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pid.c File Reference


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.

Author:
Atmel Corporation: http://www.atmel.com
Support email: avr@atmel.com
Name
RELEASE_1_0
Revision
1.1
RCSfile
pid.c,v
Date
2006/02/16 11:46:13

Definition in file pid.c.

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

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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.


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, int16_t, int32_t, 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().

00060 { 00061 int16_t error, p_term, d_term; 00062 int32_t i_term, ret, temp; 00063 00064 error = setPoint - processValue; 00065 00066 // Calculate Pterm and limit error overflow 00067 if (error > pid_st->maxError){ 00068 p_term = MAX_INT; 00069 } 00070 else if (error < -pid_st->maxError){ 00071 p_term = -MAX_INT; 00072 } 00073 else{ 00074 p_term = pid_st->P_Factor * error; 00075 } 00076 00077 // Calculate Iterm and limit integral runaway 00078 temp = pid_st->sumError + error; 00079 if(temp > pid_st->maxSumError){ 00080 i_term = MAX_I_TERM; 00081 pid_st->sumError = pid_st->maxSumError; 00082 } 00083 else if(temp < -pid_st->maxSumError){ 00084 i_term = -MAX_I_TERM; 00085 pid_st->sumError = -pid_st->maxSumError; 00086 } 00087 else{ 00088 pid_st->sumError = temp; 00089 i_term = pid_st->I_Factor * pid_st->sumError; 00090 } 00091 00092 // Calculate Dterm 00093 d_term = pid_st->D_Factor * (pid_st->lastProcessValue - processValue); 00094 00095 pid_st->lastProcessValue = processValue; 00096 00097 ret = (p_term + i_term + d_term) / SCALING_FACTOR; 00098 if(ret > MAX_INT){ 00099 ret = MAX_INT; 00100 } 00101 else if(ret < -MAX_INT){ 00102 ret = -MAX_INT; 00103 } 00104 00105 return((int16_t)ret); 00106 }

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().

00037 { 00038 // Start values for PID controller 00039 pid->sumError = 0; 00040 pid->lastProcessValue = 0; 00041 // Tuning constants for PID loop 00042 pid->P_Factor = p_factor; 00043 pid->I_Factor = i_factor; 00044 pid->D_Factor = d_factor; 00045 // Limits to avoid overflow 00046 pid->maxError = MAX_INT / (pid->P_Factor + 1); 00047 pid->maxSumError = MAX_I_TERM / (pid->I_Factor + 1); 00048 }

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 pidData_t, and PID_DATA::sumError.

00113 { 00114 pid_st->sumError = 0; 00115 }


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