On small signal stability of an AC/DC power system with a hybrid MTDC network

• A model of an AC/DC power system with a hybrid MTDC network. The model serves as a unified platform for both time domain simulation and small signal stability analysis (SSSA).
• SSSA is used for the analysis of interactions between generator controls and converter controls.
• Auxiliary power oscillation damping (POD) controllers designed based on the results of SSSA.
• Analysis of the oscillatory modes representing an interaction between the line commutated converter (LCC) and voltage source converter (VSC).

Multi-terminal HVDC (MTDC) networks are being contemplated for large scale integration of renewable energy sources, as well as for the interconnection of asynchronous AC systems. A hybrid MTDC network that combines line commutated converters (LCCs) and voltage source converters (VSCs) can combine the benefits of both technologies. This paper presents a mathematical model of an AC/DC power system with an embedded hybrid MTDC network interconnection. Small signal stability analysis of the power system is conducted based on the linearization of the model. The impact of VSC controller gains on the dominant modes in the system is investigated. The contributions of the converters and generators to different modes of the system are investigated based on the participation matrix analysis. Auxiliary controllers are applied at the converters for the purpose of damping power oscillations in case of disturbances. The results of small signal stability analysis are validated by time-domain simulations in MATLAB.