The Research On DCM Bridgeless Boost PFC Converter

Nowadays, realizing environmental friendly power supply, reducing harmonic pollution and electromagnetic interference have become a fundamental demand for power system design. Introducing Power Factor Correction(PFC) will effectively promote its input power factor and reduce the influence of current harmonics on the grid, which will guarantee good electricity quality as well as avoid harmonic interference. In current research on PFC technology, the core problem is how to realize high efficiency, high power factor and high power density.Among various devices using PFC technology, rectifier is usually used to convert alternating current to direct current, then correction of power factor is realized by PFC converter. With the increasing of converter power level, the loss proportion ratio of rectifier from the overall loss is constantly increasing, which limits the converter's efficiency dramatically. For this reason, bridgeless PFC, which get rid of rectifier from input side, receives more and more attention from the public.In this paper, the working principle of discontinuous current mode(DCM) of basic bridgeless Boost PFC is introduced and a detail mathematical analysis of its characteristics is provided as well. At the case of fixed frequency and fixed duty cycle, even though Bridgeless Boost PFC working under discontinue current mode has advantages such as simpler control strategy and less switching loss, it still suffers from low power factor when voltage ratio is comparatively large. Based on the analysis above, a 500 W prototype is designed and invented. The advantage of high efficiency has been proved by the experiment, in which the prototype has an efficiency up to 98.5%. But when the input voltage is high, the power factor decrease significantly.In order to improve the low power factor drawback, a simple adaptive duty cycle control strategy is proposed based on the calculation of ideal duty cycle. Compared with constant duty cycle control, the method applied in this paper can raise input power factor, depress the input current ripple and, in the same time, ensure high efficiency. On this basis, adaptive duty cycle control is applied on a 500 W prototype and proved effective by experiment.PFC in discontinuous mode generally apply only to small and medium power applications due to high voltage and current stress. To increase power density and expand its application for high power case, interleaving technology is introduced to bridgeless PFC converter. Working principle and characteristics of the interleaving Bridgeless Boost PFC converter working in DCM mode is analyzed and a 1kW prototype is invented on the analysis.The non-ideal factors, such as parasitic parameters in power devices and non-linear inductance, have significant impact on the circuit characteristics.The influence of the typical non-linear factors in circuit on converter characteristic has been studied by detailed mathematical analysis. The parasitic parameters are considered first to discuss the operation characteristics of the converter. The mathematical relation between parasitic parameters and current distortion are calculated and verified by simulation. Then, use the gyrator-capacitor model to analyze the non-linear inductance in the converter, introduce the calculation method of the model parameter and verified by simulation.