PX4-Autopilot/src/modules/multirotor_pos_control/thrust_pid.c

/****************************************************************************
 *
 *   Copyright (C) 2013 PX4 Development Team. All rights reserved.
 *   Author: Anton Babushkin <anton.babushkin@me.com>
 *
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/**
 * @file thrust_pid.c
 *
 * Implementation of thrust control PID.
 *
 * @author Anton Babushkin <anton.babushkin@me.com>
 */

#include "thrust_pid.h"
#include <math.h>

#define COS_TILT_MAX	0.7f

__EXPORT void thrust_pid_init(thrust_pid_t *pid, float dt_min)
{
	pid->dt_min = dt_min;
	pid->kp = 0.0f;
	pid->ki = 0.0f;
	pid->kd = 0.0f;
	pid->integral = 0.0f;
	pid->output_min = 0.0f;
	pid->output_max = 0.0f;
	pid->error_previous = 0.0f;
	pid->last_output = 0.0f;
}

__EXPORT int thrust_pid_set_parameters(thrust_pid_t *pid, float kp, float ki, float kd, float output_min, float output_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(output_min)) {
		pid->output_min = output_min;

	}  else {
		ret = 1;
	}

	if (isfinite(output_max)) {
		pid->output_max = output_max;

	}  else {
		ret = 1;
	}

	return ret;
}

__EXPORT float thrust_pid_calculate(thrust_pid_t *pid, float sp, float val, float dt, float r22)
{
	if (!isfinite(sp) || !isfinite(val) || !isfinite(dt)) {
		return pid->last_output;
	}

	float i, d;

	/* error value */
	float error = sp - val;

	/* error derivative */
	d = (-val - pid->error_previous) / fmaxf(dt, pid->dt_min);
	pid->error_previous = -val;

	if (!isfinite(d)) {
		d = 0.0f;
	}

	/* calculate the error integral */
	i = pid->integral + (pid->ki * error * dt);

	/* attitude-thrust compensation
	 * r22 is (2, 2) component of rotation matrix for current attitude */
	float att_comp;

	if (r22 > COS_TILT_MAX) {
		att_comp = 1.0f / r22;

	} else if (r22 > 0.0f) {
		att_comp = ((1.0f / COS_TILT_MAX - 1.0f) / COS_TILT_MAX) * r22 + 1.0f;

	} else {
		att_comp = 1.0f;
	}

	/* calculate PD output */
	float output = ((error * pid->kp) + (d * pid->kd)) * att_comp;

	/* check for saturation */
	if (isfinite(i)) {
		float i_comp = i * att_comp;
		if ((output + i_comp) >= pid->output_min || (output + i_comp) <= pid->output_max) {
			/* not saturated, use new integral value */
			pid->integral = i;
		}
	}

	/* add I component to output */
	output += pid->integral * att_comp;

	/* limit output */
	if (isfinite(output)) {
		if (output > pid->output_max) {
			output = pid->output_max;

		} else if (output < pid->output_min) {
			output = pid->output_min;
		}

		pid->last_output = output;
	}

	return pid->last_output;
}

__EXPORT void thrust_pid_set_integral(thrust_pid_t *pid, float i)
{
	pid->integral = i;
}