The Performance of P Controller : The error signal is positive, the torque is positive and rising rapidly. The large overshoot and oscillations in the output because lack of damping. : The error signal is negative, the torque is negative and slow down causes the direction of the output to reverse and undershoot. : The torque is again positive, thus tending to reduce the undershoot, the error amplitude is reduced with each oscillations.
The contributing factors to the high overshoot The positive correcting torque in the interval is too large ( ) Decrease the amount of positive torque The retarding torque in the interval is inadequate ( ) Increase the retarding torque
The Effect of PD Controller : is negative; this will reduce the original torque due to alone. : both and is negative; the negative retarding torque will be greater than that with only P controller. : and have opposite signs. Thus the negative torque that originally contributes to the undershoot is reduced also.
HW5 : The Effect of PI Controller Adds a zero at to the forward-path T.F. Adds a pole at to the forward-path T.F. This means that the steady-state error of the original system is improved by one order. a=2,b=8,k=1
Program of PID Controller clear; x1=0;x2=0;dt=0.01;r=1;step=2000; kp=1;kd=6;ki=0.1;pe=r-x1;ie=(r-x1)*dt; for k=1:step t(k)=k*dt; e=r-x1; de=(e-pe)/dt; ie=ie+e*dt; u=kp*e+kd*de+ki*ie; x1=x2*dt+x1; x2=(u-2*x2-8*x1)*dt+x2; pos(k)=x1;vel(k)=x2;pe=e; end