Taleb Vahabzadeh's research while affiliated with University of British Columbia and other places

Aggregated modeling of converter-interfaced resources (CIRs) can decrease the computational complexity in time-domain simulations of electric grids with high penetration of renewable sources. This paper presents admittance-based aggregated modeling (ABAM) for grid-following CIRs. The aggregation is carried out by representing the CIRs' current controllers and output filters using transfer functions and aggregating them as admittances and sources. For improved aggregation accuracy, the CIRs are grouped in terms of their ratings, synchronization system parameters, and collector system parameters. The numerical advancements of the proposed ABAM are shown in an example renewable energy system consisting of multiple grid-following CIRs. It is verified that the ABAM has low sensitivity to the parameters and excellent accuracy in capturing the dynamics of heterogeneous CIRs compared to the conventional preserved-structure aggregated model with weighted-mean parameters. The proposed ABAM also permits the use of large time-step sizes with acceptable numerical accuracy in (offline) MATLAB/Simulink and (real-time) OPAL-RT simulators.

Efficient and accurate simulation tools are crucial for studying the dynamics and stability of modern power systems with high penetration of voltage-source converters (VSCs). This paper proposes an admittance-based electromagnetic transient program (ABM-EMTP) approach for analyzing large-scale VSC-based energy conversion systems. Compared to the traditional EMTP approach with a detailed representation of all switches or the use of average-value models for the VSCs, the proposed approach applies impedance-based modeling to the VSC-based resources, which reduces the effective network to be simulated and the size of the overall nodal equation. An additional benefit is that the constructed admittances may be used for the small-signal stability analysis conducted within the EMTP environment. The benefits of the proposed approach over the conventional method that uses AVMs of VSCs are demonstrated on a VSC-based energy conversion system in the offline (PSCAD) and real-time (RTDS) transient simulations. It is verified that the proposed ABM-EMTP method enables high accuracy with larger simulation time steps, significantly improving the simulations’ overall computational performance. It is also shown that the small-signal stability of the system can be accurately assessed using the developed ABMs, including the frequency-coupling dynamics and oscillations.

Discrete detailed models of high-frequency switching voltage source converters (VSCs) are accurate but computationally expensive in simulations of large power-electronics-based systems. For fast/efficient studies, the average-value models (AVMs) of VSCs have proven indispensable, which conventionally utilize controlled voltage/current sources to interface with external circuits. In nodal-analysis-based electromagnetic transient (EMT) simulation programs with a non-iterative solution, the interfacing variables are computed based on the values of input voltages/currents calculated at the previous time step. This delay may cause numerical inaccuracy and/or instability at large simulation time steps. Recently, a so-called directly-interfaced AVM (DI-AVM) has been developed for VSCs that avoids this delay. In this paper, the formulation of the DI-AVM is generalized for an arbitrary configuration of the interfacing nodes. This is done by formulating the extended equivalent conductance matrix for the VSC AVM, assuming all nodes are floating. The generalized conductance matrix is then merged into the overall network nodal equation. The extended DI-AVM is verified in PSCAD/EMTDC against the traditional dependent-source-based AVMs under both balanced and unbalanced conditions and is demonstrated to outperform the conventional AVMs in terms of numerical accuracy at large time steps.