Give selection procedure of compensation.

1) In general there are two situation in which compensation is required.

2) In 1st case, the system is absolutely unstable & the compensation is required to stabilize, if as well as to achieve a specified performance.

3) In 2nd case the system is stable, but the compensation is required to obtain the desired performance.

4) The system which are type 2 or higher are usually absolutely unstable, for these type of system clearly load compensator increase the margin of stability.

5) In type 0, type 1 system stable operation is always possible, if the gain if sufficiently reduced. In Such cases any of the 3 compensator lead, lag and Lead lag may be used to obtained the desired performance.

Compare lead and lag compensator

 Lead compensator   

1) Introduce lead phase shift in the system

2) Improve transient response

3) Decrease rise time 

4) Decrease settling time 

5) Increase Bandwidth

6) Faster response

7) less overshoot

8) Increasing damping

Lag compensator 

1) Introduce lag phase shift in the system

2) Improve steady state response

3) Increase rise time. 

4) Increase settling time.

5) Decrease Bandwidth 

6) Slow response 

7) Increase overshoot.

8) Decrease damping