ST_gram

http://www.rcgroups.com/forums/showthread.php?t=1319827

http://aeroquad.com/showthread.php?5725-Learn-to-fly-quadcopter-with-simulator-and-DX7s

#ifndef PID_H_
#define PID_H_
#include 

//Define parameter
#define epsilon 0.01
#define dt 0.01             //100ms loop time
#define MAX  4                   //For Current Saturation
#define MIN -4
#define Kp  0.1
#define Kd  0.01
#define Ki  0.005

float PIDcal(float setpoint,float actual_position)
{
	static float pre_error = 0;
	static float integral = 0;
	float error;
	float derivative;
	float output;

	//Caculate P,I,D
	error = setpoint - actual_position;

	//In case of error too small then stop intergration
	if(abs(error) > epsilon)
	{
		integral = integral + error*dt;
	}
	derivative = (error - pre_error)/dt;
	output = Kp*error + Ki*integral + Kd*derivative;

	//Saturation Filter
	if(output > MAX)
	{
		output = MAX;
	}
	else if(output < MIN)
	{
		output = MIN;
	}
        //Update error
        pre_error = error;

 return output;
}
#endif /*PID_H_*/

[smartads]       [smartads]
The Matlab simulation of the PID algorithm to control the DC motor

and then embedded PID code:

function output = fcn(error)

%Declare static value
persistent pre_error;
if isempty(pre_error)
    pre_error = 0;
end

persistent integral;
if isempty(integral)
    integral = 0;
end

%Constant Value
epsilon = 0.01;
dt = 0.01;
Kp = 5;
Kd = 3;
Ki = 0.01;

if(abs(error) > epsilon)
    integral = integral + error*dt;
end
derivative = (error - pre_error)/dt;
output = Kp*error  + Ki*integral + Kd*derivative;
pre_error = error;

And result for the simulation

The complete code can be download here:

http://www.mediafire.com/?kati3avzw8b17d9

source from  http://www.embeddedheaven.com/pid-control-algorithm-c-language.htm.

How can get Kp,Ki,Kd??

Ans)

 effective PID parameters are a long story.Manually, you select Kp, first and let's Kd, Ki small.You increase Kp until you get expected setting-time and steady-state error, the more Kp smaller steady-state error and the shorter setting-time.However the more Kp also lead to more overshoot in order to reduce overshoot you increase Kd.Of course, you have to trade-off between Kp and Kd, or setting-time and steady-state versus overshoot.

After all, slightly increase Ki ...

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