Research On Complex Oscillation Problems Of Large Photovoltaic Grid-connected Systems

In order to deal with the energy crisis and environmental pollution,pv represents the new energy generation as a clean,sustainable energy source that has been widely recognized and developed worldwide.The photovoltaic industry has formed the development of distributed pv and large-scale centralized photovoltaic power station.However,with the increasing capacity of pv grid,the interaction between pv power station and power grid is becoming more and more significant.Based on the large photovoltaic grid system as the research object,according to the stability analysis theory,the interconnected system impedance output impedance model of large photovoltaic grid system is studied,the subsynchronous oscillation mechanism,photovoltaic grid capacity constraints,and stability of the system impedance,and control the grid system based on this,advances the subsynchronous oscillation measures to control the source of the measurement for the development of large-scale photovoltaic power station and the theoretical basis for popularization and application.Detailed research contents is as follow.Using the method of harmonic linearization,the output impedance model of the LCL-type grid-connected inverter is established in the positive and negative sequence.Based on PSCAD/EMTDC,the impedance model was verified by time domain simulation.On the basis of the above model,the impedance parameter characteristics of photovoltaic power generation system are analyzed,and the mechanism of the secondary synchronous oscillation of photovoltaic power generation system is studied.In terms of stability,the constraint conditions of pv power grid capacity are studied.Firstly,the impedance characteristics of the grid-connected photovoltaic inverter are analyzed comprehensively,and the relationship between the grid capacity and the system strength is studied qualitatively.Then,choose a practical system oriented example,from the Angle of the short circuit ratio and weak communication system are analyzed in detail for grid-connected photovoltaic capacity constraints,and in view of the actual system to determine the maximum capacity of photovoltaic power generation system analysis process.Based on the impedance of the interconnect system stability analysis theory,from the Nyquist graph,Byrd chart and time domain simulation analysis of the power grid impedance is pure inductance the stability of the system,inverter at the equilibrium condition is verified the correctness of the grid stability analysis method of system impedance.Then analyzed through source metering power grid inverter supplementary subsynchronous damping controller SSDC suppression principle and related parameters setting method,to verify its validity based on the time-domain simulation method,and the correlation factors affecting the inhibition effect were analyzed.