Koen De Gussemé

Digitally controlled boost power-factor-correction converters operating in both continuous and discontinuous conduction mode

Whereas power-factor-correction (PFC) converters for low-power ranges (less than 250 W) are commonly designed for operation in the discontinuous conduction mode, converters for higher power levels are operated in the continuous conduction mode. Nevertheless, when these converters are operated at reduced power, discontinuous conduction mode will appear during parts of the line period, yielding input current distortion. This distortion can be eliminated by employing a dedicated control algorithm, consisting of sample correction and duty-ratio feedforward. The reduction of the harmonic distortion of the input current and the increase of the power factor are demonstrated by experiments on a 1-kW boost PFC converter.

Input-Current Distortion of CCM Boost PFC Converters Operated in DCM

When power-factor correction (PFC) converters designed for operation in continuous-conduction mode (CCM) at full power are operated at reduced load, operation in discontinuous-conduction mode (DCM) occurs in a zone that is close to the crossover of the line voltage. This zone will gradually expand with decreasing load to finally encompass the entire line cycle. Whereas, in CCM, the parasitic capacitances of the switches only cause switching losses, in DCM, they are a source of converter instability, resulting in significant input-current distortion. In this paper, this source of input-current distortion is analyzed, and a solution is proposed. Experimental results are obtained using a digitally controlled boost PFC converter, which is designed to operate in CCM for 1 kW

A Boost PFC Converter With Programmable Harmonic Resistance

Power factor correction converters with low harmonic input resistance are desirable loads to support the reduction of the harmonic distortion on the feeding grid. Therefore, a novel control strategy is proposed. Whereas previously proposed controllers tried to obtain a resistive behavior of the converter with a constant input impedance for all frequencies, including the fundamental, the proposed control strategy allows to set a harmonic input resistance independent of the fundamental input impedance. Consequently, the harmonic input resistance remains low, even when the input power of the converter is decreased. This paper describes the operation of a digitally controlled boost PFC converter with the new control algorithm. Experimental tests on a 1 kW prototype show that a practical realization of the algorithm is possible and that a programmable harmonic input resistance of the converter is obtained