Lead frequency compensation is a technique used to increase

Lead compensator:

Transfer function:

If it is in the form of , then a > 1

If it is in the form of , then a < b

Maximum phase lead frequency: 

Maximum phase lead: 

ϕm is positive

Pole zero plot:

The zero is nearer to the origin.

Filter: It is a high pass filter (HPF)

Effect on the system:

• Rise time and settling time decreases and Bandwidth increases
• The transient response becomes faster
• The steady-state response is not affected
• Improves the stability
• The velocity constant is usually increased
• Helps to increase the system error constant though to a limited extent
• The slope of the magnitude curve is reduced at the gain crossover frequency, as a result, relative stability improves
• The margin of stability of a system (phase margin) increased

Lag compensator:

Transfer function:

If it is in the form of , then a < 1

If it is in the form of , then a > b

Maximum phase lag frequency: 

Maximum phase lag: 

ϕm is negative

Pole zero plot:

The pole is nearer to the origin.

Filter: It is a low pass filter (LPF)

Effect on the system:

• Rise time and settling time increases and Bandwidth decreases
• The transient response becomes slower
• The steady-state response is improved
• Stability decreases