File content as of revision 3:27b75e7dd54a:

/*  
    PI Controller class with anti windup reset in biquad transposed direct form 2
    see e.g.: https://www.dsprelated.com/freebooks/filters/Four_Direct_Forms.html
    everything is calculated in double
    
                     Ts         z - 1             
      G(s) = P + I ------- + D -------          D corresponds Kd/Tf in Matlab-formlism pid(...)
                    z - 1       z - p              
*/

#include "PID_Cntrl.h"
using namespace std;

PID_Cntrl::PID_Cntrl(float P, float I, float D, float tau_f, float Ts, float uMin, float uMax)
{
    setCoefficients(P, I, D, tau_f, Ts);
    this->uMin = (double)uMin;
    this->uMax = (double)uMax;
    reset(0.0f);
}

PID_Cntrl::~PID_Cntrl() {}

void PID_Cntrl::reset(float initValue)
{
    Iold = (double)initValue;
    eold = 0.0;yold = 0.0;
    del = 0.0;
}

void PID_Cntrl::setCoefficients(float P, float I, float D, float tau_f, float Ts)
{
    this->p = 1.0 - (double)Ts/(double)tau_f;
    this->P = P;
    this->I = I;
    this->D = D;
    this->Ts = Ts;
    if(P!=0)
        this->Ka=1/P;
    else
        this->Ka=1.0f;
    
}

float PID_Cntrl::doStep(double e)
{
    double Ipart = Iold+I*Ts*(e-del);
    double Dpart = D*(e-eold)+p*yold;
    double u = P*e + Dpart  + Ipart;          // unconstrained output
    double uc = u;                // constrained output
    if(u > uMax) uc = uMax;
    else if(u < uMin) uc = uMin;
    del=(u-uc)*Ka;
    eold=e;
    Iold=Ipart;
    yold=Dpart;
    return (float)uc;
}

void PID_Cntrl::set_limits(double ll, double ul)
{
    this->uMin = (double)ll;
    this->uMax = (double)ul;
}
float PID_Cntrl::get_ulimit(void)
{
    return (float)this->uMax;
}