Dynamic Interaction and Small-Signal Stability Assessment of Hybrid AC/DC Grids with High Renewable Penetration (InterAcDC)

• Applicant: Dr.-Ing. Yonggang Zhang
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 517518989

Motivated by the potential converter-driven stability risks from the future massive renewable energy transmission through hybrid AC/DC grids, the project is to identity the possibly unwanted interactions among inverter-based generations (IBGs), synchronous machines (SMs), high-voltage direct-current (HVDC) transmission systems and passive grid components taking into account the bidirectional AC-DC dynamic coupling from HVDC. On this basis, the sources and spreading ranges of the potential arising oscillations are to be determined. Since DC voltage plays the same role of energy balance indicator as the frequency in AC systems, the standard DC voltage (droop) regulation can naturally introduce AC-DC dynamic coupling in (multi-terminal) HVDC. Moreover, as grid-forming control is the future trend for HVDC, the AC-DC dynamic coupling in HVDC is expected to get stronger and to involve more HVDC converters. Therefore, the traditional small-signal stability assessment for HVDC that is conducted either from AC side or DC side while simplifying or neglecting the other side’s dynamics may not yield reliable results for the future hybrid AC/DC grids. The proposed project will thus go one step further by: 1) establishing a more complete system model; 2) examining the applicability of existing stability analysis methods for the stability assessment of future hybrid AC/DC grids; 3) developing the required enhancements to the most promising analysis method, i.e. the nodal admittance matrix based method as applied in our previous work; 4) investigating the stability impacts of various HVDC and IBG control schemes as can be classified into grid-following, grid-forming etc.; 5) developing bidirectional AC-DC dynamic coupling indicators and analyzing their stability impacts.Analytical results will be validated by time-domain stimulations and laboratory tests. Benefiting from the project, the improved system level modelling and enhanced stability analysis method can serve as a basis for the future de-risking study of (multi-vendor) HVDC integration / expansion projects. The findings on the behaviors of the representative HVDC and IBG control schemes, the mechanisms of the negative control interactions involved in the potential arising stability problems, and the stability impacts including high-impacting factors of AC-DC dynamic coupling from HVDC can also be used to estimate and classify future oscillation instabilities and to derive appropriate recommendations for transmission system operators (TSOs) and manufacturers for network planning and product development.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Martin Braun