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

Transient phenomena of power systems and their control system are simulated using EMTP (Electromagnetic Transients Program) and TACS (Transient Analysis of Control Systems) software respectively. The internal variables are transmitted between the two routines, and numerical solutions are performed separately at each time step. This implies time delays exist in the 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 software 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.