Numerically Efficient Model of Voltage-Source Converters for Power Systems Transient Studies

Voltage source converters (VSCs) enable the vast integration of renewable energy resources in modern power systems. Planning and analysis of VSC-based power systems require numerically efficient and accurate models of VSCs. The traditional discrete switching models of VSCs are computationally burdensome; therefore, the average-value models (AVMs) are indispensable for system-level studies. Conventionally, the AVMs of VSCs are interfaced with external subsystems using dependent voltage and current sources in nodal analysis-based programs. This classical type of indirect interfacing of AVM (IDI-AVM) requires a one-time step delay inherently which can cause numerical inaccuracy and/or instability. Recently, a directly-interfaced AVM (DI-AVM) was proposed for VSCs in which the interfacing delay is avoided. This was achieved by formulating the new AVM as a conductance matrix that merges with the overall network nodal equations so that it can be solved with the external subsystems simultaneously and without inducing latency. In this paper, the computational performance of the DI-AVM is investigated against the IDI-AVM for a large-scale VSC-based wind generation system. It is verified that the DI-AVM outperforms the IDI-AVM of VSCs in terms of numerical accuracy as well as efficiency by enabling large simulation time steps.