Question

The polar plot of an open loop stable system is shown below. The closed loop system is .

• A. always stable
• B. marginally stable
• C. unstable with one pole on the RHS s-plane
• D. unstable with two poles on the RHS s-plane

Answer 1

The correct option is D unstable with two poles on the RHS s-plane


Two clockwise encirclement of 1+j0.
$N=-2$
Open-loop system is stable$\Rightarrow P=0$
$N=P-Z$
$-2=0-Z$
Z=Number of closed loop poles in RHS of 8-planes. Hence the system is unstable.