Cost-Aware Topology and Gun-to-Module Ratio Design for Modular Multi-Gun DC Fast Chargers

Modular multi-gun DC fast chargers can improve converter-capacity utilization by allowing charging guns to share power modules, but additional internal reachability also increases switching devices, layout complexity, reconfiguration exposure, and fault-related burden. This paper investigates topology and gun-to-module-ratio co-design for modular DC fast chargers from a device-level architecture perspective. A unified screening framework is developed to compare fixed, ring, partitioned, and semi-flexible layouts under common demand patterns, coefficient settings, and probabilistic module outages. A normalized cost-aware planning score evaluates delivered charging service against architecture burden, while exact small-scale benchmarks, repeated-seed sweeps, hotspot cases, robustness analysis, and continuous-operation references are combined to separate robust conclusions from conditional ones. The results show that fixed topology is the most conservative and robust option under balanced demand and high switching burden, whereas partitioned topology gives the most statistically regular behavior across broad sweeps. Semi-flexible layouts are not globally superior; their advantage appears mainly under persistent hotspot demand and moderate switching burden. These findings position bounded module sharing as a conditional charger-design regime for hotspot-prone applications. The results apply under homogeneous-module, graph-level, structured-demand, and proxy-cost assumptions and provide planning-stage architecture-screening guidance instead of hardware-calibrated cost predictions.