ardupilot/libraries/AC_PID/AC_PID.cpp

// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-

/// @file	AC_PID.cpp
/// @brief	Generic PID algorithm

#include <math.h>
#include "AC_PID.h"

const AP_Param::GroupInfo AC_PID::var_info[] PROGMEM = {
    AP_GROUPINFO("P",    0, AC_PID, _kp, 0),
    AP_GROUPINFO("I",    1, AC_PID, _ki, 0),
    AP_GROUPINFO("D",    2, AC_PID, _kd, 0),
    AP_GROUPINFO("IMAX", 3, AC_PID, _imax, 0),
    AP_GROUPEND
};

int32_t AC_PID::get_p(int32_t error)
{
    return (float)error * _kp;
}

int32_t AC_PID::get_i(int32_t error, float dt)
{
    if((_ki != 0) && (dt != 0)) {
        _integrator += ((float)error * _ki) * dt;
        if (_integrator < -_imax) {
            _integrator = -_imax;
        } else if (_integrator > _imax) {
            _integrator = _imax;
        }
        return _integrator;
    }
    return 0;
}

int32_t AC_PID::get_d(int32_t input, float dt)
{
    if ((_kd != 0) && (dt != 0)) {
        _derivative = (input - _last_input) / dt;

        // discrete low pass filter, cuts out the
        // high frequency noise that can drive the controller crazy
        _derivative = _last_derivative +
                      (dt / ( _filter + dt)) * (_derivative - _last_derivative);

        // update state
        _last_input             = input;
        _last_derivative    = _derivative;

        // add in derivative component
        return _kd * _derivative;
    }
    return 0;
}

int32_t AC_PID::get_pi(int32_t error, float dt)
{
    return get_p(error) + get_i(error, dt);
}


int32_t AC_PID::get_pid(int32_t error, float dt)
{
    return get_p(error) + get_i(error, dt) + get_d(error, dt);
}



/*
 *  int32_t AC_PID::get_pid(int32_t error, float dt)
 *  {
 *       // Compute proportional component
 *       _output = error * _kp;
 *
 *       // Compute derivative component if time has elapsed
 *       if ((fabs(_kd) > 0) && (dt > 0)) {
 *               _derivative = (error - _last_error) / dt;
 *
 *               // discrete low pass filter, cuts out the
 *               // high frequency noise that can drive the controller crazy
 *               _derivative = _last_derivative +
 *                       (dt / ( _filter + dt)) * (_derivative - _last_derivative);
 *
 *               // update state
 *               _last_error        = error;
 *               _last_derivative    = _derivative;
 *
 *               // add in derivative component
 *               _output    += _kd * _derivative;
 *       }
 *
 *       // Compute integral component if time has elapsed
 *       if ((fabs(_ki) > 0) && (dt > 0)) {
 *               _integrator        += (error * _ki) * dt;
 *               if (_integrator < -_imax) {
 *                       _integrator = -_imax;
 *               } else if (_integrator > _imax) {
 *                       _integrator = _imax;
 *               }
 *               _output    += _integrator;
 *       }
 *
 *       return _output;
 *  }
 */


void
AC_PID::reset_I()
{
    _integrator = 0;
    _last_input = 0;
    _last_derivative = 0;
}

void
AC_PID::load_gains()
{
    _kp.load();
    _ki.load();
    _kd.load();
    _imax.load();
    _imax = abs(_imax);
}

void
AC_PID::save_gains()
{
    _kp.save();
    _ki.save();
    _kd.save();
    _imax.save();
}