Research On Wideband Modeling And Transient Characteristics Of Sub-module In Modular Multilevel Converter

VSC-HVDC is the key equipment of strong smart grid.VSC-HVDC has many advantages over normal HVDC,including isolated power supply,city distribution network capacity expansion,interconnetction of AC system,massive wind farm grid connection,etc.Thus it is the strategic choice of our country's mass grid evolution.The most well-known topology of VSC-HVDC is Modular Multilevel Converter,and the key component of which is the MMC sub-module.Thus,the wideband modeling and transient analysis on MMC sub-module is very important.This paper focuses on MMC sub-module in actual engineering.First,the MMC sub-module transient characteristics testing platform is built,which can perform dynamic tests on the sub-module under different voltage,current and switch signals.Then,all the devices inside the MMC sub-module is modeled by detailed circuit model,including analytical model of high voltage IGBT,quick freewheeling diode behavior model,and off-state thyristor model.Meantime,the overall and part stray inductance of the test circuit loop is extracted.Finally,based on the test a nd simulation of two kinds of IGBT modules,the MMC circuit model and parameters extraction method is validated.Also,comparative experiments with and without bypass thyristor are conducted.The influence of bypass thyristor on switch transients is explained and the influence on the sub-module's total loss is analyzed.This paper extracts both the device parameters and the parasitic parameters of MMC sub-module and builds its wideband model.The model has great help on the loss calculation of different operating conditions,the design optimization of sub-module and the electromagnetic disturbance analysis.