Sepic and Cuk power converters working as power factor preregulators (PFP) in the discontinuous conduction mode (DCM) present the following desirable characteristics for a PFP: (1) the power converter works as a voltage follower (no current loop is needed); (2) the theoretical power factor is unity; and (3) the input current ripple is defined at the design stage. Besides, input-output galvanic isolation is easily obtained. This paper analyzes the operation of both power converters as DCM-PFP. Design equations are derived, as well as a small-signal model to aid the control loop design. Both simulation and experimental results are presented that are in agreement with the theoretical analysis and complement the work.

The discontinuous conduction mode Sepic and Cuk power factor preregulators: analysis and design

Solid-state switch mode AC-DC converters having high-frequency transformer isolation are developed in buck, boost, and buck-boost configurations with improved power quality in terms of reduced total harmonic distortion (THD) of input current, power-factor correction (PFC) at AC mains and precisely regulated and isolated DC output voltage feeding to loads from few Watts to several kW. This paper presents a comprehensive study on state of art of power factor corrected single-phase AC-DC converters configurations, control strategies, selection of components and design considerations, performance evaluation, power quality considerations, selection criteria and potential applications, latest trends, and future developments. Simulation results as well as comparative performance are presented and discussed for most of the proposed topologies.

Comprehensive Study of Single-Phase AC-DC Power Factor Corrected Converters With High-Frequency Isolation

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.

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

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

/pdf/input-current-distortion-of-ccm-boost-pfc-converters-2hhmrfoj00.pdf

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

A systematic analysis of line-current distortions of the discontinuous-conduction-mode and the continuous-conduction-mode boundary boost power factor correction converter due to valley switching (VS) and switching-frequency limitation, where VS is either maintained or lost after the onset of switching-frequency limitation, is provided. Closed-form expressions for the line current are derived. It is shown that if the switching frequency is limited and VS is not maintained, the line current is more distorted with voltage-mode control than with current-mode control. The effects of line-current distortions are demonstrated with both simulation and experimental results.

/pdf/effect-of-valley-switching-and-switching-frequency-1t8b4p16gp.pdf

Effect of Valley Switching and Switching-Frequency Limitation on Line-Current Distortions of DCM/CCM Boundary Boost PFC Converters

The determination of the boundaries between both modes of conduction (continuous and discontinuous) in PWM DC-to-DC switching power converters used as power factor preregulators (PFP) is presented in this paper. When a DC-to-DC switching power converter works as a power factor preregulator, its operating point is constantly changing due to the fact that both the DC voltage conversion ratio and the load "seen" by the power converter are constantly changing in each half-sinusoid of the line voltage (input voltage of the converter). In these conditions, the conduction mode cannot be directly determined. In this paper, the boundaries between both conduction modes in each angle of the half-sinusoidal input voltage have been determined. The conditions to always operate in continuous or in discontinuous conduction modes have been determined as well. Finally, these results have been verified by simulations and experimental results. >

The determination of the boundaries between continuous and discontinuous conduction modes in PWM DC-to-DC converters used as power factor preregulators

J.M. Lopera

Papers

The determination of the boundaries between continuous and discontinuous conduction modes in PWM DC-to-DC converters used as power factor preregulators