Flexible numerical integration for efficient representation of switching in real time

In real time digital simulation of electromagnetic transients for equipment testing, solution output is provided at equidistantly spaced time points in order to synchronize the data exchange with external equipment. Switching events, which can occur in between these time points of solution output, are pinpointed by backward interpolation. To recuperate the time interval lost through interpolation, the simulation must be resynchronized with the real time clock. For this purpose, the use of a flexible time step size is desirable. However, in electromagnetic transients simulators based on nodal analysis techniques, time step size changes have so far involved changes of the nodal admittance matrix and thus imposed a large computational burden. This is avoided through the method flexible integration for readjustment in simulation of transients (FIRST), presented in this paper. Through this method, the characteristics of numerical integration are modulated such that time step size changes are achieved in a computationally very efficient manner and without modifying the nodal admittance matrix.