Loss Analysis Of Modular Multi-level Converter Based On Half-bridge Sub-Modules

Recently, MMC-HVDC has attracted many attention. Based on half-bridge SM, the method of SM capacitor voltage balancing and circulating current control have been researched systematically, while the analysis of converter valve losses are limited to some particular modes of calculating converter valve total loss rate and the sub-module loss characteristics are lacked of systematical research. On the basis of research of MMC topology, modulation and control methods. This dissertation analyze the sub-module loss characteristics under different control methods.Firstly, MMC operation mechanism is analyzed. By making clear the loss composition of MMC and the calculations method of valve loss, an loss calculation model is built in PLECS, based on which the loss calculation is verified in simulation.Secondly, under NLC modulation the sub-module loss characteristics is analyzed, which include:loss characteristics comparison between voltage balancing method of Limits sorting and voltage balancing method of maintaining factor; loss characteristics comparison of between CCSC and TPD; loss characteristics variation with the variation of capacitance values; loss characteristics of 2N+1 Level number NLC modulation.Thirdly, under CPS-SPWM modulation the sub-module loss characteristics is analyzed, which include:loss characteristics comparison between voltage balancing method of sorting and voltage balancing method of energy balance; loss characteristics comparison of between CCSC and TPD. Besides, loss characteristics with the variation of AC side power factor is also discussed.Finally, temperature characteristics comparison between NLC and CPS-SPWM is discussed.