pid.c File Reference

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Detailed Description

General PID implementation for AVR.

Discrete PID controller implementation. Set up by giving P/I/D terms to Init_PID(), and uses a struct PID_DATA to store internal values.

• File: pid.c
• Compiler: IAR EWAAVR 4.11A
• Supported devices: All AVR devices can be used.
• AppNote: AVR221 - Discrete PID controller

Author:

Atmel Corporation: http://www.atmel.com
Support email: avr@atmel.com

$Name$

Revision

456

$RCSfile$

Date

2006-02-16 12:46:13 +0100 (to, 16 feb 2006)

Definition in file pid.c.

#include "pid.h"
#include "stdint.h"

Include dependency graph for pid.c:

Go to the source code of this file.

Functions
int16_t	pid_Controller (int16_t setPoint, int16_t processValue, struct PID_DATA *pid_st)
	PID control algorithm.
void	pid_Init (int16_t p_factor, int16_t i_factor, int16_t d_factor, struct PID_DATA *pid)
	Initialisation of PID controller parameters.
void	pid_Reset_Integrator (pidData_t *pid_st)
	Resets the integrator.

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Function Documentation

int16_t pid_Controller	(	int16_t	setPoint,
		int16_t	processValue,
		struct PID_DATA *	pid_st
	)

PID control algorithm.

Calculates output from setpoint, process value and PID status.

Parameters:

	setPoint	Desired value.
	processValue	Measured value.
	pid_st	PID status struct.

Definition at line 59 of file pid.c.

References PID_DATA::D_Factor, PID_DATA::I_Factor, PID_DATA::lastProcessValue, MAX_I_TERM, MAX_INT, PID_DATA::maxError, PID_DATA::maxSumError, PID_DATA::P_Factor, SCALING_FACTOR, and PID_DATA::sumError.

Referenced by main().

{
  int16_t error, p_term, d_term;
  int32_t i_term, ret, temp;

  error = setPoint - processValue;

  // Calculate Pterm and limit error overflow
  if (error > pid_st->maxError){
    p_term = MAX_INT;
  }
  else if (error < -pid_st->maxError){
    p_term = -MAX_INT;
  }
  else{
    p_term = pid_st->P_Factor * error;
  }

  // Calculate Iterm and limit integral runaway
  temp = pid_st->sumError + error;
  if(temp > pid_st->maxSumError){
    i_term = MAX_I_TERM;
    pid_st->sumError = pid_st->maxSumError;
  }
  else if(temp < -pid_st->maxSumError){
    i_term = -MAX_I_TERM;
    pid_st->sumError = -pid_st->maxSumError;
  }
  else{
    pid_st->sumError = temp;
    i_term = pid_st->I_Factor * pid_st->sumError;
  }

  // Calculate Dterm
  d_term = pid_st->D_Factor * (pid_st->lastProcessValue - processValue);

  pid_st->lastProcessValue = processValue;

  ret = (p_term + i_term + d_term) / SCALING_FACTOR;
  if(ret > MAX_INT){
    ret = MAX_INT;
  }
  else if(ret < -MAX_INT){
    ret = -MAX_INT;
  }

  return((int16_t)ret);
}

void pid_Init	(	int16_t	p_factor,
		int16_t	i_factor,
		int16_t	d_factor,
		struct PID_DATA *	pid
	)

Initialisation of PID controller parameters.

Initialise the variables used by the PID algorithm.

Parameters:

	p_factor	Proportional term.
	i_factor	Integral term.
	d_factor	Derivate term.
	pid	Struct with PID status.

Definition at line 35 of file pid.c.

References PID_DATA::D_Factor, PID_DATA::I_Factor, PID_DATA::lastProcessValue, MAX_I_TERM, MAX_INT, PID_DATA::maxError, PID_DATA::maxSumError, PID_DATA::P_Factor, and PID_DATA::sumError.

Referenced by Init().

{
  // Start values for PID controller
  pid->sumError = 0;
  pid->lastProcessValue = 0;
  // Tuning constants for PID loop
  pid->P_Factor = p_factor;
  pid->I_Factor = i_factor;
  pid->D_Factor = d_factor;
  // Limits to avoid overflow
  pid->maxError = MAX_INT / (pid->P_Factor + 1);
  pid->maxSumError = MAX_I_TERM / (pid->I_Factor + 1);
}

void pid_Reset_Integrator

(

pidData_t *

pid_st

)

Resets the integrator.

Calling this function will reset the integrator in the PID regulator.

Definition at line 112 of file pid.c.

References PID_DATA::sumError.

{
  pid_st->sumError = 0;
}

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