Integrated Design and Performance Evaluation of a Low-Voltage DC Distribution System Using Renewable Energy Sources

This paper presents the technical design and simulation-based performance evaluation of a low-voltage direct current (LVDC) distribution system for residential applications in Colombia. A hybrid architecture, in which a medium-voltage alternating current (MVAC) network supplies a centralised AC/DC converter feeding a 120 V DC residential network, is compared with a conventional AC distribution system. The design is evaluated in DIgSILENT PowerFactory through load-flow, harmonic, and short-circuit studies, the latter based on root-mean-square (RMS) simulations. At 500 m, and with the DC feeder operated hypothetically at the same voltage as the AC system (208 V), conductor losses were 0.506 kW in the DC section versus 1.608 kW in the AC system (about 69% lower); this reduction largely reflects the lower resistance of the selected DC feeder, which uses two conductors per pole, so it is specific to the feeder designs compared, and at the 120 V design voltage the DC losses are comparable to those of the AC system. As converter penetration increased, the voltage total harmonic distortion (THD) of the hybrid system remained between 4.0% and 4.3%, whereas in the AC system it rose from 1.63% to 8.77% with twelve photovoltaic (PV) inverters, with the final tuned filter and the default converter models of the simulation. Conversely, under dynamic loads the hybrid system required about 1.4 s after fault clearing to recover above 0.9 p.u., whereas the AC system recovered almost immediately. In the short-circuit study, the converter was modelled at ten times its 40 kVA design rating, which represents a conservative scenario for protection sizing; the simulated DC and AC fault-current magnitudes are therefore not directly comparable. In addition, the direct conversion from 208 V AC to 120 V DC assumed in the design would require a lower transformer secondary voltage or an additional DC/DC stage. These preliminary, simulation-based results should be confirmed with detailed electromagnetic transient models. Under the operating conditions and modelling assumptions considered, the hybrid architecture therefore offers better harmonic performance and, for the selected feeder designs, lower conductor losses, at the cost of more demanding protection and fault-recovery requirements.