A Family of Single-Phase Hybrid Step-Down PFC Converters
Abstract
The conventional Boost PFC usually suffers from high output voltage and low efficiency at low input condition. Recently, the Buck PFC has attracted a lot of research interests for its low output voltage and high efficiency at low input condition. However, the conventional Buck PFC converter usually has low power factor (PF) and poor harmonic performance due to the inherent dead angle of the input current, especially at low input condition. How to achieve high power factor, low output voltage and high efficiency at the same time is still a big challenge for the PFC converters. This paper proposes a family of hybrid PFC converter topologies combine the advantages of Boost PFC and Buck PFC converters, which feature low output voltage and continuous input current (high PF). The derivation methodology is presented. The experimental results verify the advantages of the proposed topologies.
EXISTING SYSTEM:
Recently, using the buck converter as a front end PFC converter has been introduced. The Buck PFC converter has higher low line efficiency and lower EMI noise compared with the conventional Boost PFC converter. Due to the inherent dead-time in the input current when the input is lower than the output, the Buck PFC usually has limited PF and high current distortion, which may not meet the current harmonic requirement, especially for lighting applications. A lot of researches have been conducted to analyze and improve the PF of the Buck PFC converter by compensating the current during the dead time. But there is still not a systematical derivation methodology to give a thorough insight for these kinds of topologies. In order to solve the issues mentioned above, this paper proposed a family of single phase step-down converter with high power factor. The objective is to combine the advantages of conventional Boost PFC and Buck PFC using hybrid method. And the derivation methodology is discussed. Finally, the experimental results from a proposed topology with universal AC input and 85V output are presented.
PROPOSED SYSTEM:
The conventional Buck PFC converter and its steady state operation waveforms. Compared with the conventional Boost PFC, the Buck PFC has some attractive features, such as low output voltage, low common mode noise, small inductor size, inherent inrush current limitation and high efficiency at low input condition. However, the PF and THD performance are poor due to the discontinuous input current. If we can compensate the input current for a Buck PFC when its input voltage is below its output voltage, the PF and THD will be similar to a Boost PFC while keeping all the other desired features. In order to achieve this, a step-up converter should be integrated in a conventional Buck PFC to compensate the input current during the dead time, which is referred as a hybrid method in this paper. The step-up converter can be a Boost converter or a Buck-Boost converter (also Flyback as its isolated version). Generally, there are two ways to integrate a step-down converter and a step-up converter, i.e. parallel connection and cascade connection.
CONCLUSIONS
As a summary, this paper presents a family of hybrid PFC converter based on Buck converter and Buck-Boost (or Flyback) converter. The proposed topologies features low output voltage, high power factor and high efficiency, which is quite attractive for application with wide AC input range or high AC input. Detailed topology derivation method and design considerations are presented in the paper. Finally, a 100W prototype with universal AC input was built to verify the advantages of the proposed method.
REFERENCES
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