r
+e
Gc(s)
G(s)
y
Figure 1: Feedback Control System
Problem 1. (10 points) Consider the feedback control system in Figure 1, where
20
G(s) = \frac{20}{(s+1)(s+20)}
Using lead-lag design in the frequency domain, determine the parameters K > 0, N ? N,
a_i > 1, \tau_i > 0, i = 1,2, of the cascade compensator
G_c(s) = \frac{K}{s} \frac{1 + \tau_1 s}{1 + \alpha_1 \tau_1 s} \frac{1 + \alpha_2 \tau_2 s}{1 + \tau_2 s}
such that the following specifications are satisfied:
• The closed-loop system has a 10% steady-state error with respect to a ramp input.
• The percent overshoot to a step reference input is less or equal than 10%.
• The crossover frequency of F(j?) = G_c(j?)G(j?) satisfies ?_c ? 0.5 rad/s.
• The gain margin satisfies G_m ? 25 dB.