Anna University Coimbatore 2008 B.E Electrical and Electronics Engineering Control system unit 1 - Question Paper

17.What is Nichols chart?
The chart consisting if M & N loci in the log magnitude versus phase
diagram is called Nichols chart.

18.What are 2 contours of Nichols chart?
Nichols chart of M and N contours, superimposed on ordinary graph. The M contours are the magnitude of closed loop system in decibels and the N contours are the phase angle locus of closed loop system.

19.How is the Resonant Peak(Mr), resonant frequency(Wr ) , and band width determined from Nichols chart?
i) The resonant peak is provided by the value of omega.contour which is tangent to G(j omega ) locus.
ii) The resonant frequency is provided by the frequency of G(j omega ) at the tangent point.
iii) The bandwidth is provided by frequency corresponding to the intersection point of G(j omega ) and –3dB M-contour.

20What are the advantages of Nichols chart?
The advantages are:
i) It is used to obtain the closed loop frequency response from open loop frequency response.
ii) Frequency domain specifications can be determined from Nichols chart.
iii) The gain of the system can be adjusted to satisfy the provided specification.
21.What are the 2 kinds of compensation
i. Cascade or series compensation
ii. Feedback compensation or parallel compensation
22.What are the 3 kinds of compensator s
i. Lag compensator
ii. Lead compensator
iii. Lag-Lead compensator
23.What are the uses of lead compensator
• speeds up the transient response
• increases the margin of stability of a system
• increases the system fault constant to a limited extent.
24.What is the use of lag compensator
*Improve the steady state behavior of a system, while nearly preserving its transient response.

25.When is lag lead compensator is needed
The lag lead compensator is needed when both the transient and steady state response of a system has to be improved
26.What is a compensator
A device inserted into the system for the purpose of satisfying the specifications is called as a compensator.
26.What is nyquist contour
The contour that encloses entire right half of S plane is called nyquist contour.



27.State Nyquist stability criterion.
If the Nyquist plot of the open loop transfer function G(s) corresponding to the nyquist control in the S-plane encircles the critical point –1+j0 in the counter clockwise direction as many times as the number of right half S-plane poles of G(s),the closed loop system is stable.
28.Define Relative stability

Earning:   Approval pending.