Suppression of numerical oscillation caused by the EMTP-TACS interface using filter interposition

Transient pheriomena of power system and the control system are simulated in EMTP (Electromagnetic Transients Program) and TACS (Transient Analysis of Control Systems) respectively. The internal variables are transmitted between two routines, and numerical solutions are done separately at each time step. This implies time delays exist in EMTP-TACS interface. These may cause undesirable effects such as numerical instabilities and incorrect results. In this paper, both the power system part inside the EMTP and the control system part inside the TACS are regarded as a feedback system from the viewpoint of system stability, the characteristics of these interface delays are clarified, and a method to suppress numerical oscillations based upon filtering is proposed. This method is simple and imposes no restrictions with respect to practical use.