Oscillation Analysis and Damping Control for a Proposed North American AC-DC Macrogrid

TL;DR

This work analyzes small-signal stability risks in a proposed North American EI–WI MTDC macrogrid with high inverter-based resources. It develops a custom MTDC dynamic model integrated with industrial EI/WI models, conducts modal analysis to identify poorly damped inter-area modes, and demonstrates MTDC-based supplementary damping controllers using wide-area frequency feedback and a data-driven frequency-scanning approach. The study finds critical low-damping modes in EI ($\sim0.84$ Hz) and WI ($\sim0.74$ Hz) that arise from MTDC coupling and grid-forming IBRs, and validates damping improvements using SDCs at Seattle ($WI$) and Minneapolis ($EI$) under base and contingency scenarios. The results highlight a practical, data-driven pathway to enhance inter-area damping in large-scale HVDC macrogrids, with implications for reliable cross-region transmission and system resilience.

Abstract

In recent years, several studies conducted by both industry and U.S. Department of Energy (DOE)-funded initiatives have proposed linking North America's Eastern and Western Interconnections (EI and WI) through a multiterminal DC (MTDC) macrogrid. These studies have explored the advantages and opportunities of the proposed configuration from the perspectives of capacity sharing and frequency support. However, the potential challenges of small-signal stability arising from this interconnection have not been thoroughly examined. To address this gap, detailed model-based simulation studies are performed in this paper to assess the risks of poorly damped inter-area oscillations in the proposed macrogrid. A custom-built dynamic model of the MTDC system is developed and integrated with industry-grade models of the EI and WI, incorporating high levels of inverter-based energy resources. Through model-based oscillation analysis, potential shifts in inter-area modes for both EI and WI, resulting from the MTDC integration are characterized, and modes with inadequate damping are identified. Furthermore, to mitigate the risks of unstable oscillations, supplementary damping controllers are designed for the MTDC system, leveraging wide-area feedback to modulate active power set points at selected converter stations. A frequency scanning approach is employed for data-driven model linearization and controller synthesis. The damping performance is evaluated under the designed operating conditions and selected contingency scenarios.

Figures (11)

• Figure 1: (a) Single-line diagram of MTDC macrogrid showing the scheduled power exchanges between the EI and WI systems, (b) control block diagram for the EI, WI, and MTDC-SDC interaction, and (c) schematic of the SDC (with the constituent blocks) for MTDC power modulation control.
• Figure 2: Bus frequencies from different locations in EI following a 1500 MW dynamic brake insertion event in New England.
• Figure 3: Bus frequencies from different locations in WI following a 1200 MW dynamic brake insertion event in Washington.
• Figure 4: Modeshapes of (a) EI Mode 1, (b) EI Mode 2, and (c) EI Mode 3, estimated from the disturbance data.
• Figure 5: Bus frequencies from IESO and MP, illustrating EI Mode 3 as excited by multiple dynamic brake insertion events in the EI system.