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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 pid_control
{
namespace ec
{
/********************************
* clamp
*
*/
static double clamp(double x, double min, double 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
*/
double pid(pid_info_t* pidinfoptr, double input, double setpoint)
{
double error;
double proportionalTerm;
double integralTerm = 0.0f;
double derivativeTerm = 0.0f;
double feedFwdTerm = 0.0f;
double output;
// calculate P, I, D, FF
// Pid
error = setpoint - input;
proportionalTerm = pidinfoptr->proportionalCoeff * error;
// pId
if (0.0f != pidinfoptr->integralCoeff)
{
integralTerm = pidinfoptr->integral;
integralTerm += error * pidinfoptr->integralCoeff * pidinfoptr->ts;
integralTerm = clamp(integralTerm, pidinfoptr->integralLimit.min,
pidinfoptr->integralLimit.max);
}
// piD
derivativeTerm = pidinfoptr->derivativeCoeff *
((error - pidinfoptr->lastError) / pidinfoptr->ts);
// FF
feedFwdTerm =
(setpoint + pidinfoptr->feedFwdOffset) * pidinfoptr->feedFwdGain;
output = proportionalTerm + integralTerm + derivativeTerm + feedFwdTerm;
output = clamp(output, pidinfoptr->outLim.min, pidinfoptr->outLim.max);
// slew rate
// TODO(aarena) - Simplify logic as Andy suggested by creating dynamic
// outLim_min/max that are affected by slew rate control and just clamping
// to those instead of effectively clamping twice.
if (pidinfoptr->initialized)
{
if (pidinfoptr->slewNeg != 0.0f)
{
// Don't decrease too fast
double minOut =
pidinfoptr->lastOutput + pidinfoptr->slewNeg * pidinfoptr->ts;
if (output < minOut)
{
output = minOut;
}
}
if (pidinfoptr->slewPos != 0.0f)
{
// Don't increase too fast
double maxOut =
pidinfoptr->lastOutput + pidinfoptr->slewPos * pidinfoptr->ts;
if (output > maxOut)
{
output = maxOut;
}
}
if (pidinfoptr->slewNeg != 0.0f || pidinfoptr->slewPos != 0.0f)
{
// Back calculate integral term for the cases where we limited the
// output
integralTerm = output - proportionalTerm;
}
}
// Clamp again because having limited the output may result in a
// larger integral term
integralTerm = clamp(integralTerm, pidinfoptr->integralLimit.min,
pidinfoptr->integralLimit.max);
pidinfoptr->integral = integralTerm;
pidinfoptr->initialized = true;
pidinfoptr->lastError = error;
pidinfoptr->lastOutput = output;
return output;
}
} // namespace ec
} // namespace pid_control