Research On Electromagnetic Transient Modelling Of 500kV Unified Power Flow Controller And Simulation Of Faults Overvoltage

Unified power flow controller(UPFC)is the most functional device of flexible AC transmission system(FACTS),which can effectively solve the problem of inhomogeneous distribution of power flow in grid,realize flexible,rapid and accurate control of voltage and power flow,as well as improve the stability and transmission capacity of the power system.At present,the actual engineering cases of UPFC applied power grid are few in our country.Domestic related research is still in early stages,particularly lacking the theoretical and technical support about impacts of the application of UPFC in 500 kV grid.Supported by State Grid science and technology project “Study on control and protect coordination of 500 kV UPFC”,this paper mainly studied the electromagnetic transient modeling and fault and overvoltage analysis of Suzhou South 500 kV UPFC,containing the following:(1)Research on electromagnetic transient modelling of Suzhou south 500 kV power grid and UPFC.According to the power flow calculation data files,this paper built the equivalent model of Suzhou south 500 kV grid and UPFC.The double loop structure control strategy of parallel and series side converters and the circulation current suppression strategy of converter were studied.AC bus voltage/ reactive power injection control and line power flow control for UPFC were implemented.Calculated in PSCAD/EMTDC simulation,short circuit current,steady state performance and dynamic performance of the model could satisfy the fault and overvoltage analysis and calculation.(2)Research on the fault characteristics of UPFC and the influence on the AC system under typical station faults.The single-phase fault on the valve side of the shunt transformer and the series transformer,the DC bus single-pole fault and the inter-pole short circuit fault were theoretically analyzed and verified by simulation.The regulation of overvoltage and zero sequence current in key positions,and the effects on reactive power compensation,line power flow control of UPFC and AC system were obtained.(3)Research on the fault characteristics of UPFC under typical AC system faults.The theoretical analysis and simulation verification of single-phase fault on AC bus,single-phase fault and double-phase grounding fault on AC transmission line were carried out.The values of overvoltage and zero sequence current in key positions of UPFC were obtained.Particularly,because of the special structure of the series transformer,when an AC line fault occurred,the overvoltage on the grid side winding would be much higher than that in normal operation.(4)Preliminary research on the collocation scheme of MOA of 500 kV UPFC.According to the study of the fault characteristics and overvoltage,the protection area and collocation of MOA,as well as the methods and principles insulation coordination of UPFC were studied.The energy and maximum current of each arrester were checked for the single-phase fault on AC transmission line,the single-phase fault of the AC bus and the DC bus inter-pole short circuit fault.The results showed that the energy and current of the MOA on the series transformer windings were large when a single-phase fault occurred on the AC transmission line.Comparison of the overvoltage on the series transformer windings before and after the configuration of the MOA was given.The achievements of this paper could provide a model for Suzhou South 500 kV UPFC and further engineering applications,as well as a theoretically basis for further overvoltage and insulation coordination research and other research projects in the State Grid science and technology project.