The number of converters connected to the system is likely to be increased. These devices may interact with each other through the network. TSOs are concerned about the impact of these interactions and its influence on the stability. This paper presents the stability analysis of a system with two converters. The problem is studied in the frequency domain by using an impedance-based approach. A model for assessing the closed-loop stability of the complete system is developed. This approach shows to have potential for studying the interactions in larger networks. The relative stability under different grid parameters is addressed. Simulation results show that the stability is compromised when a parallel converter is connected.

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Modern power systems face several problems at frequencies above the range of traditional stability studies due to the increasing penetration of power electronic devices. This phenomenon has been recently referred to as electromagnetic transient stability and is a growing issue in systems with power electronic converters at any power and voltage level, such as FACTS, HVDC, interfaces for grid connection of renewable energies, custom power devices for power quality enhancement, among others. The study of power systems stability is usually carried out by simulation tools that represent the power system through phasor models. However, due to the faster dynamics of modern systems, the harmonic interaction among the controllers, the converters, and the electric power components, recent research results suggest that some stability analysis should be conducted with models suitable for wider frequency ranges, e.g., electromagnetic transient models. This paper reviews the use of frequency domain methods to analyze the influence of the modeling approach of passive power components on the results of electromagnetic transient stability studies.

In this paper, an analysis of electromagnetic instability is presented for Voltage Source Converter High Voltage Direct Current (VSC HVDC) systems. In recent years, the interaction between electromagnetic modes of the system and the converter dynamics has shown to give rise to instability problems in the AC network, up to the kHz range. This paper extends the analysis of the problem to the DC side and investigates to what extent similar problems can be expected in future HVDC installations.