Dynamic modeling of high power static switching circuits in the dq-frame

With the proliferation of static switching circuits in power systems, there is a need to understand not only their steady-state behaviour but their dynamic interaction with the network as well. Analysis is difficult due to the nonlinear nature of switching processes associated with such devices. Linear, time-invariant (LTI) dynamic models are needed for standard analytical tools such as eigenanalysis for the study of inter-area as well as higher frequency modes of the system. To this end, LTI small-signal dynamic models are developed for high power static switching circuits in a synchronous rotating dq-reference frame. Two conventional devices are chosen for study: a thyristor controlled series capacitor (TCSC) and a HVDC power converter. The proposed models are shown to represent the dynamic response of the static switching circuits to nominal changes in operating point. In particular, the damping characterizing the dynamic behaviour of the TCSC is shown to vary significantly with operating point. This accounts for the observed responses arising from field tests and simulations but not accounted for by the quasi-static model. On the other hand, the damping characterizing the dynamic behaviour of the HVDC converter is shown to vary little with operating point. The linearized models are validated by digital time-domain simulation of the nonlinear static switching circuits.