ELEC 9732 Final Exam
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ELEC 9732 Final Exam
Gain Scheduling |
In magnetic levitation a ball (of mass m) of magnetic material is suspended by an electro-magnet (EM).
Newton’s law gives (with y the distance from the ground to the centre of gravity of the ball)
L0 I2 β
=
2(1 + yβ)2
where I is the current applied to the EM and k > 0 is a viscosity coefficient. Also β > 0 is a scaling constant. The inductance has been assumed to vary inversely with y . We also assume for simplicity that the EM is driven directly by a current source.
(i) Express the equations in state space form.
(ii) Find the operating point for holding the ball at a fixed target height y = y0 .
(iii) Discuss the stability of the system at the oper- ating point.
(iv) Using linearization develop a linear control law valid near the operating point.
(v) Treating the target height as the scheduling vari- able extend the design to a gain-scheduled de- sign. Comment on any limitations of the gain- scheduled control law.
Sliding Mode Control |
A pendulum with moving suspension point is de- cribed by,
mL + mgsin(φ) + kLφ˙ = T/L + ma(t)cos(φ).
where,
a(t) = of the suspension point;
T = torque applied at the suspension point; m = pendulum mass & L = pendulum length; k = friction coefficient
φ(t) = angle from the vertical.
The aim is to stabilize the pendulum at φ = 0.
Assume g = 9.81 and .9 < L < 1.1;
.5 < m < 1.5 and 0 < k < .2 and la(t)l < 1.
(i) Design a sliding mode stabilizing controller that avoids chattering.
(ii) Show how the control design parameters can be chosen to ensure lφl < .01 & lφ˙ l < .01.
Stability |
2a Consider a linear time-invariant system with in-
put u(t) and output y(t) and transfer function G(s). Suppose
Re[G(jω)] 2 2∈ > 0 and lG(jω)l < c
where c is a constant.
Show that the system is strictly passive with
T T T
0 0 c2 0
2b Consider the nonlinear system
x˙1 = x2 _ x1(3) + r
x˙2 = _x2 + a(x1(3) _ r)
where 0 < a < 1 and r(t) is a system input. Take the initial conditions to be x1 (0) = 0 = x2 (0). Using the result of 2a,
(i) Show that the system is energy input en- ergy output stable.
(ii) Then show that
supt lx1 (t)l < o and supt lx2 (t)l < o
2022-11-26