lag compensation

Lag Compensation :”using Operational amplifier”

    

ü  Lag Compensation Techniques based on the root locus approach .

ü  Consider the problem of finding a suitable compensation network for the case where the system exhibits satisfactory transient-response characteristics but un satisfactory steady state characteristics .

ü  Compensation in this case essentially consists of increasing the open-loop gain without appreciably changing the transient response characteristics .

ü  That means that the root locus in the neighborhood of the dominant closed –loop poles shouldn’t be changed appreciably , but the open loop gain should by increased as much as needed .

ü  This can be accomplished if a lag compensator is put in cascade with the given feedforward transfer functions .

ü  To avoid an appreciable change in the root locus , the angle contribution of the lag network should be limited to a small amount .     

Applications :

Ø  lag compensators influence disciplines as varied as robotics, satellite control, automobile diagnostics, laser frequency stabilization, and many more. They are an important building block in analog control systems, and can also be used in digital control.

Design Procedures for lag compensation by the root-locus method :

1-      Draw the root locus plot for the uncompensated system whose open-loop transfer function G_c(s)

2-      Assume transfer function is

3-      Evaluate the static error constant in the problem.

4-      Determine the amount of increase in the static error constant .

5-      Determine the pole and zero of the lag compensator that produce the necessary increase in the particular static error .

6-      Draw new root-locus plot for compensated system.

7-      Adjust gain K of the compensator.