Research On Modeling Of VSC-HVDC Applied For AC System Protection Setting Calculation

As the latest generation of HVDC transmission technology,VSC-HVDC is applied in power grids gradually.However,the fault characteristic of power electronic components based VSC-HVDC,is different with that of conventional facilities.Moreover,its incapability of fault clearance,bring greats challenge to the AC system relay protection.Therefore,the relay protection setting calculation which is the foundation of relay protection that ensures the safety of power grids is required to take VSC-HVDC into account.While the setting calculation system couldn't take VSC-HVDC into account as the absent of equivalent model.It is essential to study the research on modeling of VSC-HVDC applied for AC system relay protection setting calculation.In chapter ?,the basic principle of VSC-HVDC equivalent modeling is proposed.The basic principle of modeling is the fundamental work of this study and related to the equivalent modeling process.Therefore,the fault characteristic of different VSC-HVDC topology is analysis from the perspective of AC system relay protection setting calculation.Then the basic principle of VSC-HVDC equivalent modeling is proposed based on the fault characteristic.The proposed principle provide theoretical guidance basis to the equivalent modeling process.In chapter ?,a method of modeling VSC-HVDC applied for AC system relay protection setting calculation is proposed.Based on the basic principle proposed in section I,analytical expression of DC pole to pole fault and AC system fault are analysis in this section.Then the model applied for AC system relay protection setting calculation is proposed.The proposed method of modeling makes it possible to take VSC-HVDC into account in the AC system relay protection setting calculation.In chapter ?,a novel VSC topology with fault clearance capability is proposed.The proposed topology could reduce the impact on AC system relay protection setting calculation under DC fault condition.In this section,pole to pole fault characteristic of two-level VSC is first analysis,and the topology with fault clearance capability is proposed based on the fault characteristic.Its fault clearance time is within a period of power frequency,a millisecond of rectifier,inverter respectively.Moreover,the fault current is suppressed 50% more and the electric components are shut off with zero-current in the fault clearing process.