Application of a Varying Elements Tracing Method to Partial Refactorization in an Electromagnetic Transient Analysis Program

Abstract

Faster calculation methods are desired for electromagnetic transient (EMT) simulation programs, since circuits simulated are becoming increasingly larger and more complex. If there are time-varying and non-linear elements in the circuit to be solved, the solution process requires repeated factorization of the coefficient matrix of the circuit equations. The repeated factorization, which is often called refactorization, significantly increases the computation time. Up to now, the bottom right arranging (BRA) method has been applied for refactorization in EMT simulation programs in order to reduce the computation load. In this paper, the author proposes the use of the varying elements tracing (VET) method, which is one of the refactorization methods proposed for power flow calculations, for an offline EMT simulation program. Using some test circuits, the computation time by the BRA method and that by the VET method are examined, and the following facts are found. In most test circuits, both methods greatly improve refactorization speed, but in some test circuits, the BRA method shows degraded refactorization speed due to increased fill-ins. As for the entire EMT simulation time, the VET method improves the refactorization speed by a factor of 1.6 times at most. On the other hand, the BRA method improves the refactorization speed by a factor of 1.5 times in the best case but degrades it in some test circuits.