A novel single-stage unity power factor rectifier/inverter for UPS applications

A novel topology for an AC/DC converter is proposed. An input bias capacitor connected in series with the AC mains is employed, which together with an appropriate control allows for removal of the rectification diode bridge. A bidirectional DC/DC Cuk converter is then employed to produce a closely sinusoidal input current while maintaining the bias capacitor voltage such that the sum of line and bias capacitor voltages is always positive. This guarantees the controllability of the input current. The circuit can be controlled so as to reverse the direction of power flow from a DC source to an AC load which makes it appealing for uninterruptible power supply applications. This novel topology was validated using the Saber hybrid simulator in the power range from a few hundred of watts up to several kilowatts. The input current distortion factor is 0.998 and the efficiency over 80%.