Hybrid MIMO method for impedance-based stability analysis of MTDC systems

This paper presents a hybrid multiple-input multiple-output (MIMO) impedance-based method for the small-signal stability analysis at the DC side of modular multilevel converter (MMC)-based high-voltage direct current (HVDC) systems in a multi-terminal (MT) configuration. In such configurations, developing an in-depth understanding about the DC-side stability is getting vital to ensure interoperability between the different converters interacting through the DC network. Doing so, adverse converter-related interactions, of which several real-life events have already been reported primarily at the AC side, can proactively be avoided. A hybrid MIMO method for impedance-based analysis is developed to overcome key drawbacks of the conventional source and load representation for the stability analysis of MTDC systems. Furthermore, a novel frequency-lifted linear time-invariant (LTI) model of the MMC DC-side impedance-based representation is derived to accurately capture frequency coupling effects. The stability analysis is performed with an MMC-MTDC system via the developed method combined with the derived MMC model. A sensitivity analysis with regard to the DC network and MMC dynamics illustrates the impact of fault-current limiting inductors and control scheme modifications on the MTDC system stability. • A novel impedance method is proposed overcomes conventional limitations. • Provides clear insights into impedance method constraints. • Develops frequency lifted MMC modeling for MTDC design & stability. • Highlights the critical impact and importance of frequency-lifted modeling. • Investigates fault-limiting DC inductors’ effect on MTDC stability.