Single-Input–Single-Output Feedback Control Model and Stability Margin Analysis for Hybrid Dual-Infeed HVDC System

To quantitatively investigate the system stability margin and provide systematic design guidance for the hybrid dual-infeed high-voltage direct current (HVdc) system, this article develops a dynamic multi-input-multi-output (MIMO) transfer function model for the hybrid dual-infeed HVdc system, consisting of a line-commutated converter-based HVdc (LCC-HVdc) link and a modular multilevel converter-based HVdc (MMC-HVdc) link located in close mutual proximity at the receiving side. Then, based on the individual channel analysis and design (ICAD) theory, the equivalent single-input-single-output (SISO) feedback control model is developed without structural information loss, which has the advantage of quantitative evaluation for the system stability margin. Then, the impacts of the ac system strength and control system on the system stability margin are quantitatively evaluated by gain margin (GM) and phase margin (PM) indexes based on the derived SISO model. Moreover, the coupling effect between the ac system strength and the control parameters is also studied. The obtained results from the theoretical analysis and the detailed electromagnetic transient (EMT) simulation in PSCAD/EMTDC validate the accuracy of the derived SISO feedback control model and the correctness of the theoretical findings.