a) What is the Nyquist sampling theorem in discrete time systems?
In practice, how should the sampling frequency be chosen in discrete time control systems?
b) Given the discrete-time system:
y(k + 1) - y(k) = u(k + 1)
find the system transfer function and its response to a sampled unit step.
c) A linear system is controlled using a discrete time controller shown in Figure 1.
Figure 1: Block diagrarn of a discrete time control system
i) Write the equation of the discrete time open loop transfer function.
ii) Write the characteristic equation for this system.
iii) For a sampling time period T = 1sec: calculate the critical gain of this system The root locus leaves the unit circle at z = -1.