增量pid的阶跃跟踪程序

				%Increment PID Controller
				clear all;
				close all;
				
				ts=0.001;
				sys=tf(400,[1,50,0]);
				dsys=c2d(sys,ts,'z');
				[num,den]=tfdata(dsys,'v');
				
				u_1=0.0;u_2=0.0;u_3=0.0;
				y_1=0;y_2=0;y_3=0;
				
				x=[0,0,0]';
				
				error_1=0;
				error_2=0;
				for k=1:1:1000
				   time(k)=k*ts;
				   
				   rin(k)=1.0;
				   kp=8;
				   ki=0.10;
				   kd=10;
				   
				   du(k)=kp*x(1)+kd*x(2)+ki*x(3); 
				   u(k)=u_1+du(k);
				
				   if u(k)>=10
				      u(k)=10;
				   end
				   if u(k)				      u(k)=-10;
				   end   
				   yout(k)=-den(2)*y_1-den(3)*y_2+num(2)*u_1+num(3)*u_2;
				   
				   error=rin(k)-yout(k);
				   u_3=u_2;u_2=u_1;u_1=u(k);
				   y_3=y_2;y_2=y_1;y_1=yout(k);
				   
				   x(1)=error-error_1;             %Calculating P
				   x(2)=error-2*error_1+error_2;   %Calculating D
				   x(3)=error;                     %Calculating I
				   
				   error_2=error_1;
				   error_1=error;
				end
				plot(time,rin,'b',time,yout,'r');
				xlabel('time(s)');ylabel('rin,yout');