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日期:2019-06-07 11:29

School of Electrical, Computer and Telecommunication Engineering

University of Wollongong

Computer Controlled Systems - ELEC442/842 Project

Plant Description

A linearised DC motor system for Control Laboratory is shown in Figure 1, where the motor is in field control. The feedback

from tacho output to the pre-amplifier linearises the motor dynamics and the Servo-amplifier supplies power to the motor. The

input terminal of the linearised motor system is U and the output terminal is V and P. The input u(t) (at point U and in volts) to

the DC motor system comes from a D/A converter installed in a PC; the velocity output v(t) (at point V and in volts) is from the

tacho generator and proportional to velocity of the rotor; the position output p(t) (at point P and in volts) is from a potentiometer

proportional to the position of the rotor.

Figure 1 A DC motor system

The linearised motor system with velocity (tacho voltage) as output can be described using a first order transfer function,

The transfer function with position (potentiometer voltage) as output is


The two transfer functions have different gains and the same time constant. A negative sign is ignored in both transfer functions

for simplicity. Given the speed transfer function

(3)

and the position transfer function

Your task is to design the predictors and controllers for both position and velocity of the DC motor.


Practical 1 - System Modelling and Simulation

1.1 Two discrete time models are to be established for the DC motor using Matlab function c2d. The first has velocity

voltage as its output and the second has position voltage as its output. The sampling period is T=0.07 sec and the

method is zero-order-holder. (You can enter help c2d in Matlab command window for an explanation of Matlab

function c2d. You may also need to define a system using Matlab command sysc=tf(numc,denc))

1.2 Apply a square wave to both discrete time models and simulate the output using Matlab function lsim. Up to 255

samples should be obtained containing 4 to 7 complete periods of the input square wave. (The square wave can be

generated and displayed using the following Matlab command: P=ones(1,25);N=zeros(1,26);PN=[P N];u=[PN PN

PN PN PN]’;plot(u)).

1.3 Apply the same square wave to the continuous time models and compare the outputs with the corresponding outputs

obtained in Question 1.2 by draw them in the same figure. (You can use Matlab Command held on and held off).

Practical 2 - Predictor Design and Simulation

2.1 Design one-step-ahead predictors for both discrete time models

2.2 Predict the plant output using the predictors designed in Question 2.1 and the data obtained in Part 1.2. Compare the

predicted output with the actual output and make comments.

Note: The following is a sample program for simulation of a d-step-ahead predictor

% d=1, G=8 and FBu(k)=9*u(k)+8*u(k-1);

% y and u are output and input from simulation

% yHatP is the prediction of position

yHatP=1:110;d=1;

for k = 2:100,

yHatP(k+d)=8*y(k)+9*u(k)+8*u(k-1); %prediction

end

plot(yHatP(2+d:100+d))

2.3 Generate a normal noise of zero mean and deviation 0.1 using Matlab command randn. Add the noise to the output that

is obtained in question 1.2 in order to study the cases where the output measurement is corrupted by an instrumental

noise. Predict the outputs using the predictors obtained in question 2.1 and the output that is corrupted by the noise.

Compare the results with the noise free case and make comment.

2.4 Change the deviation and predict the outputs. Comment on the effect of noise deviation.

Practical 3 – D-Step-Ahead Controller

3.1 Design d-step-ahead controllers for both discrete time models and discuss stability of the closed-loop sytem.

3.2 Using the d-step-ahead controller to drive the discrete time model outputs to follow a square wave with period of 40T

and amplitude of 10. Plot both plant input and output using Matlab and make comment.

Note: The following is a sample program for simulation of a d-step-ahead controller.

%the plant is y(k)-8y(k-1)=9u(k-1)+8u(k-2)

%the desired output y*(k)=2*sin(0.5*k);

y=1:101;y=y-y;u=y;

for k = 2:100,

u(k)=(-8*u(k-1)+2*sin(0.5*(k+1))-8*y(k))/9; %controller

y(k+1)=8*y(k)+9*u(k)+8*u(k-1); %simulation

end

plot(y);pause;plot(u(1:100))

3.3 Simulate the same controllers using the continuous time plant models. Compare the continuous outputs with the discrete

outputs and make comments.

Practical 4 – Weighted D-Step-Ahead Controller

4.1 Design weighted d-step-ahead controllers for both discrete time models using at least 3 different weightings. Discuss

stability of the closed-loop system and make comment on the effect of the weightings on the stability.

4.2 Redo Question 3.2 and 3.3 using the weighted d-step-ahead controllers and comment on the effect of the weightings on the

stability, overshoot, rise time and tracking accuracy of the closed-loop systems.

Practical 5 – Generalized D-Step-Ahead Controller

5.1 Design a generalised weighted d-step-ahead controller for the discrete time model obtained from plant (3) using

T(q-1)=t0, S(q-1)=s0 and P(q-1)=1+hq-1 where t0=1.3, s0=1.3328 and h=0.1.

5.2 Redo question 3.2 using the controller obtained in the above question.

5.3 comment on the effect of the P, S and T on the performance of the closed loop control system in terms of closed loop poles,

overshoot, rise time and tracking accuracy using at least 2 different values for each of h, t0 and s0.

5.4 Can closed loop poles be placed to any location using a generalized weighted d-step-ahead controller?

Practical 6 – Generalised Predictive Controller

6.1 Design a generalised predictive controller for the discrete time model obtained from plant (3) using

N=1, w1=w0=1 and s1=s0=s

and at least 3 different s values. Discuss stability of the closed-loop system and make comment on the effect of the

weighting, s, on stability.

6.2 Redo question 3.2 using the controller obtained in the above question.

6.3 Compare the controllers you have learnt so far in this part of the subject and make comments on their advantages and

disadvantages.


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