Three-port Multifunctional Three-level AC/AC Converter With Self-following Flying Capacitor

Three-level(TL)AC/AC converter can be used in high-voltage and high-power applications,for the advantages of low voltage stress of the switches,high conversion efficiency,and small volume and weight of the filter etc.In this paper,the three-port multifunctional AC/AC converter is proposed and studied,focusing on the topology construction,working principle and control strategy of the three-port multifunctional TL AC/AC converter with self-following flying capacitor.The prototype of the converter is developed for experimental verification.Firstly,based on the analysis and research of Buck,Boost and Buck-Boost two-level AC/AC converters,a three-port multifunctional basic circuit is proposed.By changing its input and output ports,Buck type,Boost type and Buck-Boost type AC/AC converters can be obtained,respectively.Combining multilevel technology and three-port multifunctional basic circuits,a three-port multifunctional TL AC/AC converter is proposed and studied.Secondly,the limitations of the control strategy of the existing three-level AC/AC converter is analyzed in detail.The three-port multifunctional TL AC/AC converter with self-following flying capacitor is proposed,and the voltage of the flying capacitor can self-follow the secondary voltage of the small capacity auxiliary transformer without regulating by other control circuits.The proposed converter only needs to control its output voltage,which makes control strategy simple and easy to be realized.Compared with single-function AC/AC converter,the proposed multifunctional converter increases the variety of circuit functions and expands the range of input and output voltages..In addition,the working principle of the three-port multifunctional TL AC/AC converter with self-following flying capacitor operating in Buck,Boost and Buck-Boost function modes is analyzed in detail,and the relationship between input and output voltages is derived.The control strategies of function mode selection control and closed-loop control of output voltage are described in detail.The component parameter selection and circuit design of the main circuit and control circuit of the experimental prototype are given.Finally,a prototype of the three-port multifunctional TL AC/AC converter with self-following flying capacitor is developed and studied.The experimental results verify the correctness and feasibility of the topology and control strategy of the three-port multifunctional TL AC/AC converter with self-following flying capacitor.