Research On The Active/Reactive Support Strategy Of Hybrid Wind Farms Under Low Voltage Ride-Through Conditions

With the rapid development of the wind power industry and extensive analysis of the operational performance of various types of wind turbines,a wide range of wind turbine types have been widely applied in the expansion of old wind farms and the construction of large-scale new wind farms.Currently,a hybrid wind farm composed of large and efficient advanced turbines replacing outdated ones has become a global trend in wind power development.In particular,a hybrid wind farm consisting of two mainstream models,namely the doubly fed induction generator and permanent magnet synchronous generator,can utilize the operating characteristics of different types of wind turbines to achieve coordinated control of the units within the wind farm,thereby improving the overall system’s fault ride-through capability.This will become the trend for the future construction of large-capacity wind farms.This article centers on a hybrid wind farm that incorporates doubly-fed and direct-drive wind turbines of varying capacities.It explores the active/reactive power support approach for a hybrid wind farm during low voltage ride-through scenarios,with the aim of amplifying the fault voltage support potential of the hybrid wind farm.Firstly,this paper analyzes the factors affecting the reactive power regulation capability of doubly-fed and direct-drive wind turbines by examining their mathematical models and power relationships.The differences between the factors affecting the turbines under steady-state and fault conditions are compared.The power operation range of wind turbine units under steadystate conditions is transformed into a current operation range more suitable for fault analysis.This provides research basis for investigating the active/reactive power support capability of hybrid wind farms under low voltage ride-through conditions.Secondly,this paper investigates the factors that lead to different operating points of wind turbine units and proposes low voltage ride-through evaluation indicators for hybrid wind farms from both the perspective of wind turbine units and wind farms.Subsequently,by combining the fault current operation range of doubly-fed and direct-drive wind turbines,this paper studies the normalization methods for different wind turbine units in a hybrid wind farm,analyzes the active/reactive power support capability of the hybrid wind farm under low voltage ridethrough conditions,and proposes an optimal current allocation strategy for hybrid wind farms under low voltage ride-through conditions.This strategy can make full use of the remaining capacity of all units to support active power as much as possible during low voltage ridethrough.The proposed optimal current distribution strategy for hybrid wind farms is also validated by building simulation models under different voltage dips.Finally,since the way in which wind turbines are connected in a hybrid wind farm also has an impact on the active/reactive power support capacity,a detailed analysis of the reactive power losses and reactive power compensation equipment in a hybrid wind farm,on the active/reactive power support capacity of the wind farm under low voltage ride-through is presented.To address the problem of difficult reactive power loss calculation in the collector line,a collector line network equivalent calculation method based on the principle of constant line loss is proposed.Based on the optimal current distribution strategy for hybrid wind farms,a secondary distribution strategy for hybrid wind farm current considering internal losses under low voltage ride-through is proposed using the collector line current primary allocation and wind turbine unit current secondary allocation.