a certain TBPRD counts

EPwm6Regs.CMPB.bit.CMPB = (1.5 * PWM.PR); // condition never met -> PWM 6B always high (boost HO high, LO low)

SFRA_F_COLLECT(&Duty_pu,&Vpv_read);
...

AdcbRegs.ADCINTFLGCLR.bit.ADCINT1 = 1; //clear INT1 flag
PieCtrlRegs.PIEACK.all = PIEACK_GROUP1;
interrupt_exit++;

}

it is an adc interrupt triggered when the PWM CTR equals PRD. Below are other settings that may be relevant:

From ePWM6 settings:

...

//v2 ADC conversion related to switching EPWM6
EPwm6Regs.ETSEL.bit.SOCAEN = 1; // enable SOC on A group 
EPwm6Regs.ETSEL.bit.SOCASEL = 2; // EPWM6 SOCA Pulse Generated TBCTR=TBPRD //the ADC synch'd by the PWM
EPwm6Regs.ETPS.bit.SOCAPRD = 1; // Generate pulse on 1st event

...

From the ADC setup: (I am using ADC B-4, triggered by ePWM6)

...

AdcbRegs.ADCSOC4CTL.bit.CHSEL = 4; 
AdcbRegs.ADCSOC4CTL.bit.ACQPS = acqps; 
AdcbRegs.ADCSOC4CTL.bit.TRIGSEL = 15;

...

1) Now when the SFRA is run, all elements of the Plant_PhaseVect are 0.0 and never change, while the elements of the Plant_MagVect vector change and they are about -100 (a value that I did not expect).

2) Also, when I debug the main.c I get the following warning (I am not sure if I need to worry about) 

It also seems like that the switching frequency of the converter is changing: the pink waveform is the duty cycle of the converter, changing as the SFRA sweep moves to different frequencies, for different times. The yellow waveform is the voltage (the one I am trying to use in my SFRA)

Any help you could provide would be great.

Thank you so much again

Leo 

hi there, can anyone help on the question above? Thank you