This paper analyzes high-frequency interactions between a Modular Multilevel Converter (MMC) and High Voltage Direct Current (HVDC) grid resonances by studying their effect on the system stability. The recent appearance of converter-related instabilities due to high-frequency oscillations at the converter's ac side raises concerns about whether similar interactions can also take place at its dc side. To determine the risks imposed by such interactions within an HVDC grid, this paper assesses the impact of the MMC internal dynamics and dc system resonances on the stability using an analytical impedance-based method. The effect of fault current-limiting inductors, grid topology changes and transmission line length is investigated, indicating that these parameters considerably influence the electromagnetic characteristics of the HVDC grid and consequently the system stability. Furthermore, a sensitivity analysis of the MMC internal controller dynamics on the converter's non-passivity, causing the instability, is performed.@en

This paper presents a generalized impedance-based modeling framework for harmonic stability assessment due to converter interactions in hybrid AC/DC power systems, relying on detailed analytical frequency-dependent component models. The methodology proposed and derived in this paper enables the stability analysis of complete hybrid AC/DC power systems by explicitly accounting for the effect of both AC and DC systems, leaving out commonly applied simplifying assumptions for one of the two systems. The AC power system is modeled using a generalized transformation from three-phase variables in the ABC frame to a single dq-frame, enabling the representation of cables, overhead lines etc. while preserving inherent model complexities. The methodology is illustrated by presenting models for passive network components as well as for the modular multilevel converter (MMC), and by incorporating them in an example point-to-point High-Voltage Direct Current (HVDC) link.@en

This paper introduces a complete modeling framework for harmonic stability assessment starting from ABCD parameters. It does so by presenting the theoretical foundations for modeling power system components in the ABCD domain, developing adequate interconnection methods for the components, as well as determining the ABCD parameters from any port in the system. The paper also illustrates how the resulting ABCD component models can conveniently be used for a stability analysis of an entire system, consisting of both active and passive components.@en

This paper introduces a complete modeling framework for harmonic stability assessment starting from ABCD parameters. It does so by presenting the theoretical foundations for modeling power system components in the ABCD domain, developing adequate interconnection methods for the components, as well as determining the ABCD parameters from any port in the system. The paper also illustrates how the resulting ABCD component models can conveniently be used for a stability analysis of an entire system, consisting of both active and passive components.@en

This study presents the initialisation of a hybrid alternating current/direct current (AC/DC) power system to determine the operation point around which the system is linearised as a starting point for an electromagnetic or harmonic stability analysis. To this end, each AC or DC power system component is modelled in the Fourier transform domain and further adjusted to a simplified representation compatible with a power flow formulation. The study also presents how voltage source converter (VSC) high-voltage DC-based systems can be analysed when the different VSC controls are applied. The result of the power flow solution is then used for the power converters’ initialisation.@en