Analytical methodology to develop frequency-dependent equivalents in networks with multiple converters

Abstract

This paper discusses the analysis of dynamic interactions above the fundamental frequency in networks with high penetration of converters. For this purpose, interaction studies require a good representation of network resonances and converter dynamics. However, current methodologies present some limitations in this respect. On one hand, the harmonic impedance obtained from the frequency scan in software does not consider the influence of converter control dynamics. On the other hand, typical stability studies consider those at the cost of simplifying the network representation. The increasing penetration of converters in the network arises concerns due to their limitation in accurately capturing the instability. This paper demonstrates the impact of control interactions in a meshed network with several converters and how this interaction influences the network resonances. Due to the limitations of existing methods, the paper presents a systematic method to capture the relevant dynamic phenomena.

Stability Analysis of High-Frequency Interactions Between a Converter and HVDC Grid Resonances

“…This study showed that a low-frequency unstable oscillation appearing in the system was related to the dynamics of the outer control. In [14], dynamic interactions above the fundamental frequency were analyzed in an ac network with high penetration of MMCs, indicating the risk of unstable interactions in the high-frequency range. In [15], the interaction between an MMC-based HVDC link and an offshore wind farm was studied, showing the importance of the onshore station and dc cable dynamics for analyzing the harmonic stability of the offshore ac system.…”

Generalization of Harmonic State-Space Framework to Delayed Periodic Systems for Stability Analysis of the Modular Multilevel Converter

“…In addition to the aforementioned time-delay behavior, the MMC also exhibits a steady-state time-periodic behavior, which complicates its stability assessment. In the literature, the time-periodic behavior of the MMC has at times been disregarded or simplified by neglecting part of internal converter dynamics [6], [7]. However, such simplifications result in models of limited accuracy from low to intermediate frequencies [8].…”

Impedance-Based Modelling of Hybrid AC/DC Grids With Synchronous Generator for Interaction Study and Dynamic Improvement

“…The impedance modelling methodology has been further extended to analyse the resonance and stability issues specific to wind power plants connected via converters and real experiences have highlighted critical interactions between wind farms controls and HVDC converters [20][21][22][23]. Whereas, [24] derived the analytical impedance equivalents for high frequency analysis, however without the consideration of synchronous generation. Impedance models have been well-applied to stability analysis, but not interaction analysis and dynamic responses considering hybrid AC/DC grids.…”