A Fast Time-Step Selection Method for Explicit Solver-Based Simulation of High Frequency Low Loss Circuit and Its Application on EMI Filter

Electromagnetic interference (EMI) modeling and prediction are essential for the design of most power electronics apparatuses. This article aims at finding a fast method to select time step for explicit solver-based simulation of high frequency low loss (HFLL) circuits like EMI filter. The state-space model of HFLL circuit is constructed and its eigenvalues are proved to be very close to the imaginary axis. Both the nondegenerate and degenerate circuit cases are discussed. During the analysis, a circuit lemma is summarized on how to transform degenerate circuit into nondegenerate circuit and the corresponding inversion of its coefficient matrix is derived based on Sherman–Morrison's formula. Then the Laguerre–Samuelson's inequality is employed to find the upper bound of HFLL circuit's eigenvalues. This process only requires two matrix multiplications and traces of the matrix operation results, thus keeping the computational complexity retaining in $O(N^2)$. A typical EMI filter is constructed and its equivalent circuit including the parasitic effects is extracted from ANSYS. This filter is simulated in application between a dc/ac converter and the grid using the fourth-order Runge–Kutta (RK4) solver with a time step selected by the proposed method. Numerical test shows that the spectrum results are very close to those obtained by experiment while being much more efficient than traditional methods, which demonstrates that this time-step selection method could benefit the analysis and time-domain simulation of HFLL circuits.