Design Limits of Voltage Unbalance Mitigation in Passive Single-Phase to Three-Phase Converters via Transformer Tap Optimization

Passive single-phase to three-phase conversion represents an attractive alternative for low-power applications, particularly in isolated systems and rural electrification scenarios where simplicity, robustness, and low cost are essential. However, these passive topologies inherently produce voltage unbalance whose magnitude strongly depends on load characteristics. This work analyzes a passive single-phase to three-phase converter based on reactive elements and a transformer, focusing on the limits of voltage unbalance mitigation through discrete transformer tap optimization. The study is conducted under steady-state sinusoidal conditions using phasor modeling and symmetrical component analysis. The voltage unbalance factor (VUF) is adopted as the primary optimization metric, while the current unbalance factor (IUF), neutral current, and converter losses are used as complementary performance indicators. Results indicate that transformer tap optimization can reduce voltage unbalance for specific load conditions, although low residual unbalance is achieved only near the nominal operating point. Higher residual unbalance is observed as the load becomes more inductive within the investigated power-factor range. The findings indicate that passive single-phase to three-phase conversion can be technically viable for low-power applications with relatively stable load conditions. However, applications requiring high power quality or dynamic regulation may benefit from active converter solutions based on power electronics.