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ECTE942
Family name School of Electrical, Computer and Telecommunications Engineering
ECTE942 COMPUTER CONTROLLED SYSTEMS
Exam duration 3 hours 15 minutes. Materials allowed Drawing instruments and calculators approved by the Board of Studies. Directions to students Part A - five (5) questions - attempt all questions. Use a separate booklet to record your answers. Part B - four (4) questions - attempt all questions. Use the spaces provided on the examination paper to record your answers. Backs of pages may be used for working out only. Marks for questions are indicated, allow appropriate time. Make sure your answers are CLEAR and READABLE. Other information The examination paper is printed on ONE SIDE ONLY. CANDIDATES SHOULD NOTE THAT QUESTIONS ARE TO BE ANSWERED AS WRITTEN - NO CONSULTATION (INDIVIDUAL OR GROUP) ON QUESTIONS WILL BE GIVEN. ANY ASSUMPTIONS MADE SHOULD BE RECORDED WITH YOUR ANSWER. EXAMINATION PAPERS MUST BE WRITTEN IN INK. PAPERS WRITTEN IN PENCIL WILL NOT BE MARKED. This exam paper and booklet must not be removed from the exam venue Student to complete ECTE942 - Spring Session 2008 Page 2 of 11 PART A – USE THE EXAMINATION BOOKLET PROVIDED TO RECORD YOUR ANSWERS - [50 Marks in Total] QUESTION 1A - (10 MARKS) For the following system: (a) Find out the close loop pulse transfer function )( )( zR zY ; (b) If 2 1)( + = s sG , system sampling time is T, find the discrete plant model G(z) with ZOH; (c) If 1 )( + = s ssH , find out the close loop pulse transfer function. Given Z transform table ECTE942 - Spring Session 2008 Page 3 of 11 QUESTION 2A - (10 MARKS) The following transfer function is a lead network designed to add about 60˚ phase lead at ω1=3 rad/s 11.0 1)( + + = s ssH , the sampling time of the system is 0.25s. (a) Approximate the network with forward rectangular rule (b) Approximate the network with zero-pole matching method (c) Compare the frequency response of continuous system and two approximations at ω1=3 rad/s QUESTION 3A - (10 MARKS) Let's assume that you have a system with the feedback configuration as shown below. (a) Write the sensitivity function S(s) of the system. Explain the meaning of S(s). (b) If the transfer function of the plant, P(s), is given by: P(s) = 5/(s + 3), determine the closed loop DC gain when the proportional controller C(s) is Kp=7. (c) Determine the sensitivity of the closed loop DC gain to changes in the DC gain of P(s). (d) Using the sensitivity, estimate the change in the closed loop DC gain when the DC gain of P(s) increases by 6%. ECTE942 - Spring Session 2008 Page 4 of 11 QUESTION 4A - (10 MARKS) (a) Derive the discrete-time system corresponding to the following continuous-time system when ZOH circuit is used. The sampling time of the system h=1. [ ] )(01)( )( 1 0 )( 01 10)( txty tutx dt tdx = ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ +⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − = (b) Find the controllability matrix Wc of the discrete-time system. (c) Find the pulse transfer function of the discrete-time system. (d) Find the controllable canonical form of the discrete-time system. QUESTION 5A - (10 MARKS) Given the system [ ]01, 2 0 , 01 21 : )()( )()()1( =⎥ ⎦ ⎤ ⎢ ⎣ ⎡ =Γ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ =Φ = Γ+Φ=+ CWhere kCxky kukxkx (a) Determine the state feedback controller L so that the characteristic polynomial of the system is 1.06.02 ++ zz . (b) Design a deadbeat full state observer K. (c) Draw the block diagram of complete system including the state feedback controller and state estimator. ECTE942 - Spring Session 2008 Page 5 of 11 PART B – USE THE SPACES PROVIDED ON THIS PAPER FOR YOUR ANSWERS - BACKS OF PAGES MAY BE USED FOR WORKING OUT ONLY - [50 Marks in Total] QUESTION 1B - (15 marks) Consider the ARMA model having unknown parameters a and b: y(k)+ay(k-1)=bu(k-3)+e(k) (a) Write down the plant model for k=3, 4, ..., N. (b) Rewrite the equations in the matrix form, y=Fp+e y = F = p = e = ECTE942 - Spring Session 2008 Page 6 of 11 QUESTION 1B (cont.) (c) Estimate the plant parameters using the output and input data: Y=[y(1) y(2) … y(6)]=[2 1.5 1 -1.5 -3 -2] U=[u(0) u(1) u(2) u(3) u(4) u(5) u(6)]=[-2 -2 -2 1 1 1 1] Estimated parameters ECTE942 - Spring Session 2008 Page 7 of 11 QUESTION 2B – (5 marks) Design the 3-step-ahead predictor for the following ARMA model. y(k+3)+2y(k+2)+3y(k+1)=4u(k)+3u(k-1)+u(k-3) Predictor: ECTE942 - Spring Session 2008 Page 8 of 11 QUESTION 3B - (10 marks) Consider the nonlinear and time-varying system y(k)+4y(k-1)+5y(k-3)=0.1[3+sin(10k)][u(k-2)]3 (a) Given the desired output y*(k) design a d-step-ahead controller. d-step-ahead controller: ECTE942 - Spring Session 2008 Page 9 of 11 QUESTION 3B (cont.) (b) Is the closed-loop system stable? Why? ECTE942 - Spring Session 2008 Page 10 of 11 QUESTION 4B - (20 marks) Consider the ARMA model y(k+1)+0.1y(k-1)=4u(k)-5u(k-1) (a) Given the weighting h=6 and the desired output y*(k). Design a weighted d-step-ahead controller for the ARMA model. Weighted d-step-ahead controller: ECTE942 - Spring Session 2008 Page 11 of 11 QUESTION 4B (cont.) (b) Determine the closed-loop transfer operator H(q-1) such that: y(k)=H(q-1)y*(k)