Numerically Enhanced Interfacings for Average-Value Models of Voltage-Source Converters in Nodal-Based EMT Simulators

Efficient simulations of converter-dominated power systems and microgrids significantly rely on average-value models (AVMs) of the converters. The conventional AVMs of voltage-source converters (VSCs) typically require a time-step delay for interfacing with the external circuits in non-iterative nodal-based electromagnetic transient (EMT) programs. This time-step relaxation may lead to numerical inaccuracy and/or instability for simulations with large time-step sizes. This paper presents several alternative formulations and interfacing techniques for AVMs of VSCs, which eliminate undesirable time-step delays and result in robust and reliable interfaces that allow simulations at large time steps without significant compromise in numerical accuracy. This is achieved by formulating the VSCs as conductance matrices (and history terms), which are computed simultaneously with the solution of the external network. The advantages of the proposed techniques over the conventional methods are demonstrated in simulations of a VSC-dominated power system using the EMT program PSCAD.