Power Loss Analysis Of MMC Based On Capacitor Switching Semi-Full Bridge Sub-Module Combining Sic-MOSFET And Si-IGBT

Modular Multilevel Converter(MMC)processes the advantages of good output waveform quality at AC side,high modularity and low loss.Hence,MMC is the preferred converter topology for Voltage Source Converter-High Voltage Direct Current(VSC-HVDC)project.DC fault is one of the key problems of MMC-HVDC.It has good application prospects to rearch the sub-module structure with DC-fault ride through ability.SiC devices has the excellent characteristics,such as,low loss,fast switching frequency and good temperature characteristics.Combining with SiC devices with low power loss and Si devices with low cost,this paper researches the low power loss MMC with DC-fault ride through ability.Firstly,a new type of low-loss MMC sub-module with DC-fault ride through ability,Capacitor Switching-Semi-Full Bridge Sub-Moudle(CS-SFB SM),is proposed.The operation principle and basic characteristics of CS-SFB are analyzed.The low loss characteristics of CS-SFB sub-module are analyzed,including low conduction loss and low switching loss characteristics.Then,this paper proposes the power loss analysis method of CS-SFB MMC system.The loss models of Si-IGBT and SiC-MOSFET are established,and the calculation methods of conduction loss and switching loss of CS-SFB SM are obtained.Combining with the established mathematical model of CS-SFB MMC under normal and boost AC voltage operation condition,the system loss analysis method of CS-SFB is deduced.The conduction losses and basic switching losses of H&FB MMC?CS-H&FB MMC?SFB MMC?CS-SFB MMC under different modulation ratios and power factors are compared and analyzed.The loss of CS-SFB MMC system is the lowest.The power loss of CS-SFB MMC is the lowest.Finally,the CS-SFB MMC loss analysis method is verified by MATLAB/SIMULINK simulation.A three-phase CS-SFB MMC experimental platform is designed and built to verify the low loss characteristics of CS-SFB SM based on current sharing and the fast recovery characteristics of SiC-Diode.