Research On Electromagnetic Transient Modeling Method And Application For Hybrid HVDC Circuit Breaker

A hybrid high voltage DC circuit breaker(DCCB)is an important power electronic equipment for short-circuit fault clearing of flexible DC transmission systems.Large-size complex busbar connection system and large-scale series-parallel basic devices of the hybrid DCCB will bring significant parasitic effects,causing voltage overshoots of key devices such as IGBTs and capacitors during the multiple transient processes of DCCB current breaking.Electromagnetic transient phenomena such as voltage and current oscillations increase the failure risk of devices and affect the reliable operation of the DCCB.The predecessors have not systematically studied the DCCB current breaking's multi-transient process,neither the mechanism research and quantitative analysis of electromagnetic transient phenomena such as voltage overshoot,voltage and current oscillation in the process.Therefore,this dissertation focuses on the electromagnetic transient modeling of hybrid high-voltage DCCB,revealing the effect mechanism of multi-scale,large-scale and complex parasitic parameters on the current breaking transient of hybrid high-voltage DCCB,and laying a foundation for the development of hybrid high voltage DCCB with low cost,high efficiency and short cycle.Firstly,an analysis model for the experimental circuit of a hybrid DC circuit breaker was established,which revealed the influence mechanism of the experimental circuit inductance and the parasitic parameters of the thyristor on the experimental overvoltage,and the effect of the parasitic resistance and the on-state characteristics of semiconductor devices on the experimental circuit current.Furthermore,the experimental overvoltage suppression method and the accurate control method of the experimental circuit current are proposed,and the current breaking experimental platform of the hybrid DC circuit breaker is established,which provides experimental conditions for the subsequent research of various transient models.Secondly,for the internal commutation process of semiconductor submodules inthe DCCB,a partial inductance circuit model and a loop inductance circuit model of a single submodule were established,and the mechanism of the parasitic inductance and the snubber capacitance of the submodule on the transient voltage overshoot of the IGBT device was revealed.The simulated and experimental extraction methods of parasitic inductance parameters in the model were provided and the effectiveness ofthe model and parameter extraction methods were verified through experiments.Furthermore,based on the loop inductance circuit model of a single submodule,an equivalent circuit model for series-connected submodules was established,showing the influence of mutual inductance between various submodules on the overvoltage of IGBT devices.Thirdly,for the commutation process between different branches of the DCCB,an equivalent circuit model of the commutation process of the main branch and the transfer branch was first established,and the parasitic parameters and the influence of the snubber capacitance of the main branch component on the commutation process were introduced.Then,the equivalent circuit model for the commutation between the transfer branch and the energy-absorbing branch was established,and the influence mechanism of the parasitic inductance of the branch busbar and the dynamic characteristics of the metal oxide varistor(MOV)on the overvoltage of the IGBT device was studied.Furthermore,Topologies of the DCCB with discrete MO Vs have been proposed to suppress the overvoltage of IGBT devices.Finally,the equivalent circuit model for the late period of the DCCB breaking was established,and the influence mechanism of the parasitic capacitance effect of IGBT devices and MOV on the voltage and current oscillation was revealed.In addition,the parasitic capacitance extraction method was given and was further verified by experiments.Based on the proposed model of the DCCB,a simulation model of a 200kV flexible DC converter station was built,and the characteristics of the electromagnetic oscillation at the positive and negative ports of the MMC converter valve during the unipolar grounded/bipolar short circuit transient were obtained.