Localization and Reshaping of Non-Minimum-Phase Zeros in Multi-Converter Systems

A research team from Zhejiang University, led by Huanhai Xin, has published a novel framework addressing a critical stability challenge in modern power grids. The proliferation of renewable energy sources like solar and wind has led to multi-converter systems, where hidden mathematical properties called non-minimum-phase (NMP) zeros impose fundamental ceilings on control bandwidth. The key breakthrough is a Jacobian-based method that decouples these NMP zeros from individual, often proprietary, converter dynamics. It proves the zeros are strictly real and expresses their values solely as singular values of a matrix constructed from the public grid admittance matrix and steady-state power injections, making system-level analysis practical for the first time.

The paper establishes that as the dominant NMP zero approaches the origin, the stability margin degrades unavoidably, quantified by an exponential lower bound on the peak of the complementary sensitivity function. To counteract this, the researchers propose a targeted zero-reshaping strategy. This method ranks converter nodes by their real participation factors to identify the optimal site for deploying voltage droop control without iterative search. By strategically steering the dominant zero away from the origin, the framework suppresses the sensitivity peak, directly improving the grid's stability margin and resilience against disturbances. This provides grid operators with a systematic, data-driven tool to enhance the reliability of increasingly inverter-dominated power systems.