申論題

Problem 2 (22%) Consider a control system with the following loop transfer function

whose Nyquist path is shown in Fig. 2.

(b) (6%) Suppose that the Nyquist plot (K＞0) in part (a) is depicted in Fig. 3, and it has an intersection with axis Re(L(s) at K. Using Nyquist criterion and Fig. 3, determine the range of K ＜O such that the closed-loop system is stable. If the system is unstable due to the range of K, find the number of closed-loop pole(s) in the right-half of s-plane.