Planning and Evaluation Method of MMC-MTEDC Network Construction of Urban Power Grid

With the accelerating urbanization process, the load demand of urban power grids is constantly increasing, giving rise to a batch of ultra-large urban power grids featuring large electricity demand, dense load distribution, and tight construction land constraints. This paper establishes a network planning method for urban power grids based on series reactors and MMC-MTEDC, focusing on four aspects: short-circuit current suppression, accommodation of external power supply, flexible inter-regional power support, and voltage stability enhancement in load centers. It proposes key indicators including node short-circuit current margin, line thermal stability margin, maximum fault-induced regional power loss, and voltage recovery time, thereby constructing an evaluation system for MMT-MTEDC network planning in urban power grids. Based on the Shenzhen power grid planning data, simulations using DSP software reveal that series reactors reduce short-circuit current by up to 5.0%, while the MMC-MTEDC system enhances node short-circuit margins by 4.2–12.9% and shortens voltage recovery time by 19.8%. Additionally, the MMC-MTEDC system maintains 3.34–6.76 percentage points higher thermal stability margins than conventional AC systems and enables complete avoidance of external power curtailment during N-2 faults via power reallocation between terminals. Compared with traditional AC or point-to-point HVDC schemes, the proposed hybrid planning method better adapts to the spatial and reliability demands of ultra-large receiving-end grids. This methodology provides practical insights into coordinated AC/DC development under high load density and strong external power reliance. Future work will extend the approach to include electromagnetic transient constraints and lightweight MMC station designs for urban applications.