Storage & DC

This page covers the DC and storage domain: study.dcFlow - the steady-state DC load flow solved by Newton iteration on the nodal current balance F(V) = sum g(Vi - Vj) + sum P/Vi - sum I_src(Vi) = 0, with cable resistance R = r per km x length x loop factor (default 2 for the go-and-return pair), constant-power chargers, Norton equivalents for sources, voltage-device regulation, branch I2R loss, ampacity utilisation and an explicit voltage-collapse flag instead of a fabricated number; and study.evChargingCluster - the EV charging cluster study that combines operating cases (night slow 0.70, day fast 0.30, peak mixed 0.85 concurrency - engineering typical values, not code values) and solves the real load flow for each case to report branch overload, bus voltage drop, THD against GB/T 14549 / IEEE 519 and the harmonic spectrum of the chargers (GB 50966-2014 and GB/T 51313-2018 are conceptual references for the demand factor).

DC subsystems are now designed in their own right (storage, DC fast charging, PV DC collection) and they fail in a way AC studies do not show: a constant-power load can drive the DC bus into voltage collapse. At the same time the cluster of EV chargers is the single largest new load on most LV schemes, so its simultaneity, voltage drop and harmonic distortion decide the transformer and cable rating - all three are evaluated here instead of assumed.

Input = DC topology (dcBus, dcCombiner, dcCable with length/section/material, chargers, sources) plus studyOptions.enableDcNetwork / enableEvChargingCluster. Chain for the DC flow: cable conductance g = 1/R with R = r per km x km x loop factor, Norton source current (E - V)/R for Thevenin sources and P/V for constant-power elements; Newton solves J dV = -F with the analytic Jacobian (d/dV of P/V is -P/V2) until convergence, then every node, branch and source is reported with its loss and utilisation. Chain for the EV cluster: concurrency per charger to kW per charger, grouped by connection point, then one real load-flow solve per operating case, a harmonic scan for the spectrum and the limit tables for the verdict. Outputs: study.dcFlow[] / dcFlowBranches[] / dcFlowSummary (min and max DC voltage, worst deviation, loss and loss ratio, convergence flags) and study.evChargingCluster (worst case, total EV kW, overload count, voltage failure count, THDi). Linkage: charger kW and concurrency move the transformer loading, the loss table and the annual bill on the economics page; DC cable section moves R, the drop and the loss; the SOC window moves the storage dispatch and the replacement cost.