Research On Electrical Stress And Parameter Configuration Of Key Components Of Hybrid DC Circuit Breaker

The high-voltage DC circuit breaker is the core equipment to ensure the safety of the DC power grid.Improving the fault current breaking capacity is a technical problem that must be overcome.Hybrid high-voltage DC circuit breakers combine the good static characteristics of mechanical switches and the good dynamic characteristics of power electronic devices,and become the mainstream research direction of DC circuit breakers.Hybrid high-voltage DC circuit breaker is a new type of high-end equipment.Its commutation characteristics and breaking capacity directly determine whether the circuit breaker can work reliably.Therefore,the millisecond-level breaking process of the DC circuit breaker and the microsecond commutation process are studied.The electrical stress of the relevant components is a key issue that must be recognized and resolved during the electrical design of the circuit breaker.This thesis focuses on the electrical stress and parameter configuration methods of key components of hybrid DC circuit breaker.In this thesis,the 500kV hybrid high-voltage DC circuit breaker for Zhangbei project is taken as the research object.Firstly,its topology structure and working principle are analyzed.On this basis,the electrical stress of the whole machine and the transient electrical stress of the key components in two commutation processes are studied in detail.In order to facilitate analysis and elaboration,the two commutation processes are divided into four stages,and the equivalent circuit corresponding to each stage is given.According to the equivalent circuit the mathematical model of the transient electrical stress experienced by each component is obtained.Secondly,a refined simulation model of hybrid DC circuit breaker is established.The calculation of the stray inductance of the semiconductor sub-module and the establishment of the MOV model are briefly described,and the focus of the modeling is IGBT model.According to the shutdown characteristics of IGBT under the specific application conditions of hybrid DC circuit breaker,a functional model of IGBT under high current shutdown condition is proposed to mathematically model the IGBT turn-off transient process.In addition,Completing the model build in PSCAD.At the same time,the diode-full bridge sub-module breaking test platform is built.The test results show that the breaking test waveforms and simulation waveforms at different current levels agree well,which proves the correctness and effectiveness of the IGBT functional model.Finally,the refinement model of the hybrid DC circuit breaker is used to simulate the influencing factors of the relevant stresses in the whole process of the circuit breaker and the two commutation processes,and the influence of various influencing factors on the commutation time and the electrical stress of key components is obtained.According to the influence rule and the actual engineering requirements,the parameter configuration methods of the key components such as capacitors and MOVs in the main branch,transfer branch and energy absorption branch are given.