Frequency-Dividing-Type Three-Phase Inverter with Adjusting Capacitor

Frequency-dividing three-phase inverters, which consist of a single-phase square wave inverter and a three-phase ferroresonant circuit, have excellent efficiency, constant voltage characteristics, and three-phase balance. These advantages make them suitable for use as dc-ac converters and uninterruptible power supplies (UPS). However, when such three-phase inverters are used as UPS devices, a startup circuit with a complicated sequence is needed to reduce the capacitance of the single-phase inverter. If the sequence is simplified a separate problem emerges¿the phase sequence of the voltage cannot be determined. In this work, the relationship between circuit imbalance and the phase sequence of three-phase voltages is clarified through both experiments and analyses. The results provide useful information on circuit constants which can be used to reduce costs through simplification of startup circuits for these applications.