A Novel Three-phase AC-AC Converter Based On Switched-capacitor And Dual-buck Converter

Auto-transformer in distribution have been widely applied in residential and industrial systems as critical devices that adjust the voltage levels between the electric grid and equipment,and with the expansion of distribution network capacity and the diversification of power load,the proportion of which increases.As a traditional electromagnetic transformer,it has the advantages of simple structure,high efficiency and good economy,However,it suffers from the heavy weight of the magnetic core and difficult voltage regulation.The rise of power electronic technology provides an opportunity to solve such problems.Therefore,the research on the power electronic substitutes of traditional auto-transformer has great application value.Considering the advantages of switched-capacitor converter（SCC）in the field of AC-AC fixed frequency conversion,A novel three-phase AC-AC converter（SCDB-AC）based on switched-capacitor（SC）and dual-buck converter（DBC）is proposed in this paper to replace the traditional auto-transformer in distribution network.The converter combines the working characteristics of two parts of the circuit,which inherits the advantages of SCC,such as high step-down ratio and easy modular expansion,and it realizes the linear regulation of output voltage by using the post-stage circuit,and the range of voltage regulation is not limited by the operating efficiency.Then it can ensure the stability of three-phase output voltage by a simple control strategy without phase-locked.At the same time,it adopts two quadrant switches（TQS）to realize AC-AC conversion,which reduces the number of switches employed in the power circuit and avoids the problem of commutation.The specific work of this paper is as follows:First of all,the structure and operation principle of the novel three-phase AC-AC converter were presented in detail,the flexible regulation of output voltage was realized through the design and application of two-stage power conversion and dead-zone-free control.Then,the output gain expression of the converter and the equivalent circuit model considering parasitic parameters were derived,and the characteristics of the circuit parameters of the model were described in detail.In addition,the control strategy of the converter was given,and the voltage detection method and the control loop in the block diagram were explained respectively.Secondly,the the design method of key parameters of the converter were discussed.Then the characteristics of the converter were reflected clearly through comparison with several structures.In addition,the problems of converter circulation and input current distortion were discussed and corresponding improvement schemes were given.Finally,combined with two typical application scenarios of the converter,an experimental prototype with input voltage level of 380 V,power level of 3.5k W was built,and a simulation circuit with input voltage level of 5k V,power level of 10 k W-20 k W was built to verify the correctness and feasibility of the proposed topology structure.