Multi-timescale simulator of nonlinear electrical elements by interfacing shifted equivalent phasors and electromagnetic transient simulation

Abstract

This paper proposes a multi-timescale transient branch companion model for electrical elements with strong nonlinearity, which is suitable for electromagnetic transient simulation for a wide range of time-scales. A shifted equivalent phasor (SEP) method for signals with wide frequency range is adopted combined with envelope signals and equivalent phasor-shift operator, and a saturable SEP based transformer model is established. A method of piecewise linearization based on Newton-Raphson is used to simulate excitation current under different simulation time step sizes in order to illustrate the overshoot phenomenon of piecewise linearization under large step sizes. Reducing the step size can effectively suppress the overshoot, but simulation efficiency will be sacrificed. This problem can be avoided in SEP model even if large time step is adopted and integrated simulation of both instantaneous and envelope (with larger timescale) waveforms can be efficiently tracked within one simulation run based on the determination of two parameters setting: shifting equivalent phasor and time step size. Finally, the transformer model and voltage source converter (VSC) are established and validated in MATLAB and PSCAD to prove its correctness and efficiency.