A general state-space model of VSC DC-side dynamics

The growing integration of inverter-based resources (IBRs) provides net-zero-emission benefits. However, it also introduces new instability challenges that arise from interactions with the power system or other IBRs. Identifying this phenomenon in advance drives the analysis to methods such as those in the frequency domain, where global information can be gathered. The scientific literature contains many IBR representations that do not consider DC-side dynamics or in which such dynamics are embedded within specific models. This complicates their extraction and use in the representation of other IBRs. This paper suggests a general modeling technique to define DC-side dynamics as a function of AC-side variables and sources. The method is verified against a static synchronous compensator (STATCOM), represented using a switching model. The verification is then extended to an aggregated offshore wind power plant model based on type-4 wind turbines with point-to-point HVDC transmission to shore. The approach provides a fundamental building block defining voltage-source converter DC-side dynamics: a capacitor and two ideal controlled current sources, one for charging and the other for discharging. The model is a nonlinear differential equation with states accessible from the AC side. The simulation results show that it is possible to synthesize the DC dynamics uniquely for the three applications considered, and potential extension for DC systems is possible.