Research On Combinatorial Topology Of Interleaved PFC And Resonant Soft Switching High Frequency Isolated Converters

In some applications such as power supplies for telecommunications,battery chargers for electrical vehicles,galvanic isolation is often required for safety considerations.Transformers are often used in the power electronic circuits to offer galvanic isolation,and there are two kinds of transformers classified by the operating frequency: the power-frequency transformer and the high frequency transformer.The input voltage of the power-frequency transformer is 50/60 Hz AC voltage,while the high frequency transformer is often used in the high frequency switching power supply.The size and weight of the power-frequency transformer is much bigger than the high frequency transformer under the same power rating as the higher operating frequency,the smaller and lighter the transformer will be.Therefore,the converters with high frequency isolation are more widely used in the applications where there are limitations on the size,weight and power density.Firstly,chapter 2 in this paper studies two different kinds of high frequency isolated converters including the resonant DC-DC converter and the phase shift full bridge converter.A hybrid modulated dual output converter is proposed in chapter 2.The power switches in the proposed converter can achieve soft-switching operation by the existence of the resonant tank,and the dual outputs of the proposed converter can be regulated indepently without cross regulation.Secondly,chapter 3 in this paper investigates a high-frequency isolated two-stage AC-DC converter which is consisted of an interleaved totem-pole bridgeless PFC rectifier and a LLC resonant DC-DC converter.Chapter 3 deduces the input current ripple of the interleaving operation in detail,it can be concluded from the deduction that the input current ripple is reduced by the interleaving operation and the frequency of the current ripple is doubled which will get a better EMI performance.The traditional analysis method of LLC resoant converter is fundamental harmonic approximation(FHA)which only considers the fundamental harmonic and neglects the high order harmonic during the power transfer,and FHA has an error because of the neglection of high order harmonic.Chapter 3 introduces an accurate solution of the LLC resonant converter based on the differential equation of the LLC resonant converter.And it is more accurate than FHA.Finally,a MATLAB/Simulink simulation model and an experimental prototype has been built to verify the theoretical analysis,and both of the simulation and experimental results match well with the theretical analysis.Thirdly,chapter 4 proposes an interleaved single-phase single-stage AC-DC converter with high frequency isolation.Compared with the high-frequency isolated two-stage AC-DC converter,the resonant tank is directly connected to the totem-pole bridgeless PFC rectifier,and the high frequency pulsating voltage of the resonant tank comes directly from the PFC rectifier.The proposed single-stage AC-DC converter can get a unity power factor along with a regulated dc output voltage with high frequency isolation by only one stage power conversion.The power switches on the primary side can achieve ZVS(zero voltage switching on)and the diodes on the secondary side can achieve ZCS(zero current switching off).The proposed single-stage AC-DC converter can reduce the number of the power switches and all the power switches can achievesoft-switching operation,which can reduce the switching losses and increase the efficiency.The control strategy,operating principles and operational modes of the single-stage AC-DC converter is analyzed.The frequency response of the LLC resonant tank is analyzed and it is shown that the LLC resonant tank acts as a high pass fiter which attenuates the low frequency component and passes through the high frequency component.An analysis method based on differential equation of the LLC resonant tank by pulse width modulation is presented,and the voltage stress of the intermediate capacitor is calucated based on the proposed method.A MATLAB/Simulink model and an experimental prototype are built to verifty the feasibility of the proposed converter,and both of the simulation and experimental results match well with the theoretical analysis.A comparison has made between the two-stage AC-DC converter and the proposed single-stage AC-DC converter,which shows that the proposed single-stage AC-DC converter has higher efficiency than the two-stage AC-DC converter.Finaly,chapter 5 proposes an interleaved three-phase single-stage rectifier with high frequency isolation.Unlike the two-stage three-phase high frequency isolated AC-DC converter,the three-phase resonant tank is directly connected to the three-phase rectifier,and the high frequency pulsating voltage comes directly from the three-phase rectifier.Just like the proposed single phase single-stage AC-DC converter in chapter 4,the proposed three-phase single-stage AC-DC converter can get a unity power factor along with a regulated output voltage with high frequency isolation.While the resonant current can be reduced by the three-phase resonant tank.All of power switches can realize soft-switching operation.Similarly to the analysis in chapter 4,the LLC resonant resonant tank acts as a high pass filter which attenuates the low frequency component and passes through the high frequency component.And the steady state analysis of the LLC resonant tank is used to calculate the voltage stress of the intermediate capacitor.Finally,a simulation model and experimental prototype are built to verify the feasibility of the proposed converter.Both of the simulation and experimental results match well with the theoretical analysis.Above all,this paper mainly focuses on the research of high frequency isolated softswitching converters.Firstly,this paper analyzes two different kinds of high frequency isolated converters including the resonant DC-DC converter and the phase shift full bridge converter.A hybrid modulated dual output DC-DC converters is proposed.And then,this paper analyzes the high frequency isolated AC-DC converters whose front-end stage is an interleaving PFC rectifier following with a LLC resonant converter.This paper proposes single/three phase single-stage ACDC converters with high frequency isolation,and analyzes the frequency response of the LLC resonant tank and the steady state analysis of the LLC resonant tank.Finally,both of the simulation and experimental results match well with the theoretical analysis,which verify the feasibility of the proposed converter and the correctness of the theoretical analysis.