LAUNCHXL-F28379D: Using ZPK format compansator for digital control

You can use the function "DCL_loadParallelPIasZPK" to load the zero frequency into the series PI_C1 controller. In the PI case you have only a gain, one configurable zero, and a fixed pole at the origin, so in the ZPK3 structure only K and z1 are relevant.

The "DCL_loadParallelPIasZPK" function takes a ZPK3 description, computes the series PI gains, and loads them into the shadow parameter set (SPS) of the controller. To use it, you'll need to declare and initialize instances of the SPS and CSS structures in your code. You'll then call the "DCL_loadParallelPIasZPK" function with your controller configuration, and finally update the controller by calling "DCL_updatePI()" in your background loop. You will also have to set up the sample rate in the CSS so the DCL knows how to interpret the z1 frequency.

Your ISR code does not need to change. You just need to add some declarations and code to your main file. Here is an example:

// sample rate definitions
#define SAMPLE_RATE 1000.0f
#define SAMPLE_PERIOD 1.0f/SAMPLE_RATE

// controller declarations
DCL_PI pi = PI_DEFAULTS;;
DCL_PI_SPS pi_sps = PI_SPS_DEFAULTS;
DCL_CSS pi_css = DCL_CSS_DEFAULTS;
DCL_ZPK3 zpk = ZPK3_DEFAULTS;

void main(void)
{

// initialize controller structs
pi.sps = &pi_sps;
pi.css = &pi_css;
DCL_SET_CONTROLLER_PERIOD(&pi, SAMPLE_PERIOD);

// load controller parameters
zpk.K = 12.3f; // example only
zpk.z1 = 456.7f; // example only
DCL_REQUEST_UPDATE(&pi);
DCL_updatePI(&pi);
...

You could also place a call to DCL_updatePI in your background loop if you intend to make manual adjustments to the controller parameters later. Section 2.4 in the DCL user's guide provides more information on this topic. I hope this helps.

Regards,

Richard

Hi Richard,

Thank you for your clear explanation. It is really helpful. I'm new at c2000 and I kindly request you to review my work after your message. I explained my approach and why I needed ZPK3 format.

APPROACH 1. I'm designing a digitally controlled buck converter (VMC). For control loop parameters, I used small signal models of converter and by using sisotool I designed a compansator in series form PI controller in s-domain. 

Now, I need to reflect them to software.

Then, I thought that both software side (DCL PI C1) and s-domain compensator (PI Compensator) side have same structure. Therefore, my s-domain designed compensator will show same performance at software also. My s-domain compensator bandwidth is 0.01*fsw. ISR loop interrupt frequency and mosfet switching frequency (fsw) are all same. As a result, I thought that I can directly use s-domain PI parameters, Kp and Ki can DIRECTLY be used at my digital DCL PI C1.

Could you please comment on wrong phases of my approach?

APPROACH 2. After reading SPRAAB3 application, I noticed that direct digital design approach shows better performance than my above approach. Because at above approach, I didn’t take the system delay which reduces my phase margin. Therefore, I digitalized my plant and again by using sisotool. I obtained a digital PI controller parameters as a format of below.

Now, I need to reflect them to software.

As I read from DCL user guide, “ZPK3” structure enables direct form compensators to be configured from specifications involving pole and zero frequencies.

I thought that by using ZPK3 format I can directly use my z-domain compensator transfer function shown above and by multiplying it with error signal I could observe compensated signal...

However, as I understood from your above exp., ZPK3 just helps me to form my real DCL PI C1 (Series PI function) and changes PI parameters according to format. I again will go on using run DCL_runPI_C1 function to use digital PI controller at my ISR. And therefore, that I previously used Kp and Ki parameters should be commented out because I will use ZPK3 format now in order to form series PI.

Is my explanation correct?

void main(void)

{

   pi_cur.Kp = 10.0f;         //!< Proportional gain

   pi_cur.Ki = 1.0f;           //!< Integral gain

   pi_cur.i10 = 0.0f;         //!< I storage

   pi_cur.Umax = max_duty;     //!< Upper control saturation limit

   pi_cur.Umin = 0.0f;         //!< Lower control saturation limit

   pi_cur.i6 = 1.0f;           //!< Saturation storage

   pi_cur.i11 = 0.0f;         //!< I storage

   pi_cur.Imax = 1.0f;         //!< Upper integrator saturation limit

   pi_cur.Imin = 1.0f;         //!< Lower integrator saturation limit

}

a. The ZPK3 formated PI will show better performance (phase margin) than normal use of DCL PI C1 with Kp and Ki parameter etc. Is it correct?

b. Is SAMPLE RATE same with my interrupt frequency or clock of CPU or control loop bandwidth frequency?

c. I couldn’t see that you inserted “DCL_loadParallelPIasZPK” function at your above code. By the way, DCL PI C1 is series form PI, why you didn’t offer “DCL_loadSeriesPIasZPK”.

I'm sorry for taking your time on same topic.

Richard,

I got all points thank you.

Dear Richard,

I tried to convert my DCL PI C1 to zpk formated PI a below, however I got errors could you please review?

1. I just commented out Kp and Ki lines, and inserted DCL_loadSeriesPIasZPK. Because I still want to use Umax and Umin etc.. Could you please correct me also?

2.How can I solve the errors?

My code is below, it is cleared by deleting some parts.

#include "F28x_Project.h"
#include "DCLF32.h"

//
//=====================================
// Function Protoypes
//

interrupt void CNTL_ISR(void); //EPWM 3 is used to trigger CNTL ISR when TBCTR=CMPB

//===================================== DCL =====================================//
// Sampling Rate Definitions for ZPK Formated PI Controller
//
#define SAMPLE_RATE 5000.0f;
#define SAMPLE_PERIOD 1.0f/SAMPLE_RATE; //ZPK Format, C2D Transformation Sampling Time

DCL_PI pi_cur = PI_DEFAULTS; //It is to be called at ISR

DCL_PI_SPS pi_sps_cur = PI_SPS_DEFAULTS;
DCL_CSS pi_css_cur = DCL_CSS_DEFAULTS;
DCL_ZPK3 zpk_cur = ZPK3_DEFAULTS;

float32_t uk; // OUTPUT of Current loop PI Control Output
float32_t rk = 15.0f; // REFERRENCE of Current loop PI Control Reference
float32_t yk; // FEEDBACK of Current loop PI Control Reference

void main(void)
{

//
//=====================================
// DCL Initialize Controller Structs
//

pi_cur.sps = &pi_sps_cur;
pi_cur.css = &pi_css_cur;
DCL_SET_CONTROLLER_PERIOD(&pi_cur,SAMPLE_PERIOD);

//
//=====================================
// DCL control variables
//
//pi_cur.Kp = 10.0f; //!< Proportional gain (Commented because ZPK format to be used)
//pi_cur.Ki = 1.0f; //!< Integral gain (Commented because ZPK format to be used)
DCL_loadSeriesPIasZPK(&pi_cur,&zpk_cur); //Loads the SPS coefficients to form series form PI controller
zpk_cur.K = 10.0f; // example only
zpk_cur.z1 = 1.0f; // example only
pi_cur.i10 = 0.0f; //!< I storage
pi_cur.Umax = max_duty; //!< Upper control saturation limit
pi_cur.Umin = 0.0f; //!< Lower control saturation limit
pi_cur.i6 = 1.0f; //!< Saturation storage
pi_cur.i11 = 0.0f; //!< I storage
pi_cur.Imax = 1.0f; //!< Upper integrator saturation limit
pi_cur.Imin = 1.0f; //!< Lower integrator saturation limit
DCL_REQUEST_UPDATE(&pi_cur);
DCL_updatePI(&pi_cur);

do {

GpioDataRegs.GPADAT.bit.GPIO31 = 0; // Turn on LED
DELAY_US(1000*500);

} while(1);

}

interrupt void CNTL_ISR(void)
{
uk = DCL_runPI_C1(&pi_cur, rk, yk); // Takes 52 cycle
EPwm1Regs.CMPA.bit.CMPA = period * uk; // Load New Duty Cycle

// Return from interrupt
EPwm3Regs.ETCLR.bit.INT=1; //Enable INT Flag to Enable Further Interrupts
PieCtrlRegs.PIEACK.all = PIEACK_GROUP3; // Acknowledge PIE group 3 to enable further interrupts
}

// end of file

You need to remove the semi-colons from the two #defines.  You should have:

#define SAMPLE_RATE 5000.0f
#define SAMPLE_PERIOD 1.0f/SAMPLE_RATE

I can't see anything obvious in the rest of the code.

Regards,

Richard

Dear Richard,

Thank you for your answer.

I removed semicoloumns at above code but I got now following errros. I generally cannot understand where the error is on usin CSS.

Dear Richard,

I appreciated your detailed and clear explanations. My problem is solved.

Thank you for your effort.

You are welcome!  Glad to know it's working.

Regards,

Richard