Discrete PI Algorithm as a MATLAB S-file

gistfile1.matlab

function [sys,x0,str,ts]=pialg2(t,x,u,flag,k,z1,dt,vmin,vmax) 
%discrete PI algorithm 
%v(nh)=k*u(nh)-k*z1*u((n-1)h)+v((n-1)h) 
% dt  sampling time, the same as h. 
if abs(flag)==2 
 sys(1)=k*(1-z1)*u+x(1); 
elseif flag==3 
 v=k*u+x(1); 
 if v>vmax 
  v=vmax; 
 elseif v<vmin 
  v=vmin; 
 else v=v; 
 end 
 sys(1)=v; %output signal 
elseif flag==4 
 sys(1)=t+dt; 
 t=sys(1); 
elseif flag==0 
 sys(1)=0; %number of continuous states 
 sys(2)=1; %number of discrete states 
 sys(3)=1; %number of outputs 
 sys(4)=1; %number of inputs 
 sys(5)=0; 
 sys(6)=0; 
 sys(7)=1; 
 x0(1)=0; 
 ts=[dt,0]; 2
else 
 sys=[]; 
end

gistfile2.matlab

% Found this on a chinese forum for PID control
%

s-function source code is as follows: 
function [sys, x0, str, ts] = pidcon (t, x, u, flag, Kp, Ti, Td, T, E, uk) 
global umax Ki Kd uk_1 ek_1 ek_2 B 
switch flag 
case 0,% initialize some 
sizes = simsizes; 
sizes.NumContStates = 0; sizes.NumDiscStates = 0; 
sizes.NumOutputs = 1; sizes.NumInputs = 1; 
sizes.DirFeedthrough = 1; sizes.NumSampleTimes = 1; 
sys = simsizes (sizes); str = []; 
ts = [T 0]; 
umax = 50; uk_1 = 0; ek_1 = 0; ek_2 = 0; Ki = Kp * T / Ti; Kd = Kp * Td / T% initialize the controller parameters 
case 3,% controller output calculation 
ek = u;% for the error 
if abs (ek) <E 
B = 1; 
else 
B = 0; 
end 
uk = uk_1 + Kp * (ek-ek_1) + B * Ki * ek + Kd * (ek-2 * ek_1 + ek_2);% PID control law 
if uk> umax 
uk = umax; 
end 
if uk <-umax 
uk =- umax; 
end 
uk_1 = uk; ek_2 = ek_1; ek_1 = ek; 
sys = [uk]; 
uk = uk_1 + Kp * (ek-ek_1) + B * Ki * ek + Kd * (ek-2 * ek_1 + ek_2) 
case {1,2,4,9}, 
sys = []; 
otherwise 
error (['Unhandled flag', num2str (flag)]); 
end

gistfile3.matlab

% copied the first file again

function [sys,x0,str,ts]=pialg2(t,x,u,flag,k,z1,dt,vmin,vmax)
%discrete PI algorithm
%v(nh)=k*u(nh)-k*z1*u((n-1)h)+v((n-1)h)
% dt  sampling time, the same as h.
if abs(flag)==2
  sys(1)=k*(1-z1)*u+x(1);
elseif flag==3
	v=k*u+x(1);
	if v>vmax
		v=vmax;
	elseif v<vmin
		v=vmin;
	else v=v;
	end
	sys(1)=v;	%output signal
elseif flag==4
	sys(1)=t+dt;
	t=sys(1);
elseif flag==0
	sys(1)=0; %number of continuous states
	sys(2)=1; %number of discrete states
	sys(3)=1; %number of outputs
	sys(4)=1; %number of inputs
	sys(5)=0;
	sys(6)=0;
	sys(7)=1;
	x(1)=0;
	ts=[dt,0];
else
	sys=[];
end