| In recent years,with the development of science and technology,electrical equipments have developed rapidly,such as light emitting diode(LED),brushless DC motor,portable equipment and so on,which have a good prospect.Therefore,due to these electrical equipments needing low voltage supply,power supply with low output voltage has also achieved a good market.Consequently,as the front-end part of power supply,power factor correction(PFC)converters have important research significance.In applications where ultra-low output voltage is required,traditional single-stage PFC converters can only operate in very small duty cycles due to the limitations of their own voltage gain.This is not only a challenge for the controller,which requires a high performance controller,but also making the utilization of the switches in converters very low.In addition,in order to solve the problem of high intermediate bus voltage resulting from Boost PFC converter,researchers have done a lot of research on Buck PFC converter.However,the traditional Buck PFC converter can not meet the relevant harmonic criteria due to the problem of input current dead zone angle,which results in a low power factor(PF).Aiming at the above problems,this paper proposes two series-capacitor based interleaved PFC converters with ultra-low voltage output characteristics,and dose relevant research on them.The series-capacitor based interleaved Buck PFC converter proposed in this paper effectively controls the energy transfered to the load in one switching cycle by adaptively adjusting the charging and discharging time of the intermediate storage capacitor,which realizes ultra-low voltage output to improve the dead zone angle of input current.Besides,the imtermediate storage capacitor operates in discontinuous capacitor voltage mode(DCVM)to realize automatic PFC,whose peak voltage is clamped to the input voltage to solve the problem that the extremely large voltage stress exists in the conventional DCVM PFC converter.In this paper,the working mode and working characteristics of the proposed Buck PFC converter are analyzed in detail,such as the characteristics of input current,ultra-high setp-dowm ratio,capacitor voltage clamp and PF.Then the power loss and critical condition of DCVM are particularly derived.The analysis results show that the converter has ultra-low voltage output characteristic and almost unity PF.Moreover,the critical condition of DCVM is easily met.Another proposed converter in this paper is the series-capacitor based interleaved Buck-Boost PFC converter.Compared with the traditional interleaved Buck-Boost converter,the proposed Buck-Boost converter has a higher step-dowm ratio,namely the characteristic of ultra-low voltage output,which can solves the problems of the extremely low duty cycle and its difficult control of traditional single-stage PFC converter in ultra-low voltage output applications.In addition,the proposed Buck-Boost PFC converter has the characteristic of automatic current sharing,which eliminates the current sharing circuit and its control loop in the traditional interleaved PFC converter and results in a better economic benefits.In this paper,the working mode and working characteristics of the proposed Buck-Boost PFC converter are analyzed in detail,such as the characteristics of voltage transmission gain,automatic current sharing and input current.Then the critical conditions of the inductance value are derived in particular.Moreover,aiming at the problem that negative current of the inductor may occurs due to the unreasonable parameter design,an improved topology is proposed.The analysis results show that the converter also has the characteristics of ultra-low voltage output and automatic PFC.Finally,by constructing the corresponding experimental platform,the two series-capacitor based PFC converters proposed in this paper are simulated and experimented respectively.The experimental results and data are given to verify the correctness of the theoretical analysis. |
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