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/****************************************************************************
* pid.c
*
* Copyright (C) 2012 Ivan Ovinnikov. All rights reserved.
* Authors: Ivan Ovinnikov <oivan@ethz.ch>
*
* 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 NuttX 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.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include "pid.h"
#include "fixedwing_control.h"
/*******************************************************************************
* pid()
*
* Calculates the PID control output given an error
*
* Input: float error, uint16_t dt, float scaler, float K_p, float K_i, float K_d
*
* Output: PID control value
*
******************************************************************************/
static float pid(float error, float error_deriv, uint16_t dt, float scaler, float K_p, float K_i, float K_d, float intmax)
{
// PID parameters
float Kp = K_p;
float Ki = K_i;
float Kd = K_d;
float delta_time = dt; // delta time
float lerror; // last error value
float imax = intmax; // max integral value
float integrator;
float derivative;
float lderiv;
int fCut = 20; // anything above 20 Hz is considered noise - low pass filter for the derivative
float output = 0; // the output of the PID controller
output += error * Kp;
if ((fabs(Kd) > 0) && (dt > 0)) {
if (PID_DERIVMODE_CALC) {
derivative = (error - lerror) / 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 = lderiv +
(delta_time / (RC + delta_time)) * (derivative - lderiv);
// update state
lerror = error;
lderiv = derivative;
} else {
derivative = error_deriv;
}
// add in derivative component
output += Kd * derivative;
}
printf("PID derivative %i\n", (int)(1000 * derivative));
// scale the P and D components
output *= scaler;
// Compute integral component if time has elapsed
if ((fabs(Ki) > 0) && (dt > 0)) {
integrator += (error * Ki) * scaler * delta_time;
if (integrator < -imax) {
integrator = -imax;
} else if (integrator > imax) {
integrator = imax;
}
output += integrator;
}
printf("PID Integrator %i\n", (int)(1000 * integrator));
return output;
}
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