In-Hwan Oh, Bob Roohparvar, and Justin Chiang
Fairchild Semiconductor

This paper presents a full Digital Power Factor Correction (DPFC) that features a control method based on a Modified Sinusoidal Pulse-Width-Modulation (MSPWM). Specifically, this paper presents Fourier harmonic analysis results of a conventional Discontinuous Current Mode (DCM) boost-type power factor correction and shows the third harmonic problem typically seen with a fixed switching frequency that employs a digital controller. Based on these analysis results, this paper proposes a method of modifying duty control to effectively eliminate the third harmonic.

The harmonic analysis results from the MSPWM method are shown through software simulation. By using proposed the proposed MSPWM with a fixed switching frequency, a good sine current with very low harmonic distortion can be obtained. Furthermore, since the proposed method does not need to sense a line current or voltage, it can be implemented by using a low speed and low priced conventional microcontroller (FMS7401).