Tutorial 4: Control Systems
Question 3
The control input for a continuous process is derived using a digital controller with a sample period of 0.1 s, and a control algorithm defined by the equations:
u(nT) = e(nT) - e(n-1)T + 0.75u(n-1)T
e(nT) = r(nT) - y(nT)
where r(nT) is the reference input and y(nT) is the sampled output signal. The continuous process is described by the differential equation:
dy/dt + 4y(t) - bu(t) dy/dt
where u(t) is the output from a zero-order hold device.
(1) Provide a block diagram of the closed-loop system, labeling clearly all signals and blocks.
(2) Show that the zero-order hold equivalent of the continuous process is:
0.495 G(z) = 2 - 0.67
(3) Determine the discrete transfer function of the closed-loop system.
(4) Hence, find the transient response of the output, y(nT), when the input is a unit step.