mirror of https://github.com/ArduPilot/ardupilot
123 lines
2.9 KiB
C++
123 lines
2.9 KiB
C++
// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-
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/// @file PID.cpp
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/// @brief Generic PID algorithm
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#include <math.h>
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#include "PID.h"
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#include <AP_HAL.h>
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#include <AP_Math.h>
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extern const AP_HAL::HAL& hal;
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const AP_Param::GroupInfo PID::var_info[] PROGMEM = {
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AP_GROUPINFO("P", 0, PID, _kp, 0),
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AP_GROUPINFO("I", 1, PID, _ki, 0),
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AP_GROUPINFO("D", 2, PID, _kd, 0),
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AP_GROUPINFO("IMAX", 3, PID, _imax, 0),
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AP_GROUPEND
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};
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float PID::get_pid(float error, float scaler)
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{
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uint32_t tnow = hal.scheduler->millis();
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uint32_t dt = tnow - _last_t;
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float output = 0;
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float delta_time;
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if (_last_t == 0 || dt > 1000) {
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dt = 0;
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// if this PID hasn't been used for a full second then zero
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// the intergator term. This prevents I buildup from a
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// previous fight mode from causing a massive return before
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// the integrator gets a chance to correct itself
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reset_I();
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}
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_last_t = tnow;
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delta_time = (float)dt / 1000.0f;
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// Compute proportional component
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output += error * _kp;
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// Compute derivative component if time has elapsed
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if ((fabsf(_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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derivative = (error - _last_error) / delta_time;
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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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float RC = 1/(2*PI*_fCut);
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derivative = _last_derivative +
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((delta_time / (RC + delta_time)) *
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(derivative - _last_derivative));
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// update state
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_last_error = error;
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_last_derivative = derivative;
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// add in derivative component
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output += _kd * derivative;
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}
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// scale the P and D components
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output *= scaler;
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// Compute integral component if time has elapsed
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if ((fabsf(_ki) > 0) && (dt > 0)) {
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_integrator += (error * _ki) * scaler * delta_time;
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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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output += _integrator;
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}
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return output;
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}
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int16_t PID::get_pid_4500(float error, float scaler)
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{
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float v = get_pid(error, scaler);
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return constrain(v, -4500, 4500);
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}
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void
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PID::reset_I()
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{
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_integrator = 0;
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// we use NAN (Not A Number) to indicate that the last
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// derivative value is not valid
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_last_derivative = NAN;
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}
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void
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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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}
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void
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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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