Power Factor Enhancement of a Soft-Switched Common-Neutral Single-DC-Bus Power Converter

This paper presents an improved control methodology for the rectification stage of the recently proposed high-power-density high-efficiency common-neutral single-dc-bus ac-dc-ac converter suitable for a single-phase online uninterruptible power supply (UPS). The rectification stage operates in boost/buck-boost mode depending on the input line voltage polarity and utilizes boundary conduction mode (BCM) control enabling soft-switching and allowing high frequency operation. The proposed control strategy utilizes a variable on- time control in both operating modes to compensate for sensing delays in the zero-current detection (ZCD) circuit, thus enabling high input power factor and low input current THD compared to the previously presented strategy. An analytical model for the boost and buck-boost converter is also presented which facilitates in the design of the proposed variable on-time controller. A GaN- based 1-kW prototype converter, utilizing the common-neutral single-dc-bus topology, is designed, built, and tested to validate the proposed control technique. The prototype converter maintains a high input power factor of 0.97 across a 4:1 output power range while achieving a peak efficiency of 98.4%.