Nonlinear Modular State-Space Modeling of Power-Electronics-Based Power Systems

Power system state-space models are often constructed by interconnection of their subsystems (converters, distribution lines, and grid). The interconnection between L-/LCLfiltered converters with the distribution lines subsystems is often realized through a virtual resistor, because they both have the voltage as input, introducing inaccuracy. Moreover, the parameters variations influence not only the eigenvalues, but also the equilibrium point. In this case, the small-signal model has to be reevaluated around the new equilibrium point. For the computation of the equilibrium point, an additional method, e.g., power flow, is conventionally used. However, the variables computed with power flow (e.g., P, Q, V, and theta) do not always coincide with the state-spacemodel variables, required for the linearization. Furthermore, the traditional power flow does not consider the influence of the voltage-source-converter control system on the grid equilibrium point. This article proposes a nonlinear grid model that does not need the virtual resistor to be interconnected. The proposed model can be used both for equilibrium point computation through the Newton-Raphson method, and it can be linearized around the computed equilibrium point for small-signal analyses. Simulations and experiments are provided.