In any power system network, All parameters (Voltages, Current, Real power, Reactive power & Machines oscillation damping) stability improvement is very important. If system parameters could not be stable then some unexpected loss will occur, even machines may loss it’s synchronism. In this book, two types of FACTS devices(SVC & SSSC) has been considered for stability improvement & some external controllers(PI, PD, POD, PID, Generic controllers) has been designed to achieve the better performance of those FACTS devices. Controller parameters has been selected by using different methods i.e. Trail & Error methods ,Ziegler-Nichols close loop tuning method & Proposed Triple Integral Differential(TID) close loop tuning methods. Those FACTS devices with controllers has been applied in the power system network & After simulation it is seen that, Every parameters(V,P,Q,I,d?) becomes stable . Only small ratings of FACTS devices can regain stability in faster way then without controllers. At last, the performance of FACTS devices with TID tuning methods are highly efficient & suitable among them.