一个pid的简单实现

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

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

#include <math.h>

#include "PID.h"
#include <AP_HAL/AP_HAL.h>
#include <AP_Math/AP_Math.h>

extern const AP_HAL::HAL& hal;

const AP_Param::GroupInfo PID::var_info[] = {

// @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, 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, 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, PID, _kd, 0),

// @Param: IMAX
// @DisplayName: PID Integral Maximum
// @Description: The maximum/minimum value that the I term can output
AP_GROUPINFO("IMAX", 3, PID, _imax, 0),

AP_GROUPEND
};

float PID::get_pid(float error, float scaler)
{
uint32_t tnow = AP_HAL::millis();
uint32_t dt = tnow - _last_t;
float output            = 0;
float delta_time;

if (_last_t == 0 || dt > 1000) {
dt = 0;

// if this PID hasn't been used for a full second then zero
// the intergator term. This prevents I buildup from a
// previous fight mode from causing a massive return before
// the integrator gets a chance to correct itself
reset_I();
}
_last_t = tnow;

delta_time = (float)dt / 1000.0f;

// Compute proportional component
output += error * _kp;

// Compute derivative component if time has elapsed
if ((fabsf(_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 {
derivative = (error - _last_error) / delta_time;
}

// discrete low pass filter, cuts out the
// high frequency noise that can drive the controller crazy
float RC = 1/(2*M_PI*_fCut);
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 ((fabsf(_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;
}

int16_t PID::get_pid_4500(float error, float scaler)
{
float v = get_pid(error, scaler);
return constrain_float(v, -4500, 4500);
}

void
PID::reset_I()
{
_integrator = 0;
// we use NAN (Not A Number) to indicate that the last
// derivative value is not valid
_last_derivative = NAN;
}

void
PID::load_gains()
{
_kp.load();
_ki.load();
_kd.load();
_imax.load();
}

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