Study Of Dynamic Equivalent Modeling Methods Of Wind Farm With DDPMSGs

Large-scale renewable energy integration makes the dynamic characteristics of the system more complex and brings severe challenges to the safe and stable operation of power system.Large-scale wind farms have dozens or even hundreds of wind turbine generators,the capacity of each wind turbine generator is small.In the dynamic analysis or stability study of large-scale wind farm integrated to power grid,if all wind turbine generators in the wind farm are modeled,it will be more complex and more difficult to carry out numerical solution due to the large order of the model.In the current studies on oscillation of weak grid connected wind farm with direct drive permanent magnet synchronous generators(DDPMSGs),single-machine equivalence is generally used for wind farm.On one hand,However,there is a lack of related theoretical support for the single-machine equivalence.On the other hand,compared with the single DDPMSG,the oscillation characteristics of weak grid connected multiple DDPMSGs have begun to attract attention,especially when the parameters of DDPMSGs are different.In the power grid with increasing proportion of wind power,the dynamic equivalence model of wind farm is required to have higher precision in electromechanical dynamic analysis.Therefore,it is of great significance to study the wind farm dynamic equivalent model which has high output precision or preserves all critical eigenvalues(weak damping or negative damping eigenvalues)for the electromechanical dynamic analysis and oscillation research of wind power integrated to power grid.The dynamic equivalent modeling methods of the wind farm with DDPMSGs were mainly studied in this paper,which can be applied to electromechanical dynamic analysis and oscillation research when connected to weak grid.The main work are as follows:(1)A high precision dynamic multi-machine equivalence method for wind farm with DDPMSGs was studied.The dynamic responses of DDPMSG were analyzed and the time series of active power which can reflect the operation characteristics of DDPMSGs was selected as the clustering index instead of single time data.Time delay embedding technology was used for the phase space reconstruction of time series data.The similarity of nonlinear dynamic characteristics among DDPMSGs was mined and measured based on geometric template matching algorithm.The DDPMSGs were clustered by multiway spectral clustering algorithm.The single-machine equivalence was carried out in each gourp.The simulation was carried out based on an example of an actual wind farm.The results show that the output responses of active power and reactive power at point of common connection of wind farm before and after equivalence are consistent,and the proposed equivalence method can be applied to electromechanical dynamic analysis.Compared with the conventional single-machine and multi-machine equivalence methods,the proposed equivalence method has higher precision.When the time series data used for clustering contains a certain amount of noise,the proposed equivalence method still has high precision.(2)A dynamic multi-machine equivalence method for wind farm with DDPMSGs considering the clustering data uncertainty was studied.In the current multi-machine equivalence method of wind farm,the clustering is usually based on deterministic data,and the error of clustering data is not considered.The proposed equivalence method firstly performed multi-scenario sampling based on probability density function of the clustering data.The DDPMSGs were grouped by the probabilistic clustering method based on generalized mixture decomposition algorithmic scheme.The DDPMSGs and collector system were simplified into a single-machine equivalent model in each group.Taking the scene that the clustering index is the wind power prediction data as a simulation example,the output responses were compared among the detailed models,the conventional and the proposed equivalent models in the accurate and inaccurate scenarios of clustering data respectively.The results show that the proposed multi-machine equivalence method still has good accuracy when the data has errors due to the uncertainty of prediction or measurement.(3)Based on analytical analysis and Monte Carlo simulation,the oscillation characteristics and equivalence method of weak grid connected wind farm with DDPMSGs with same parameters are studied.The criterions for the DDPMSGs wind farm to meet the single-machine equivalence were analyzed and presented according to the eigenvalue.Based on the assumption that the parameters,network connection and output of each DDPMSG are identical,the state space model of DDPMSGs wind farm was established.The matrix similarity transformation theory was applied to analytically analyze the eigenvalues and eigenvectors of the state matrix.Based on the criterions,the prerequisites of single-machine equivalence of DDPMSGs wind farm were proposed by comparing with the eigenvalues and eigenvectors of the single-machine equivalent model.Furthermore,under a broader condition than the above assumption,for wind farm with DDPMSGs with same parameters but different network connection and output,the oscillation characteristics of the system and the effectiveness of the commonly used single-machine equivalence method based on parameter aggregation was studied based on Monte Carlo simulation.It provides a certain theoretical support for the application of single-machine equivalent modeling.(4)Based on Monte Carlo simulation,the oscillation characteristics and equivalence methods of weak grid connected wind farm with DDPMSGs with different parameters,network connection and output are studied.The index of coupling degree between DDPMSGs was defined.From three scenarios when DDPMSGs are perfectly coupled,perfectly decoupled and general conditions respectively,based on Monte Carlo method,the oscillation characteristics were studied,including the number of critical eigenvalues,the participation of grid and each DDPMSG to critical eigenvalues and the influencing factors to participation.A single-machine equivalence method for wind farm with DDPMSGs with different parameters,network connection and output was proposed for oscillation research.Based on the admittance characteristics of the wind farm,the least square method was adopted to identify all PI control parameters of the equivalent DDPMSG.The equivalent network parameters were calculated based on constant generalized short-circuit impedance.Simulation results show that the critical eigenvalues are consistent before and after equivalence.The proposed single-machine equivalence method is effective.