Research On The High Voltage Ride-Through Control Strategy For Doubly Fed Wind Turbines

With the large-scale development of wind power generation,the impact of wind power integration on the reliability and stability of the power grid has attracted much attention.Double fed inverters have a very common application in large-scale wind power generation.Due to their direct coupling relationship with the power grid,when the power system is subjected to a certain degree of interference,it will cause changes in the original state of the power grid,leading to the electromagnetic transient process of double fed wind turbines.Severe disturbances will endanger the safety of the units and even cause unit disconnection.Firstly,the requirements and specifications for high voltage ride through of doubly fed wind turbines at home and abroad were listed,and the basic structure and operating mechanism of doubly fed wind turbines were analyzed.The equivalent circuit and mathematical model of the doubly fed wind turbine in the dq synchronous rotating coordinate system were established.The transient process of the stator flux of the doubly fed wind turbine during high voltage periods,the reactive power of the grid side converter(GSC),and the transient process of the rotor current were analyzed,Solved two main problems during high voltage faults:rotor current overshoot at the moment of voltage surge and rotor current control during sustained high voltage,providing a theoretical basis for constructing high voltage ride through control strategies for rotor side and grid side converters.Secondly,a whole process high voltage ride through control strategy of doubly fed wind turbine based on dynamic adjustment of rotor reactive current is proposed.The PI control module of the current and reactive power components of the grid side converter is designed to maintain the DC voltage stability by using the voltage division of the absorbed reactive current on the incoming inductance;A dynamic adjustment method for rotor current taking into account grid side reactive power was proposed,which controls the stator to provide adaptive reactive power support for the power grid during continuous high voltage periods;A rotor side converter(RSC)transient stator flux differential compensation method is proposed to suppress the transient overcurrent of the rotor during voltage surges.Build a grid connected wind farm model in MATLAB/Simulink,and the simulation results show that the proposed strategy can improve the high voltage ride through capability of DFIG throughout the entire process under different operating conditions.Finally,a low and high voltage cascading fault traversal strategy based on joint control of GSC and RSC was proposed.Control objectives were established and a linear combination of rotor current d,q-axis component and grid side converter current d,qaxis component deviation was selected to form additional variables.The control situation of the model controller was derived,and the selection of controller parameters was explored to damp oscillation and improve the reactive power support capacity of the fan,An AC DC hybrid wind power transmission system was built in MATLAB/Simulink for simulation verification,and the results showed that the proposed strategy can respond quickly to sudden voltage surges in the power grid;Provide reactive power support as much as possible within its capacity range to assist in grid voltage recovery;It can suppress fluctuations in terminal voltage and rotor overcurrent caused by sudden changes in stator flux,achieving low and high voltage ride through operation under different working conditions.