mirror of https://github.com/ArduPilot/ardupilot
142 lines
3.6 KiB
C++
142 lines
3.6 KiB
C++
// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-
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/// @file AC_PID.cpp
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/// @brief Generic PID algorithm
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#include <math.h>
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#include "AC_PID.h"
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// Examples for _filter:
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// f_cut = 10 Hz -> _filter = 15.9155e-3
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// f_cut = 15 Hz -> _filter = 10.6103e-3
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// f_cut = 20 Hz -> _filter = 7.9577e-3
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// f_cut = 25 Hz -> _filter = 6.3662e-3
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// f_cut = 30 Hz -> _filter = 5.3052e-3
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const float AC_PID::_filter = 7.9577e-3; // Set to "1 / ( 2 * PI * f_cut )";
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const AP_Param::GroupInfo AC_PID::var_info[] PROGMEM = {
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// @Param: P
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// @DisplayName: PID Proportional Gain
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// @Description: P Gain which produces an output value that is proportional to the current error value
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AP_GROUPINFO("P", 0, AC_PID, _kp, 0),
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// @Param: I
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// @DisplayName: PID Integral Gain
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// @Description: I Gain which produces an output that is proportional to both the magnitude and the duration of the error
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AP_GROUPINFO("I", 1, AC_PID, _ki, 0),
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// @Param: D
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// @DisplayName: PID Derivative Gain
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// @Description: D Gain which produces an output that is proportional to the rate of change of the error
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AP_GROUPINFO("D", 2, AC_PID, _kd, 0),
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// @Param: IMAX
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// @DisplayName: PID Integral Maximum
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// @Description: The maximum/minimum value that the I term can output
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AP_GROUPINFO("IMAX", 3, AC_PID, _imax, 0),
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AP_GROUPEND
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};
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int32_t AC_PID::get_p(int32_t error)
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{
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return (float)error * _kp;
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}
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int32_t AC_PID::get_i(int32_t error, float dt)
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{
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if((_ki != 0) && (dt != 0)) {
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_integrator += ((float)error * _ki) * dt;
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if (_integrator < -_imax) {
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_integrator = -_imax;
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} else if (_integrator > _imax) {
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_integrator = _imax;
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}
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return _integrator;
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}
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return 0;
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}
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// This is an integrator which tends to decay to zero naturally
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// if the error is zero.
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int32_t AC_PID::get_leaky_i(int32_t error, float dt, float leak_rate)
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{
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if((_ki != 0) && (dt != 0)){
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_integrator -= (float)_integrator * leak_rate;
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_integrator += ((float)error * _ki) * dt;
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if (_integrator < -_imax) {
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_integrator = -_imax;
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} else if (_integrator > _imax) {
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_integrator = _imax;
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}
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return _integrator;
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}
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return 0;
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}
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int32_t AC_PID::get_d(int32_t input, float dt)
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{
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if ((_kd != 0) && (dt != 0)) {
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float derivative;
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if (isnan(_last_derivative)) {
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// we've just done a reset, suppress the first derivative
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// term as we don't want a sudden change in input to cause
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// a large D output change
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derivative = 0;
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_last_derivative = 0;
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} else {
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// calculate instantaneous derivative
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derivative = (input - _last_input) / dt;
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}
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// discrete low pass filter, cuts out the
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// high frequency noise that can drive the controller crazy
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derivative = _last_derivative +
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(dt / ( _filter + dt)) * (derivative - _last_derivative);
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// update state
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_last_input = input;
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_last_derivative = derivative;
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// add in derivative component
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return _kd * derivative;
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}
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return 0;
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}
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int32_t AC_PID::get_pi(int32_t error, float dt)
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{
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return get_p(error) + get_i(error, dt);
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}
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int32_t AC_PID::get_pid(int32_t error, float dt)
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{
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return get_p(error) + get_i(error, dt) + get_d(error, dt);
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}
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void
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AC_PID::reset_I()
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{
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_integrator = 0;
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// mark derivative as invalid
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_last_derivative = NAN;
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}
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void
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AC_PID::load_gains()
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{
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_kp.load();
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_ki.load();
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_kd.load();
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_imax.load();
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_imax = abs(_imax);
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}
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void
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AC_PID::save_gains()
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{
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_kp.save();
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_ki.save();
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_kd.save();
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_imax.save();
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}
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