Stability assessment and mitigation HVDC converter interactions

Project Summary

The rapid growth in the amount of converter-interfaced renewable sources and HVDC transmission links is significantly changing the characteristics of the GB grid. The wide timescale control dynamics of converters located in close vicinities can result in coupled effects among the converters and power networks, and can lead to oscillations across a wide frequency range. Accurate assessment of potential system interactions is critical for ensuring stable operation of future and evolving GB network.

This project will develop frequency domain models of HVDC converters and representative network considering future HVDC deployment in the GB network for stability analysis. Time-domain RTDS simulation will be used to validate the theoretical analysis and assessment.

Remedial converter control actions that aim to mitigate instability and resonance will be investigated. Recommendations for specifications of converter models and advice to specific HVDC projects on stability will be proposed.


Key Outputs [Please click links below to access technical reports]

This journal paper published in the IEEE Journal of Emerging and Selected Topics in Power Electronics, Oct. 2020: “MMC Impedance Modelling and Interaction of Converters in Close Proximity”.

Abstract- This paper develops a small-signal impedance model of modular multilevel converters (MMCs) using harmonic state space (HSS) method and studies the stability in a multiple converter scenario. In order to simplify analysis on the coupling characteristics between different frequencies in MMCs, the proposed model is developed in the positive-negative-zero (PN0) sequence-frame, where the zero-sequence current in three-phase three-wire system is directly set to zero without introducing complicated method. A simple 2 by 2 admittance matrix in PN0-frame is extracted from the MMC small-signal model for ease of system stability analysis. Using the developed impedance model, the multi-infeed interaction factor (MIIF) measure is adopted to analyze the most significant interactions for multi-infeed converter systems to be prioritized. Different outer-loop controllers are adopted and compared in the analysis to illustrate the effect of different control modes on converter impedance and system stability. Analytical studies and time-domain simulation results are provided to validate the proposed model and stability analysis.

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