Augmented Sequence Impedance Networks of Grid-tied Voltage Source Converter for Stability Analysis
For power electronics engineers analyzing grid-tied VSC stability, this work simplifies the analysis by reducing MIMO impedance models to decoupled SISO systems, though it is an incremental improvement over existing sequence impedance methods.
The paper addresses the complexity of stability analysis in grid-tied voltage source converter (VSC) systems, which typically require Multi-Input Multi-Output (MIMO) impedance models. By viewing the source and load subsystems as an integrated system, the authors derive two decoupled Single-Input Single-Output (SISO) systems called Augmented Sequence Impedance Networks (ASIN), enabling stability analysis using the simpler Nyquist criterion. Numerical and time-domain simulations verify the approach.
Impedance-based stability analysis is appealing in the case of Single-Input Single-Output (SISO) systems. However, in the case of grid-tied voltage source converter (VSC) systems, dq impedances of source and load (VSC) subsystems are typically Multi-Input Multi-Output (MIMO) systems in which case the Generalized Nyquist Criterion (GNC) is required for analyzing the closed loop stability, which increases the complexity of the analysis. This paper explores further the coupling between positive and negative sequence impedances, in particular the dependency and bindings between them. It shows that the couplings in each subsystem can be compounded into two non-coupled sequence impedances if the source and load subsystems are viewed as an integrated system instead of as two separate subsystems. Therefore, two decoupled SISO systems are obtained which are defined as Augmented Sequence Impedance Networks (ASIN). The stability analysis of the closed loop system is performed directly on the ASIN with the principal of Argument. Both numerical and time domain verifications are presented.