pid.cpp

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/****************************************************************************
 *
 *   Copyright (C) 2008-2013 PX4 Development Team. All rights reserved.
 *   Author: Laurens Mackay <mackayl@student.ethz.ch>
 *           Tobias Naegeli <naegelit@student.ethz.ch>
 *           Martin Rutschmann <rutmarti@student.ethz.ch>
 *           Anton Babushkin <anton.babushkin@me.com>
 *           Julian Oes <joes@student.ethz.ch>
 *
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 * modification, are permitted provided that the following conditions
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 *    the documentation and/or other materials provided with the
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/**
 * @file pid.c
 *
 * Implementation of generic PID controller.
 *
 * @author Laurens Mackay <mackayl@student.ethz.ch>
 * @author Tobias Naegeli <naegelit@student.ethz.ch>
 * @author Martin Rutschmann <rutmarti@student.ethz.ch>
 * @author Anton Babushkin <anton.babushkin@me.com>
 * @author Julian Oes <joes@student.ethz.ch>
 */

#include "pid.h"
#include <math.h>
#include <px4_platform_common/defines.h>

#define SIGMA 0.000001f

__EXPORT void pid_init(PID_t *pid, pid_mode_t mode, float dt_min)
{
    pid->mode = mode;
    pid->dt_min = dt_min;
    pid->kp = 0.0f;
    pid->ki = 0.0f;
    pid->kd = 0.0f;
    pid->integral = 0.0f;
    pid->integral_limit = 0.0f;
    pid->output_limit = 0.0f;
    pid->error_previous = 0.0f;
    pid->last_output = 0.0f;
}

__EXPORT int pid_set_parameters(PID_t *pid, float kp, float ki, float kd, float integral_limit, float output_limit)
{
    int ret = 0;

    if (PX4_ISFINITE(kp)) {
        pid->kp = kp;

    } else {
        ret = 1;
    }

    if (PX4_ISFINITE(ki)) {
        pid->ki = ki;

    } else {
        ret = 1;
    }

    if (PX4_ISFINITE(kd)) {
        pid->kd = kd;

    } else {
        ret = 1;
    }

    if (PX4_ISFINITE(integral_limit)) {
        pid->integral_limit = integral_limit;

    }  else {
        ret = 1;
    }

    if (PX4_ISFINITE(output_limit)) {
        pid->output_limit = output_limit;

    }  else {
        ret = 1;
    }

    return ret;
}

__EXPORT float pid_calculate(PID_t *pid, float sp, float val, float val_dot, float dt)
{
    if (!PX4_ISFINITE(sp) || !PX4_ISFINITE(val) || !PX4_ISFINITE(val_dot) || !PX4_ISFINITE(dt)) {
        return pid->last_output;
    }

    float i, d;

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

    /* current error derivative */
    if (pid->mode == PID_MODE_DERIVATIV_CALC) {
        d = (error - pid->error_previous) / fmaxf(dt, pid->dt_min);
        pid->error_previous = error;

    } else if (pid->mode == PID_MODE_DERIVATIV_CALC_NO_SP) {
        d = (-val - pid->error_previous) / fmaxf(dt, pid->dt_min);
        pid->error_previous = -val;

    } else if (pid->mode == PID_MODE_DERIVATIV_SET) {
        d = -val_dot;

    } else {
        d = 0.0f;
    }

    if (!PX4_ISFINITE(d)) {
        d = 0.0f;
    }

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

    if (pid->ki > SIGMA) {
        // Calculate the error integral and check for saturation
        i = pid->integral + (error * dt);

        /* check for saturation */
        if (PX4_ISFINITE(i)) {
            if ((pid->output_limit < SIGMA || (fabsf(output + (i * pid->ki)) <= pid->output_limit)) &&
                fabsf(i) <= pid->integral_limit) {
                /* not saturated, use new integral value */
                pid->integral = i;
            }
        }

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

    /* limit output */
    if (PX4_ISFINITE(output)) {
        if (pid->output_limit > SIGMA) {
            if (output > pid->output_limit) {
                output = pid->output_limit;

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

        pid->last_output = output;
    }

    return pid->last_output;
}


__EXPORT void pid_reset_integral(PID_t *pid)
{
    pid->integral = 0.0f;
}