西门子S7-300 PLC 中如何自己编制PID程序？

首先用fc105模块将第一条的模拟量，二、三条的压力等转换为对应的数字量。然后用这个转换后的数字量作为fb41的参考输入，这样pid会根据这个参考输入（即目标值）计算pid的控制量。然后将此控制量利用fc106转换为模拟量输出给阀门来改变阀门开度即可。

这里面你的问题比较笼统，主要是你进来的模拟量的量程，然后就是你控制阀门的类型，比如说用4-200ma控制阀门，还是1-5v控制阀门，这个还要具体讨论。

fc105

106是模数、数模转换模块。因为plc不能直接处理模拟量，所以要通过模块来转换，如果你要完成具体程序，就要知道你用的模拟量的类型、量程。

另外fb41的背景db你分配后它里面就含有fb41的具体参数，作为一般应用其实可以不用通过背景db来编程。用梯形图基本就可以处理你的问题。

BC31 TC30 编译过，可运行。

#include <stdio.h>

#include<math.h>

struct _pid {

int pv /*integer that contains the process value*/

int sp /*integer that contains the set point*/

float integral

float pgain

float igain

float dgain

int deadband

int last_error

}

struct _pid warm,*pid

int process_point, set_point,dead_band

float p_gain, i_gain, d_gain, integral_val,new_integ

/*------------------------------------------------------------------------

pid_init

DESCRIPTION This function initializes the pointers in the _pid structure

to the process variable and the setpoint. *pv and *sp are integer pointers.

------------------------------------------------------------------------*/

void pid_init(struct _pid *warm, int process_point, int set_point)

{

struct _pid *pid

pid = warm

pid->pv = process_point

pid->sp = set_point

}

/*----------------------------------------------------------------------------------

pid_tune

DESCRIPTION Sets the proportional gain (p_gain), integral gain (i_gain),

derivitive gain (d_gain), and the dead band (dead_band) of a pid control structure _pid. ----------------------------------------------------------------------------------------*/

void pid_tune(struct _pid *pid, float p_gain, float i_gain, float d_gain, int dead_band)

{

pid->pgain = p_gain

pid->igain = i_gain

pid->dgain = d_gain

pid->deadband = dead_band

pid->integral= integral_val

pid->last_error=0

}

/*-------------------------------------------------------------------------------

pid_setinteg

DESCRIPTION Set a new value for the integral term of the pid equation.

This is useful for setting the initial output of the pid controller at start up.

--------------------------------------------------------------------------------*/

void pid_setinteg(struct _pid *pid,float new_integ)

{

pid->integral = new_integ

pid->last_error = 0

}

/*----------------------------------------------------------------------------------------

pid_bumpless

DESCRIPTION Bumpless transfer algorithim. When suddenly changing setpoints, or when restarting the PID equation after an extended pause, the derivative of the equation can cause a bump in the controller output.

This function will help smooth out that bump. The process value in *pv should be the updated just before this function is used.

　----------------------------------------------------------------------------------------*/

void pid_bumpless(struct _pid *pid)

{

pid->last_error = (pid->sp)-(pid->pv)

}

/*----------------------------------------------------------------------------------------

pid_calc

DESCRIPTION Performs PID calculations for the _pid structure *a. This function uses the positional form of the pid equation, and incorporates an integral windup prevention algorithim. Rectangular integration is used, so this function must be repeated on a consistent time basis for accurate control. 　RETURN VALUE The new output value for the pid loop.

----------------------------------------------------------------------------------------*/

USAGE #include "control.h"*/

float pid_calc(struct _pid *pid)

{

int err

float pterm, dterm, result, ferror

err = (pid->sp) - (pid->pv)

if (abs(err) >pid->deadband)

{

ferror = (float) err /*do integer to float conversion only once*/

pterm = pid->pgain * ferror

if (pterm >100 || pterm <-100)

{

pid->integral = 0.0

} else {

pid->integral += pid->igain * ferror

if (pid->integral >100.0)

　 　 {

pid->integral = 100.0

} else if (pid->integral <0.0) pid->integral = 0.0

}

dterm = ((float)(err - pid->last_error)) * pid->dgain

result = pterm + pid->integral + dterm

} else result = pid->integral

pid->last_error = err

return (result)

}

void main(void)

{

float display_value

int count=0

pid = &warm

// printf("Enter the values of Process point, Set point, P gain, I gain, D gain \n")

// scanf("%d%d%f%f%f", &process_point, &set_point, &p_gain, &i_gain, &d_gain)

process_point = 30

set_point = 40

p_gain = (float)(5.2)

i_gain = (float)(0.77)

d_gain = (float)(0.18)

dead_band = 2

integral_val =(float)(0.01)

printf("The values of Process point, Set point, P gain, I gain, D gain \n")

printf(" %6d %6d %4f %4f %4f\n", process_point, set_point, p_gain, i_gain, d_gain)

printf("Enter the values of Process point\n")

while(count<=20)

{

scanf("%d",&process_point)

pid_init(&warm, process_point, set_point)

pid_tune(&warm, p_gain,i_gain,d_gain,dead_band)

pid_setinteg(&warm,0.0)//pid_setinteg(&warm,30.0)

//Get input value for process point

pid_bumpless(&warm)

// how to display output

display_value = pid_calc(&warm)

printf("%f\n", display_value)

//printf("\n%f%f%f%f",warm.pv,warm.sp,warm.igain,warm.dgain)

count++

　 }

}