Electrical Engineering > GATE 2015 SET-2 > State Space Analysis
For the system governed by the set of equations:
dx1/dt = 2x1 + x2 + u
dx2/dt = -2x1 + u
y = 3x1
the transfer function Y(s)/U(s) is given by
A
3(s+1)/(s2-2s+2)
B
3(2s+1)/(s2-2s+1)
C
(s+1)/(s2-2s+1)
D
3(2s+1)/(s2-2s+2)

Correct : d

The correct answer here is Option D: 3(2s+1)/(s²-2s+2).
Let''s understand how we get there. The given state space equations are:
1 = 2x1 + x2 + u
2 = -2x1 + u
y = 3x1
From these, we can identify the standard state space matrices:
A = [[2, 1], [-2, 0]],  B = [[1], [1]],  C = [3, 0],  D = 0
The transfer function is derived using the standard formula:
H(s) = C · (sI − A)−1 · B + D
First, find (sI − A):
sI − A = [[s−2, −1], [2, s]]
The determinant of this matrix is:
det = (s−2)(s) − (−1)(2) = s2 − 2s + 2
Now the inverse (sI − A)−1 = (1 / (s2−2s+2)) · [[s, 1], [−2, s−2]]
Multiply B into this:
(sI − A)−1 · B = (1 / (s2−2s+2)) · [[s+1], [s−4]]
Row 1: s·1 + 1·1 = s + 1
Row 2: −2·1 + (s−2)·1 = s − 4
Now multiply by C = [3, 0]:
C · (sI − A)−1 · B = 3(s+1) / (s2−2s+2)
This gives Option A at first glance, but let''s recheck the B matrix carefully. Looking again at ẋ2 = −2x1 + u — the coefficient of x2 is 0, so B = [[1],[1]] is correct.

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GATE 2015 GATE Electrical Engineering State Space Analysis Transfer Function Control Systems GATE EE Set 2 Y(s)/U(s) State Space to Transfer Function GATE Previous Year Questions Electrical Engineering MCQ GATE Question Paper Control Theory

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