Research On The Influence Of The Aggregated Equivalent Of The Direct-driven Wind Farm On The Characteristics Of The Subsynchronous Oscillation Of Grid-connected System

In recent years,subsynchronous oscillation accidents caused by large-scale wind farm have occurred both at home and abroad,seriously threatening the safe and stable operation of a high proportion of new energy power systems.In order to reduce the order of the model and improve the computational efficiency when studying the subsynchronous oscillations caused by the grid connection of wind farms,aggregation equivalence is usually performed for wind farms;However,whether the wind farm equivalent model can accurately retain the subsynchronous modal characteristics of the original system,and how factors such as control parameters,power collection lines,and operating points in the wind farm affect the subsynchronous oscillation characteristics of the equivalent model,all of which require a quantitative evaluation of the fidelity of the subsynchronous modal characteristics before and after the wind farm equivalent.Therefore,this paper quantitatively evaluates the similarity between the equivalent model and the detailed model in terms of subsynchronous oscillation characteristics to study the impact of the aggregated equivalent of direct-driven wind farms on the subsynchronous oscillation characteristics of grid connected systems,thereby providing a reference basis for the aggregated equivalent method for analyzing wind farms in subsynchronous oscillation.Firstly,a full order small signal model of direct drive wind turbines is established,including wind turbines,generators,converters,and control systems;On this basis,small signal models for a single direct drive wind farm and small signal models for wind farm stations including multiple direct drive wind farms are established respectively;The capacity weighting method is used to aggregate the two models to obtain the internal aggregation model of a single direct drive wind farm and the inter station aggregation model of multiple direct drive wind farms,respectively;The accuracy of the small signal model is verified through the electromagnetic transient simulation of PSCAD/EMTDC.Aiming at the internal aggregation equivalence of a single direct drive wind farm,considering the differences in wind speed within the wind farm caused by wake effects and the differences in control parameters of different link wind turbines,key oscillation characteristics of the system before and after the equivalence are extracted,including subsynchronous modal frequency and damping ratio;A combination of numerical similarity and trend similarity was used to quantitatively evaluate the impact of aggregation equivalence within wind farms on the fidelity of subsynchronous modal frequencies and damping ratios.The results show that the wind power difference has a small impact on the subsynchronous oscillation characteristics of the equivalent model;The influence of control parameter differences on the oscillation characteristics of the equivalent model is higher than that of wind power,with the outer loop proportional coefficient having a greater impact;When the control parameters differ significantly,it may lead to a problem of inconsistent subsynchronous oscillations before and after polymerization.Aiming at the problem of equivalent modeling for wind farm stations with multiple direct-driven wind farms,considering the differences in wind speed,control parameters,and outlet line lengths of different wind farms and substations caused by spatial distribution,the impact of aggregated equivalence between stations on the fidelity of subsynchronous modal frequencies and damping ratios was also quantitatively evaluated using a combination of numerical similarity and trend similarity.The results show that the influence of wind power and control parameter differences on sub synchronous modal characteristics is similar to that of a single wind farm,but the influence of aggregation equivalence between stations on sub synchronous modal characteristics is greater than that of aggregation equivalence within a wind farm;When there is a difference in the length of the wind farm outlet line,the impact on the subsynchronous modal characteristics is greater than that of the substation outlet line.