Lead compensator vs lag compensator?

A lead compensator can increase the stability or speed of reponse of a system; a lag compensator can reduce (but not eliminate) the steady-state error. Depending on the effect desired, one or more lead and lag compensators may be used in various combinations.

1. What is the difference between lead and lag compensator?
2. Why use lead-lag compensator?
3. Is Pi a lead or lag compensator?
4. What is the disadvantage of the lag compensator?

What is the difference between lead and lag compensator?

The lead compensator provides phase lead at high frequencies. This shifts the root locus to the left, which enhances the responsiveness and stability of the system. The lag compensator provides phase lag at low frequencies which reduces the steady state error.

Why use lead-lag compensator?

Lead-lag compensators are used to improve the gain and phase margin for stability of closed-loop system, and to boost bearing stiffness and damping in specific frequency ranges.

Is Pi a lead or lag compensator?

In the lead-lag compensator, the lead part is used to improve PM (hence the transient response), while the lag (or PI) part is used to improve steady state performance (i.e., by increasing the dc-gain).

What is the disadvantage of the lag compensator?

Disadvantages of Lag Compensator

In lag compensator, the attenuation offered by it shifts the gain crossover frequency to a lower point, thereby decreasing the bandwidth. Though the system response is longer due to decreased bandwidth; however, the response is quite slow.