pidcontroller.cpp

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/**
 * pidcontroller.cpp
 * Gigatron motor control Arduino code for PID controller.
 * 
 * @author  Bayley Wang   <bayleyw@mit.edu>
 *
 * @date    2016-01-10    syler   moved to separate .cpp file, header is in classes.h
 *
 **/

#include <Arduino.h>
#include "isr.h"
#include "classes.h"

PIDController::PIDController(long kp, long ki, long kd, long out_max, long out_min) {
  _kp = kp; 
  _ki = ki;
  _kd = kd;
  _last_in = 0;
  _integral = 0;
  _out_max = out_max;
  _out_min = out_min;
}

void PIDController::ResetGains(long kp, long ki, long kd) {
  _kp = kp;
  _ki = ki;
  _kd = kd;
  _last_in = 0;
  _integral = 0;
}

void PIDController::ResetIntegrator() {
  _last_in = 0;
  _integral = 0;
}

int PIDController::Update(int ref, int in) {
  //error = desired - actual
  int error = ref - in;

  //Add the error to the integral term
  _integral += error;

  //Integrator windup limiter: limit integral term to _out_max and _out_min. 
  //If the output command with only the integrator is past the limit, keep it under the limit. 
  long cmd_output = _integral * _ki >> 8;
  if (cmd_output > _out_max) _integral = (_out_max << 8) / _ki; 
  if (cmd_output < _out_min) _integral = (_out_min << 8) / _ki;

  //Get the derivative and save the current value for the next iteration
  int deriv = _last_in - in;
  _last_in = in;
  
  //add the PID terms to the command output
  cmd_output = _ki * _integral + _kp * error + _kd * deriv;

  //This bit shift is necessary for some reason
  cmd_output = cmd_output >> 8; 
  
  //Limit the command output
  if (cmd_output > _out_max) cmd_output = _out_max;
  if (cmd_output < _out_min) cmd_output = _out_min;

  //Return the command output
  return cmd_output;
}