The document discusses the steps to plot the root locus of a control system described by the transfer function G(s)=k(s+2)/(s^2+2s+10). It provides the locations of the poles and zeros, and calculates the number of asymptotes, centroid, and angle of asymptotes. It then determines the angle of departure of the root locus and the breakaway points by setting the derivative of the closed loop characteristic equation equal to zero. No calculation of the intersection points of the root locus with the imaginary axis is needed based on the diagram.
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Root Locus Example
1. By Prof. Hitesh Dholakiya
Root Locus
Example
Control Engineering
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2. Root Locus plot
Asymptotes
Angle of Departure
Break away point
Outlines of Session
Intersection to imaginary axis
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3. Root Locus Plot
? Plot root locus of system given by
? ? =
?(?+?)
??+??+??
? Step 1 : Find position of poles, zeros and loci
? Position of zeros
? Position of poles
?1 = ?2
?1 = ?1 + ?3, ?2 = ?1 ? ?3
Imag
j4
j3
j2
j1
0
-j1
-j2
-j3
-j4
Real
-6 -5 -4 -3 -2 -1
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4. Asymptotes
? Find Number of Asymptotes, Centroid of Asymptotes and Angle of Asymptotes
? Number of Asymptotes
? Centroid of Asymptotes
? Angle of Asymptotes
Imag
j4
j3
j2
j1
0
-j1
-j2
-j3
-j4
Real
-6 -5 -4 -3 -2 -1
Number of Asymptotes = P C Z = 2 C 1 = 1
? ? =
?(? + ?)
?? + ?? + ??
?1 = ?2 ?1 = ?1 + ?3, ?2 = ?1 ? ?3
?? =
σ ???? ????? ?? ????? ? σ ???? ????? ?? ?????
? ? ?
?? =
?1 ? 1 ? (2)
2 ? 1
= 0
? =
(2? + 1)
? ? ?
〜 1800 = 1800
?? = 0
? =180
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5. Angle of Departure
? Angle of Departure
Imag
j4
j3
j2
j1
0
-j1
-j2
-j3
-j4
Real
-6 -5 -4 -3 -2 -1 ?? = 0
? =180
?? = 180 ? ? ????? ?? ???? ? ? ????? ?? ?????
?? = 180 ? ??1 ? ??1 = 180 ? 90 ? 71 = 161
???= 90
???= 71
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6. Break away point
? Characteristics equation
? Find root at
??
??
= ?
Imag
j4
j3
j2
j1
0
-j1
-j2
-j3
-j4
Real
-6 -5 -4 -3 -2 -1 ?? = 0
? =180
???= 90
???= 71
÷ 1 + G S H S = 0
? ? =
?(? + ?)
?? + ?? + ??
?1 = ?2 ?1 = ?1 + ?3, ?2 = ?1 ? ?3
÷ 1 +
?(? + ?)
?? + ?? + ??
= 0
÷ ? = ?
(?2 + 2? + 10)
(? + 2)
÷
??
??
= 0 = ?
? + 2 2? + 2 ? (?2 + 2? + 10)
(? + 2)2
÷ 0 = ?2 + 4? ? 6
÷ ? = 1.16 ÷ ? = ?5.16
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7. Inter section to imaginary axis
? As per Diagram You don¨t need to plot Intersection to imaginary axis
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