An effect of phase-lag compensation on servo-system performance is that

Lag compensator:

The transfer function of a lag compensator is given by

 \(G\left( s \right) = \frac{{\tau s + 1}}{{\beta \tau s + 1}}\) 

Where, \(\beta = \frac{{{Z_c}}}{{{P_c}}} > 1\)

• Both pole and zero lie in LHS of real plane but PC < ZC i.e. zero is farther away from origin
• Lag Compensation adds a pole at origin (or for low frequencies).
• It helps to reduce the steady-state error of the system.
• An unstable system is a system which has at least one pole at the right side of the s-plane,
• Even if we add a lag compensator to an unstable system, it will remain unstable.

Effects of phase-lag compensator:

• It improves the steady-state response
• It makes the system dynamic response slower. Reduces steady-state error
• Increases the rise time
• Decreases the bandwidth
• Reduces stability margin i.e. the system becomes less stable

Explanation:

Phase lag compensation is an integrator, as it reduces the steady-state error.

We know that

Velocity constant =1/steady state error

The effect of phase-lag compensation on the servo system is that for given relative stability, the velocity constant is increased.