Research On Step-Up Conversion Technology And Its Application Based On Resonant Network

The emergence of new loads such as electric vehicle charging piles requires power electronics engineers to develop novel converters.These converters need to meet the requirements of wide range with higher efficiency and lower cost.Resonant converter is widely used in modern power converter because of its soft-switching characteristics of zero voltage switching(ZVS)and zero current switching(ZCS),and the wide range of input and output.However,at present,resonant converters are mostly used as DC/DC converters,and there are not many researches on using the resonant characteristics of resonant network on step-up AC/DC application.For general AC/DC converter,the application of power factor correction(PFC)greatly improves the power factor and reduces the harmonics flowing into the power grid.Therefore,many general converters use the front-end PFC circuit to make the input current approximately sinusoidal and in phase with the input voltage.However,the front-end circuit increases the volume,cost and loss of the converter.How to realize the power factor correction of resonant circuit without additional circuit needs further investigation.This paper presents a step-up converter based on the resonant network,which can realize the step-up demand of AC/DC circuit.In this circuit,the step-up function is realized by using the resonant characteristics of resonant network.The transformer has only isolation function and the ratio is 1:1,which does not participate in the step-up effect.Besides,due to the resonant characteristics,the soft-switching can be guaranteed to improve the efficiency of the converter.By controlling two groups of switches in the full-bridge of the single-stage converter,power factor correction can be realized without external circuit or the sharing of switches.First,based on the current research status of AC/DC resonant converter;the paper proposes a single-stage step-up AC/DC resonant converter without boost-type,analyzes the topology composition and equivalent circuit of the converter,explains the operating principles for different operating mode with different input voltage,deduces the resonant characteristics of the converter based on the equivalent circuit,and analyzes the operating region of the circuit with variable input voltage based on the gain characteristic curves.The relationship between the phase-shift angle and power of the resonant converter is analyzed.The paper explains the conditions of soft-switching,puts forward the corresponding restrictions combined with the relationship between ZVS angle and frequency,and analyzes the power loss.Then,the converter is modeled for the closed-loop control designing,and the steady-state model and small signal model of the system are obtained.The variable frequency control strategy is designed based on the model and time-domain simulation,and the variable frequency or phase-shifting auxiliary control strategy is added to improve control accuracy.Finally,hardware circuits including main circuit board and control circuit board are designed based on the proposed topology and control strategy,and the software design scheme is provided.Experiments are carried out under different load conditions,different voltage and power levels.The experimental results can verify the feasibility and effectiveness of the topology and control strategy.The converter can achieve stable step-up power conversion,as well as power factor correction and soft switching.