Novel reversible boost rectifier with unity power factor

A boost-driven high-power-factor ac/dc converter is proposed. It possesses a bi-directional power flow capability. A bias capacitor connected in series with the ac source provides a dc voltage boost at the input. Thus, a voltage that is always positive is applied at the input of a conventional boost dc/dc converter. A bi-directional dc/dc boost converter is employed to couple the ac side with the dc output. This converter may be controlled to draw sinusoidal average current at the ac side that is either in phase or 180° out of phase with the ac source. Hence, it can provide either unity power factor rectification or inversion. The topology was employed for the design of an ac/dc battery charger with a unity power factor for rated power of 6 kVA. IGBT devices with anti-parallel diodes are used as switches. The efficiency achieved was over 90% and the THD of the input current under 1.8%. This topology is superior to the conventional diode bridge rectifier followed by a dc/dc boost converter in the following points of comparison: (a) removal of the diode bridge eliminates crossover distortions that are inevitable in a conventional Active Power Factor Correction (APFC) circuit with diode rectification bridge at its front end; (b) removal of the diode bridge and usage of two bi-directional switches allows for bi-directional instantaneous power flow which makes possible operation in the inversion mode, in which power is transferred from the dc source to the ac source; (c) at any instance of time only one semiconductor device conducts (as opposed to three or two in conventional rectifiers), which results in higher efficiency.