ardupilot/libraries/PID/PID.cpp

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// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-
/// @file PID.cpp
/// @brief Generic PID algorithm
#include <math.h>
#include "PID.h"
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const AP_Param::GroupInfo PID::var_info[] PROGMEM = {
AP_GROUPINFO("P", PID, _kp),
AP_GROUPINFO("I", PID, _ki),
AP_GROUPINFO("D", PID, _kd),
AP_GROUPINFO("IMAX", PID, _imax),
AP_GROUPEND
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};
long
PID::get_pid(int32_t error, uint16_t dt, float scaler)
{
float output = 0;
float delta_time = (float)dt / 1000.0;
// Compute proportional component
output += error * _kp;
// Compute derivative component if time has elapsed
if ((fabs(_kd) > 0) && (dt > 0)) {
float derivative = (error - _last_error) / delta_time;
// discrete low pass filter, cuts out the
// high frequency noise that can drive the controller crazy
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float RC = 1/(2*M_PI*20);
derivative = _last_derivative +
(delta_time / (RC + delta_time)) * (derivative - _last_derivative);
// update state
_last_error = error;
_last_derivative = derivative;
// add in derivative component
output += _kd * derivative;
}
// scale the P and D components
output *= scaler;
// Compute integral component if time has elapsed
if ((fabs(_ki) > 0) && (dt > 0)) {
_integrator += (error * _ki) * scaler * delta_time;
if (_integrator < -_imax) {
_integrator = -_imax;
} else if (_integrator > _imax) {
_integrator = _imax;
}
output += _integrator;
}
return output;
}
void
PID::reset_I()
{
_integrator = 0;
_last_error = 0;
_last_derivative = 0;
}
void
PID::load_gains()
{
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_kp.load();
_ki.load();
_kd.load();
}
void
PID::save_gains()
{
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_kp.save();
_ki.save();
_kd.save();
}