_pid_.h File Reference

Header file for pid.c. More...

#include "stdint.h"

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Classes
struct	PID_DATA
	PID Status. More...

Macros
#define	SCALING_FACTOR   128
#define	MAX_INT   INT16_MAX
	Maximum values. More...
#define	MAX_LONG   INT32_MAX
#define	MAX_I_TERM   (MAX_LONG / 2)
#define	FALSE   0
#define	TRUE   1

Typedefs
typedef struct PID_DATA	pidData_t
	PID Status. More...

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

Variables
volatile uint8_t	flag

Detailed Description

Header file for pid.c.

• File: pid.h
• Compiler: GCC-AVR
• Supported devices: Tested on 328p
• AppNote: Discrete PID controller

Author

Swarm robot graduation project workgroub
Mechatronics Program for the Distinguished
$Name$

Revision

456

$RCSfile$

Date

021

Definition in file _pid_.h.

Macro Definition Documentation

MAX_INT

#define MAX_INT   INT16_MAX

Maximum values.

Needed to avoid sign/overflow problems

Typedef Documentation

pidData_t

typedef struct PID_DATA pidData_t

PID Status.

Setpoints and data used by the PID control algorithm

Function Documentation

pid_Controller()

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.

{
  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);
}

References MAX_INT, PID_DATA::maxError, PID_DATA::maxSumError, PID_DATA::P_Factor, and PID_DATA::sumError.

Referenced by _update_controller().

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pid_Init()

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.

{
  // 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);
}

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

Referenced by _init_dc_control().

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pid_Reset_Integrator()

void pid_Reset_Integrator

(

pidData_t *

pid_st

)

Resets the integrator.

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

{
  pid_st->sumError = 0;
}

References PID_DATA::sumError.