Novel Single-Stage High Frequency Isolated Multi-Level Inverter Topologies And Topological Derivation Method

Inverter is an electric energy conversion device that converts DC into AC.Multi-level inverter has many advantages such as low power switching tube voltage stress,high output voltage quality,and low electromagnetic interference.Compared with the traditional multilevel inverter,the bidirectional high-frequency isolation multi-level inverter(HFI-MLI)combines high-frequency link technique and multi-level technique,not only have many advantages of multi-level inverter,but also have the advantages of high frequency electrical isolation and bidirectional power flow.At present,bidirectional HFI-MLIs mainly adopt two-stage architecture based on dualactive-bridge.This architecture is composed of high-frequency isolation DC-DC and fullbridge DC-AC.Its advantage is that the high-frequency transformer and the multi-level voltage waveform belong to the front and back stages respectively,which can completely retain the advantages of the multi-level inverter.However,two-stage architecture leads to a large number of power switching tubes.The worse is for each additional voltage level,the number of increased power switches is up to eight.Reducing the number of power switches is conductive to reducing the cost and loss caused by power switches and their driving circuits,and thus improving the efficiency and reliability of the HFI-MLI.To this end,this article fouces on the single-stage bidirectional HFI-MLI,aiming to propose some novel single-stage bidirectional HFI-MLI topologies.Not only the number of power switches is reduced bust also all or part of the power switch voltage stresses.The main contributions of this thesis are as follows:A.A topological derivation method suitable for single-stage bidirectional HFI-MLI is proposed.Although various multi-level inverter topologies have emerged since the multi-level technique was proposed,there are few researches on topology derivation methods.Topological derivation methods are highly subjective and difficult to form a unified methodology,but the research on derivation methods is conducive to the study and comparison of a large number of multilevel topologies,so it has certain research significance.For this reason,this article puts forward a derivation method suitable for single-stage high frequency isolation multi-level inverter topology through the research of various basic topologies.This method takes the construction of multiple independent and controllable current loops as the basic idea,and constructs a variety of multi-level invert units.A novel single-stage bidirectional HFI-MLI topology can be obtained by combining each one of the multi-level invert units with high frequency transformer and cycloconverter.This method can also further derive the existing multi-level topology to more voltage levels with a fewer number of additional power switches.B.Several novel single-stage bidirectional HFI-MLI topology families are proposed.Based on the proposed topology derivation method,a number of novel HFI-MLI topology families are proposed.The proposed topologies do not contain intermediate DC links and have the advantages of high-frequency electrical isolation,bidirectional power flow,and low switching tube voltage stress.The theoretical analysis of the proposed push-pull single-stage bidirectional HFI-5LI topology proves that althought there is a slight increase in the output filter inductance compared with the tranditional five-level invertern in order to ensure the same output voltage quality,the number of employed power switches is reduced by half,and the voltage stresses of most power switches are reduced by 75%.The power switches amount and power switch voltage stresses are further reduced in the proposed flyback single-stage bidirectional HFI-5LI.In addition,a novel multi-carrier modulation strategy and DC-side capacitor voltage balancing strategy are proposed,which expands the feasible range of voltage equalization and enhances the load capacity of the inverter compared with traditional multilevel inverters.C.Simulation and experimental verifications for proposed novel topologies.Simulation models of proposed push-pull and flyback single-stage bidirectional HFI-5LI are built in PSIM.The simulation results prove that the proposed topology has higher output voltage quality and strong load capacity.It also proves the correctness and effectiveness of control strategies.Successfully developed 1000 VA push-pull single-stage bidirectional HFI-5LI prototypes and200 VA flyback single-stage bidirectional HFI-5LI prototypes,and implemented digital closedloop control based on DSP TMS320F28335.Experimental results further verify the correctness and effectiveness of the proposed inverter topology and control strategy.