Chatter Elimination in EMTP Simulations using State-Space Models of Companion Circuits

The occurrence of spurious, negligibly damped numerical oscillations (chatter) in the outputs of EMTP simulation programs is well known. In this paper, a novel insight into chatter occurrence is given by showing that chatter is one of the dynamic modes of the Companion Circuit. It is shown that the state-space modeling of Companion Circuits is not laborious since the need for checking the independence of state variables does not arise. The expression for computing the state matrix from netlist information is given. The eigenvalues of the Companion Circuit are related with those of the actual circuit and is shown that the eigenvalues exactly or approximately equal to -1 are related to the chatter mode. A novel method to suppress chatter by using the left and right eigenvectors corresponding to chatter mode is proposed. An alternative way to compute the eigenvectors of chatter mode is proposed based on observing the relations between these eigenvectors and circuit topological information such as cutsets involving only inductors and the switch being turned off in various circuit examples. The results from the proposed chatter elimination method are compared with the simulation outputs from PSCAD/EMTDC.