Faculty of Engineering                                        Digital Control
Electrical Power Dept.                                        Transfer function and
  Level four                                                    stability
▪ Transfer function and stability
 1) Consider the following difference equations
     a) y[k] =         y[k-1]+u[k]
     b) y[k] =         0.6y[k-1]+u[k]
     c) y[k] =         0.3y[k-1]+u[k]
     d) y[k] =         u[k-1]
     e) y[k] =         0.707y[k-1]-0.25y[k-2]+u[k-1]
     f) y[k] =         -0.25y[k-2]+u[k-1]
     g) y[k] =         -0 .707y[k-1]-0.25y[k-2]-u[k-1]
       i.  Find the transfer function for each system
      ii.  Find the poles of each system, identify which system is stable
     iii. Assuming zero initial conditions, find the unit pulse response for each
           system analytically.
     iv.   Assuming zero initial conditions, find the unit pulse response for each
           system by successive substitution.
 2) Use the z-transform to determine the output of the difference equation
                   𝑦(𝑘 + 2) − 1.5𝑦(𝑘 + 1) + 0.5𝑦(𝑘) = 𝑢(𝑘 + 1)
    where u is a unit step applied at 𝑘 = 0 and 𝑦(0) = 0.5, 𝑦(−1) = 1
 3) The transfer function of a discrete-time system is
                          0.1 𝑧 + 0.2 𝑧 2 − 0.4𝑧 3 + 0.3 𝑧 4 + 𝑧 5
                   𝐺(𝑧) =
                                            𝑧6
 Find and plot the unit step response of the above system.