Inverter-interfaced distributed generation (DG) is increasingly deployed on distribution networks to enhance voltage support and reduce losses, but optimal siting and sizing on unbalanced three-phase feeders remains a complex challenge. Unlike traditional planning methods that treat all phases identically, this research addresses the practical reality that voltage problems and demand vary by phase, particularly in areas with asymmetric loads.
Researchers developed a constructive Volt/VAR planning algorithm that sequentially places DG units based on phase-specific voltage deficiencies and local demand. The method incorporates a reactive power feasibility test to reject configurations that would cause convergence failures, overvoltages, or further voltage degradation. Using automated three-phase unbalanced power-flow analysis, the approach was validated on two networks: the IEEE 13-node benchmark feeder and the 3,849-bus CHIRIPA system in Honduras.
Results were striking. On the IEEE feeder, annual energy losses fell by 25.8 to 26.4 percent depending on active power allocation assumptions. However, physical capacity constraints prevented all phase voltages from reaching the standard 0.95–1.05 per-unit range. The CHIRIPA network, with more deployment options, achieved full voltage compliance at peak load, though benefits were seasonal—improvements persisted only during daylight hours when solar generation was available. Annual losses there declined by 15.1 to 18.7 percent.
Economically, feasibility in CHIRIPA hinged primarily on total installed capacity (approximately 6.5–6.6 MW over a 25-year horizon) rather than the number of individual units deployed. This insight simplifies project evaluation for utilities and investors planning DG portfolios.
The framework's reproducibility and incorporation of real technical constraints—three-phase unbalance, local interconnection rules, and economic horizons—make it practical for distribution planners worldwide. It provides utilities with a systematic tool for maximizing DG benefits while maintaining grid stability and meeting interconnection standards.
