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/**
* Copyright 2017 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "pid.hpp"
namespace ec
{
/********************************
* clamp
*
*/
static float clamp(float x, float min, float max)
{
if (x < min)
{
return min;
}
else if (x > max)
{
return max;
}
return x;
}
/********************************
* pid code
* Note: Codes assumes the ts field is non-zero
*/
float pid(pid_info_t* pidinfoptr, float input, float setpoint)
{
float error;
float p_term = 0.0f;
float i_term = 0.0f;
float ff_term = 0.0f;
float output;
// calculate P, I, D, FF
// Pid
error = setpoint - input;
p_term = pidinfoptr->p_c * error;
// pId
if (0.0f != pidinfoptr->i_c)
{
i_term = pidinfoptr->integral;
i_term += error * pidinfoptr->i_c * pidinfoptr->ts;
i_term = clamp(i_term, pidinfoptr->i_lim.min, pidinfoptr->i_lim.max);
}
// FF
ff_term = (setpoint + pidinfoptr->ff_off) * pidinfoptr->ff_gain;
output = p_term + i_term + ff_term;
output = clamp(output, pidinfoptr->out_lim.min, pidinfoptr->out_lim.max);
// slew rate
// TODO(aarena) - Simplify logic as Andy suggested by creating dynamic
// out_lim_min/max that are affected by slew rate control and just clamping
// to those instead of effectively clamping twice.
if (pidinfoptr->initialized)
{
if (pidinfoptr->slew_neg != 0.0f)
{
// Don't decrease too fast
float min_out = pidinfoptr->last_output + pidinfoptr->slew_neg *
pidinfoptr->ts;
if (output < min_out)
{
output = min_out;
}
}
if (pidinfoptr->slew_pos != 0.0f)
{
// Don't increase too fast
float max_out = pidinfoptr->last_output + pidinfoptr->slew_pos *
pidinfoptr->ts;
if (output > max_out)
{
output = max_out;
}
}
if (pidinfoptr->slew_neg != 0.0f || pidinfoptr->slew_pos != 0.0f)
{
// Back calculate integral term for the cases where we limited the
// output
i_term = output - p_term;
}
}
// Clamp again because having limited the output may result in a
// larger integral term
i_term = clamp(i_term, pidinfoptr->i_lim.min, pidinfoptr->i_lim.max);
pidinfoptr->integral = i_term;
pidinfoptr->initialized = true;
pidinfoptr->last_output = output;
return output;
}
}