T Type Five-level Topology And Its Capacitor Voltage Balance Control

Renewable energies,such as photovoltaic and wind energies,are considered as the most important solution worldwide to deal with the challenges from energy security,environment pollution and climate change.With the newly proposed high voltage level PV structure,multi-level converter is getting more and more attention.This paper focuses on a T-type five-level converter,its overall performance and capacitor voltage balance(CVB)control issue.1.T-type five-level topology is introduced from the view of topology combination.Its overall performance like power device losses and inductor demand is compared with NPC three-level,five-level topologies and T-type three-level topology.Results show that T-type five-level topology features low power device losses and small inductor demand in the high power application.2.A hybrid space vector modulation(HSVM)strategy is proposed to keep the capacitor voltage balance in the whole range of modulation rate.Firstly,the model of the DC capacitor voltage variation in this topology is discussed to disclose its balance limitation when the nearest three vector(NTV)synthesis method is employed.Then,HSVM strategy is proposed to extend its balance limitation.In the low modulation rate area,the advantages of the object optimizing method are reserved,which features the good THD performance,low switching frequency and acceptable calculation task.In the high modulation rate area,simplified vector synthesis method can largely reduce the complexity of calculation.HSVM strategy is verified is simulation.3.Experimental platform is designed to further verify HSVM strategy.The modular platform is disclosed from three aspects:structure design,hardware design and software design.HSVM strategy is verified in both high and low modulation area.The advantages of T-type five-level converter in the high power application is clear by comparing with other multi-level converters.The CVB issue is solved by the proposed HSVM strategy,which is validated by both simulation and experiment.