Detailed Parametric Modeling of AC–DC Converters for EMT Simulators

Abstract

Detailed switching models of ac–dc converters are available in many offline and real-time electromagnetic transient (EMT) simulation programs. However, such discrete models typically require small simulation time steps for accurately handling the switching events without interpolation. This paper proposes a new parametric modeling approach for line-commutated and 2-level voltage-source ac–dc converters. The proposed methodology is based on parametric functions that relate ac and dc variables in the instantaneous sense, which allows the reconstruction of the waveforms of voltages and currents (with the same level of details as the switching models of converters) without topological changes in the converter circuit. Thus, it can operate at larger time steps without requiring interpolation, thereby enhancing simulation efficiency. The computational advantages of the proposed models over the conventional switching models are demonstrated in offline PSCAD and real-time RTDS NovaCor simulators in terms of maximum possible time step size and accuracy. It is shown that the proposed models can accurately run with much larger time steps (up to ∼200 μs for LCRs, and up to ∼50 μs for VSCs) compared to detailed switching models, which are limited to relatively small time steps of ∼10 μs.

Keywords

• Ac–dc converter
• interfacing
• line-commutated
• modeling
• nodal analysis
• real-time