Anna University Coimbatore 2009 B.E Electrical and Electronics Engineering Control system - Question Paper
Wednesday, 16 January 2013 02:45Web
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system.
The frequency domain specifications needed to design a control system are
1. Phase margin 2. Gain margin 3. Resonant peak 4. Bandwidth
3. What is compensation?
The compensation is the design procedure in which the system behaviour is altered to meet the desired specifications by introducing additional device called compensator.
4. What is compensator? elaborate the various kinds of compensator?
The device inserted into the system for the purpose of satisfying the specifications is called compensator. The various kinds of compensators are lag compensator, lead compensator and lag-lead compensator.
5. elaborate the 2 kinds of compensation schemes?
. The 2 kinds of compensation schemes employed in control system are Series compensation and feedback or paralled compensation.
6. What is series compensation?
The series compensation is a design procedure in which a compensator is introduced in series with plant to alter the system behaviour and to give satisfactory performance (i.e., to meet the desired specifications).
Gc (s) = Transfer function of series compensator
G (s) = Open loop transfer function of the plant
H (s) = Feedback path transfer function.
7. What is feedback compensation?
The feedback compensation is a design procedure in which a compensator is introduced in the feedback path so as to meet the desired specifications. It is also called parallel compensation.
Gc (s) = Transfer function of series compensator,G1 (s) G2 (s) = Open loop transfer function of the plant H (s) = Feedback path transfer function.
8. elaborate the factors to be considered for choosing series or shunt/feedback
compensation?
The option ranging from series, shunt or feedback compensation depends on the following: Nature of signals in the systems. Power levels at different points. Components available. Designer's experience. Economic considerations.
9. When lag /lead/lag-lead compensation is employed?
Lag compensation is employed for a stable system for improvement in steady state performance. Lead compensation is employed for stable/unstable system for improvement in transient-state performance. Lag-lead compensation is employed for stable/unstable system for improvement in both steady state and transient state performance.
10. Why compensation is necessary in feedback control system?
In feedback control systems compensation is needed in the subsequent
situations. When the system is absolutely unstable, then compensation is needed to stabilize the system and also to meet the desired performance. When the system is stable, compensation is given to find the desired performance.
11. explain the effect of adding a pole to open loop transfer function of a system.
The addition of a pole to open loop transfer function of a system will decrease the steady state fault. The closer the pole to origin lesser will be the steady-state fault. Thus the steady- state performance of the system is improved. Also the addition of pole will increase the order of the
System, which in turn makes the system less stable than the original
System.
12. explain the effect of adding a zero to open loop transfer function of a
system.
The addition of a zero to open loop transfer function of a system will improve the transient response. The addition of zero
decreases the rise time. If the zero is introduced close to origin then the peak overshoot will be larger. If the zero is introduced far
Away from the origin in the left half of s-plane then the effect of zero on the transient response will be negligible.
13. elaborate the advantages and disadvantages in frequency domain design.
The advantages of frequency domain design are the following:
The effect of disturbances, sensor noise and plant uncertainties are easy to visualize and asses in frequency domain. The experimental info can be used for design purposes.
The disadvantages of frequency response design are that it provide the info on closed loop system's transient response indirectly.
14. What is lag-compensation?
The lag compensation is a design procedure in which a lag compensator is introduced in the system so as to meet the desired specifications.
15. What is a lag compensator? provide an example.
A compensator having the characteristics of lag network is called lag compensator. If a sinusoidal signal is applied to a lag compensator, then in steady state the output will have a phase lag and lead with respect to input.
An electrical lag compensator can be realised by an R-C network. The R-C network shown in the figure is an example of electrical lag compensator
16. elaborate the characteristics of lag compensation? When lag compensation is employed?
The lag compensation improves the steady state performance, decreases the bandwidth and increases the rise time. The increase in rise time outcomes in slower transient response. If the zero in the system does not cancel the pole introduced by the compensator, then lag compensator increases the order of the system by one.
When the provided system is stable and does not satisfy the steady-state performance specifications then lag compensation can be employed so that the system is redesigned to satisfy the steady-state requirements.
17. What is lead compensation?
The lead compensation is a design procedure in which a lead compensator is introduced in the system so as to meet the desired specifications.
18. What is lead compensator? provide an example.
A compensator having the characteristic of a lead network is called a lead compensator. If a sinusoidal signal is applied to a lead compensator, then in steady state the output will have a phase lead with respect to input. An electrical lead compensator can be realised by a RC network. The R-C network shown in the figure is an example of electrical lead compensator.
19. elaborate the characteristics of lead compensation? When lead compensation is employed?
The lead compensation increases the bandwidth and improves the speed of response. It also decreases the peak overshoot. If the pole introduced by the compensator is not cancelled by the zero in the system, then lead compensation increases the order of the system by one. When the provided system is stable/ unstable and requires improvement in transient state response then lead
compensation is employed.
16 Marks
1. Write the transfer function of a typical lag-lead compensaton
2. Write the procedure to design a lag-lead compensator
3. A unity feed back system has an open loop transfer function
G(s) = k /(s(s+1)). Design a suitable phase lead compensator to achieve the subsequent specifications: kV =0 and phase, margin> 45? with usual notations.
4. Write the transfer function of a typical lead compensator
5. Write the procedure to design a lead compensator
6. A unity feed back system has an open loop transfer function
G(s) = k /(s(s+1)). Design a suitable phase lag compensator to achieve the subsequent specifications: kV =8 and phase margin= 40? with usual notations.
7.Write the transfer function of a typical lag compensator
8. Write the procedure to design a lag compensator
9.Design a cascade phase compensator for the system whose
GH(s)=10 /s (1+s) to have a phase margin of 45 degrees using bode plot.
| Earning: Approval pending. |
