Both SVC (Static Var Compensator) and STATCOM (Static Synchronous Compensator) are important equipment of reactive compensation, which are compared in voltage supporting, improving the transient stability and transmission limit, and damping low frequency oscillation. Simulation results are presented as high capacity static var system for SVC or STATCOM is placed on transmission path of power system. Firstly, single SVC and STATCOM are limited in voltage supporting after fault occurrence, but STATCOM is little better than SVC. Secondly, STATCOM is much better than SVC in improving the transient stability and transmission limit. Thirdly, on the damping low frequency oscillation, STATCOM is much better than SVC as SVC and STATCOM have the same capacity, and performs similarly with SVC as the two have the same controllable capacity. Lastly, the results also indicate that dynamical response speed effects the control result little though STATCOM responses much faster than SVC.
Based on the argument principle, a method is proposed to derive delay-dependent stability criteria without any conservatism for LTI (linear time invariant) systems with multiple time delays. Because the characteristic polynomial of a LTI system with multiple time delays is analytic in the whole complex plane, we use the argument principle to judge whether the characteristic equation has roots in the right-half complex plane. We construct a new function based on the characteristic polynomial so as that the criteria take a straightforward form, and can be used conveniently. The criteria can be considered as a generalized Nyquist criterion. The criteria are sufficient and necessary for the stability of the system. The method involves no symbol calculation so as that can deal easily with the systems of which the orders and time delays are more than 3. The example case study shows that the criteria can judge whether a LTI system is stable exactly, for any given time delays.
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