ENGR202 2022 Q B2Past paperOld spec ENGR202First25 marks30 min

ENGR202 Summer 2022 Q B2[VALID] official answers

This question concerns the model and control system shown in Figure B2-1.

Figure B2-1: Control system with two negative feedback loops.
Figure B2-1: Control system with two negative feedback loops.
Formulas you may need
  • Steady state gain G(0)G(0); poles from the characteristic equation; quadratic formula s=−a1±a12−4a22s = \dfrac{-a_1 \pm \sqrt{a_1^2 - 4a_2}}{2} (learn this)
  • Negative feedback rule: G11+G1G2\dfrac{G_1}{1 + G_1 G_2}; series rule: G1G2G_1 G_2 (learn this)
  • Pole placement: divide the characteristic equation by the s2s^2 coefficient and match to s2+2ζωns+ωn2s^2 + 2\zeta\omega_n s + \omega_n^2 (learn this)
  • Hurwitz for s3+a1s2+a2s+a3s^3 + a_1 s^2 + a_2 s + a_3: Δ1=a1\Delta_1 = a_1, Δ2=a1a2−a3\Delta_2 = a_1 a_2 - a_3, Δ3=a3Δ2\Delta_3 = a_3\Delta_2, all >0> 0 (learn this)
  1. (a)
    Briefly define and explain what V(s)V(s), X(s)X(s) and U(s)U(s) refer to. Describe one practical example to illustrate your answer.
    [3]
  2. (b)
    Write down the open loop Transfer Function of the control model shown in Figure B2-1. Develop algebraic expressions to determine the steady state gain and the poles of the control model. Use these expressions to calculate numerical values of both the gain and the poles for the case that a1=5.5a_1 = 5.5, a2=7.5a_2 = 7.5 and b1=5b_1 = 5. Determine the stability condition and dominant pole. Finally, for the same numerical example, what is the steady state value of X(s)X(s) for an input magnitude of 5?
    [8]
  3. (c)
    Show that the Closed-Loop Transfer Function associated with Figure B2-1 takes the following form: X(s)=s+b1(1+kV)s2+(a1+kP+kVb1)s+a2+kPb1 V(s)X(s) = \frac{s + b_1}{(1 + k_V)s^2 + (a_1 + k_P + k_V b_1)s + a_2 + k_P b_1}\,V(s)
    [5]
  4. (d)
    For the case that a1=5.5a_1 = 5.5, a2=7.5a_2 = 7.5 and b1=5b_1 = 5, determine the characteristic equation for the Closed-Loop Transfer Function. Design a control system based on Figure B2-1 that achieves a closed-loop damping of 1.0 and a natural frequency of 0.5, i.e. determine suitable values of kPk_P and kIk_I.
    [6]
  5. (e)
    Use the Hurwitz method to determine the stability condition of the following, different, characteristic equation: s3+αs2+βs+γ=0s^3 + \alpha s^2 + \beta s + \gamma = 0.
    [3]