Research On Improved Control Of Fault Ride Through Of Doubly-fed Wind Turbine

With the rapid development stage of new energy,especially the continuous increase of grid-connected capacity of wind power,whether the Doubly-Fed Induction Generator(DFIG)is faulty in response to the sudden disturbance of the grid during operation in recent years.The ability to traverse is the key and difficult problem of current research.At present,DFIG’s low voltage ride-through technology is relatively mature,and the research on the high voltage ride-through(HVRT)problem of doubly-fed wind turbines has not attracted enough attention.Therefore,it is of great significance to study DFIG’s improved Fault Ride Through control scheme.Aiming at the HVRT problem of doublyfed wind turbines,the main research work of this paper is as follows:(1)The structure and working principle of the doubly-fed wind turbine are analyzed in detail,the mathematical model of DFIG in the two-phase static coordinate system is established,and the mathematical model of the grid-side converter(GSC)in the two-phase rotating d-q coordinate system is analyzed.The steady-state voltage equation of the DC bus based on the GSC control is derived,and the maximum withstand voltage limit expression of the DC bus voltage is obtained based on the analysis.Aiming at the problem that the DC bus voltage rises due to the swelling of the grid voltage DFIG high voltage ride through control scheme of Chopper unloading circuit.(2)The transient process of stator flux and rotor current of DFIG is analyzed in detail,the expressions of stator voltage and rotor current are deduced,and the value of current-limiting resistance is set and analyzed.Aiming at the problem that the Chopper circuit control method is insufficient in suppressing the current fluctuation on the rotor side,an improved DFIG high voltage ride-through control scheme based on the rotor string resistance is proposed.(3)Based on the improved control of the Chopper unloading circuit and the rotorside series resistance,this paper proposes an improved HVRT control scheme for doubly-fed wind turbines based on supercapacitors,deduces the configuration range of the supercapacitor capacity,designs and analyzes the bidirectional DC /DC converter controls the charging and discharging of super capacitors to realize the principle of DC side voltage control.Demonstration and analysis of the advantages of the three control schemes from the perspective of the improvement effect on the DC bus voltage,rotor side current and stator voltage and the total reactive power absorbed by the unit.