ardupilot/libraries/AC_PID/AC_PID.cpp

142 lines
3.6 KiB
C++

// -*- 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"
// Examples for _filter:
// f_cut = 10 Hz -> _filter = 15.9155e-3
// f_cut = 15 Hz -> _filter = 10.6103e-3
// f_cut = 20 Hz -> _filter = 7.9577e-3
// f_cut = 25 Hz -> _filter = 6.3662e-3
// f_cut = 30 Hz -> _filter = 5.3052e-3
const float AC_PID::_filter = 7.9577e-3; // Set to "1 / ( 2 * PI * f_cut )";
const AP_Param::GroupInfo AC_PID::var_info[] PROGMEM = {
// @Param: P
// @DisplayName: PID Proportional Gain
// @Description: P Gain which produces an output value that is proportional to the current error value
AP_GROUPINFO("P", 0, AC_PID, _kp, 0),
// @Param: I
// @DisplayName: PID Integral Gain
// @Description: I Gain which produces an output that is proportional to both the magnitude and the duration of the error
AP_GROUPINFO("I", 1, AC_PID, _ki, 0),
// @Param: D
// @DisplayName: PID Derivative Gain
// @Description: D Gain which produces an output that is proportional to the rate of change of the error
AP_GROUPINFO("D", 2, AC_PID, _kd, 0),
// @Param: IMAX
// @DisplayName: PID Integral Maximum
// @Description: The maximum/minimum value that the I term can output
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;
}
// This is an integrator which tends to decay to zero naturally
// if the error is zero.
int32_t AC_PID::get_leaky_i(int32_t error, float dt, float leak_rate)
{
if((_ki != 0) && (dt != 0)){
_integrator -= (float)_integrator * leak_rate;
_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)) {
float derivative;
if (isnan(_last_derivative)) {
// we've just done a reset, suppress the first derivative
// term as we don't want a sudden change in input to cause
// a large D output change
derivative = 0;
_last_derivative = 0;
} else {
// calculate instantaneous derivative
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);
}
void
AC_PID::reset_I()
{
_integrator = 0;
// mark derivative as invalid
_last_derivative = NAN;
}
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();
}