Quasi Power Factor Correction for High Efficient AC/DC Converter

Abstract

Harmonic pollution and low power factor in power systems caused by power converters have been of great concern. To overcome these problems several converter topologies using advanced semiconductor devices and control schemes have been proposed. This investigation is to identify a low cost, small size, efficient and reliable ac to dc converter to meet the input performance index of UPS. The performance of single phase and three phase ac to dc converter along with various control techniques are studied and compared. This project presents a novel ac/dc converter based on a quasi-active power factor correction (PFC) scheme. In the proposed circuit, the power factor is improved by using an auxiliary winding coupled to the transformer of a cascade dc/dc fly back converter. The auxiliary winding is placed between the input rectifier and the lowfrequency filter capacitor to serve as a magnetic switch to drive an input inductor. Since the dc/dc converter is operated at high-switching frequency, the auxiliary windings produce a high frequency pulsating source such that the input current conduction angle is significantly lengthened and the input current harmonics is reduced. Since the use of a single inductor, the cost z reduced a lot and the efficiency of the system is improved. The power factor is maintained constant by using a buffer capacitor in parallel to the system for compensating the inductive components. It eliminates the use of active switch and control circuit for PFC, which results in lower cost and higher efficiency. Finally an R- load is applied and simulation results are presented