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/****************************************************************************
*
* Copyright (C) 2013 PX4 Development Team. All rights reserved.
* Author: Anton Babushkin <anton.babushkin@me.com>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name PX4 nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/**
* @file thrust_pid.c
*
* Implementation of thrust control PID.
*
* @author Anton Babushkin <anton.babushkin@me.com>
*/
#include "thrust_pid.h"
#include <math.h>
__EXPORT void thrust_pid_init(thrust_pid_t *pid, float kp, float ki, float kd, float limit_min, float limit_max, uint8_t mode, float dt_min)
{
pid->kp = kp;
pid->ki = ki;
pid->kd = kd;
pid->limit_min = limit_min;
pid->limit_max = limit_max;
pid->mode = mode;
pid->dt_min = dt_min;
pid->last_output = 0.0f;
pid->sp = 0.0f;
pid->error_previous = 0.0f;
pid->integral = 0.0f;
}
__EXPORT int thrust_pid_set_parameters(thrust_pid_t *pid, float kp, float ki, float kd, float limit_min, float limit_max)
{
int ret = 0;
if (isfinite(kp)) {
pid->kp = kp;
} else {
ret = 1;
}
if (isfinite(ki)) {
pid->ki = ki;
} else {
ret = 1;
}
if (isfinite(kd)) {
pid->kd = kd;
} else {
ret = 1;
}
if (isfinite(limit_min)) {
pid->limit_min = limit_min;
} else {
ret = 1;
}
if (isfinite(limit_max)) {
pid->limit_max = limit_max;
} else {
ret = 1;
}
return ret;
}
__EXPORT float thrust_pid_calculate(thrust_pid_t *pid, float sp, float val, float dt, float r22)
{
/* Alternative integral component calculation
*
* start:
* error = setpoint - current_value
* integral = integral + (Ki * error * dt)
* derivative = (error - previous_error) / dt
* previous_error = error
* output = (Kp * error) + integral + (Kd * derivative)
* wait(dt)
* goto start
*/
if (!isfinite(sp) || !isfinite(val) || !isfinite(dt)) {
return pid->last_output;
}
float i, d;
pid->sp = sp;
// Calculated current error value
float error = pid->sp - val;
// Calculate or measured current error derivative
if (pid->mode == THRUST_PID_MODE_DERIVATIV_CALC) {
d = (error - pid->error_previous) / fmaxf(dt, pid->dt_min);
pid->error_previous = error;
} else if (pid->mode == THRUST_PID_MODE_DERIVATIV_CALC_NO_SP) {
d = (-val - pid->error_previous) / fmaxf(dt, pid->dt_min);
pid->error_previous = -val;
} else {
d = 0.0f;
}
if (!isfinite(d)) {
d = 0.0f;
}
/* calculate the error integral */
i = pid->integral + (pid->ki * error * dt);
/* attitude-thrust compensation
* r22 is (2, 2) componet of rotation matrix for current attitude */
float att_comp;
if (r22 > 0.8f)
att_comp = 1.0f / r22;
else if (r22 > 0.0f)
att_comp = ((1.0f / 0.8f - 1.0f) / 0.8f) * r22 + 1.0f;
else
att_comp = 1.0f;
/* calculate output */
float output = ((error * pid->kp) + i + (d * pid->kd)) * att_comp;
/* check for saturation */
if (output < pid->limit_min || output > pid->limit_max) {
/* saturated, recalculate output with old integral */
output = (error * pid->kp) + pid->integral + (d * pid->kd);
} else {
if (isfinite(i)) {
pid->integral = i;
}
}
if (isfinite(output)) {
if (output > pid->limit_max) {
output = pid->limit_max;
} else if (output < pid->limit_min) {
output = pid->limit_min;
}
pid->last_output = output;
}
return pid->last_output;
}
__EXPORT void thrust_pid_set_integral(thrust_pid_t *pid, float i)
{
pid->integral = i;
}
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