Research On Dynamic Equivalent Method Of Large-scale Offshore Double-fed Wind Turbine Group

In recent years,offshore wind power has developed rapidly worldwide.As the offshore wind farms scale up and their installed capacity become larger,their impact on the power grid has gradually spread from local to global.During the simulation modeling of large-scale offshore wind farms,the computational complexity will be greatly increased if each wind turbine is modeled in detail,which would lead to long calculation time and may even exceed the node limit of the simulation software.Therefore,the equivalent modeling of large-scale offshore wind farms is a key link to reduce the calculations of simulations.In this paper,the offshore doubly-fed wind farm is taken as the research object,considering the factors that affect the wind speed of wind turbines and the inconsistency of unit parameters in wind farms,a more realistic equivalent model is established to improve its accuracy.The work in this paper is as follows:The structure of the offshore wind farm is analyzed,and a detailed model of a single offshore double-fed wind turbine is established in PSCAD,which including the pneumatic system,transmission system,generator set model,vector control system model and power collection system model.The output curves of the model and the measured data of a wind farm in Yangjiang were compared and analyzed under the conditions of 35%,45%,and 60% voltage drop,respectively.And each voltage drop situation is divided into two kinds of working conditions of high wind and low wind for analysis.The accuracy of the wind turbine model built in this paper was verified.Various factors affecting the wind speed of a wind turbine are analyzed,and a wind speed factor that comprehensively reflects the change in wind speed is proposed to build an equivalent model.The detailed wind farm model,single wind turbine equivalent model and multi-wind turbines equivalent model are built in PSCAD /EMTDC.It is verified that the proposed wind speed factor can simplify the calculation process and reduce the complexity under the premise of ensuring accuracy.The improvement of wind farm density and active output accuracy after considering the wake effect is quantified.Through the analysis of the three-phase and single-phase short circuit fault simulation results of the established models under high wind and low wind conditions,it is shown that the equivalent method based on the wind speed factor is simple and easy to implement.And it also can accurately reflect the power output characteristics of the wind farm.Based on the wind speed factor equivalent method,considering that the clustering of this method is based on the time spot that the clustering results may change with the change of wind speed,and it is not applicable to the different wind turbine parameters in the wind farm,equivalent method based on mixed wind turbine parameters is proposed in this paper.The active output curves of wind turbines are used as a grouping indicator.The geometric template matching method is used to calculate the similarity between output curves.A particle swarm algorithm based on the global best point mutation is proposed after the wind turbines are grouped to identify the key parameters of the equivalent wind turbine,which can reflect the real parameters of the equivalent wind turbine.Finally,detailed models of wind farms,single wind turbine equivalent model and multi-wind turbines equivalent models based on wind speed factor and mixed wind turbine parameters are built in PSCAD,and compared them.Simulation results verify that the proposed mixed wind turbine parameters-based equivalent model has unique and accurate clustering results,which does not change with the change of wind speed,and can well reflect the effect of different wind turbine parameters on the output power of the wind farm.It’s proved that the proposed equivalent model is closer to the detailed model,and the error of the proposed method is verified to be minimal.This paper proposes two dynamic equivalence methods for equating a wind farm with a large number of doubly-fed wind turbines to a few wind turbines,which can greatly improve the accuracy of modeling.The calculation example shows that the error rate of the established equivalence model has dropped by more than 70%.The method proposed in this paper has been applied to Guangdong Power Grid Planning Center.