Research On The Control Strategies Of Wind Power Generation Based On Doubly-fed Induction Generator And Its Fault Ride Through Technologies

Wind energy is renewable and clean.Wind power generation is an important form of wind energy utilization.In Variable Speed Constant Frequency(VSCF)wind power generation technology based on Doubly-Fed Induction Generator(DFIG),the speed of generator can timely follow the changes of wind speed,and the control system can ensure that the output frequency of generator remains constant.The control strategies of PWM converter in DFIG's AC excitation power supply was studied in depth.When the grid voltage drop occurs,the Fault Ride Through(FRT)methods of auxiliary hardware devices and improved software control strategies was proposed to help VSCF DFIG wind power generation system to meet the power rules requirements.The main work and innovative contributions of this paper are as follows.(1)The flux equation,voltage equation,motion equation and torque equation of DFIG in three-phase static coordinate system and two-phase synchronous rotating coordinate system were established respectively.The vector control method oriented on stator voltage vector was adopted to achieve independent control of direct-axis component and cross-axis component in the DFIG rotor excitation current,and to attain decoupling control active and reactive power.(2)The mathematical model of PWM converter based on bidirectional energy flowing was established.The vector sequence optimization method based on PWM converter AC side voltage angular position was proposed.The calculation method of each voltage vector duration time in deadbeat predictive direct power control method was given in this paper.(3)The Proportion Integration Resonance(PIR)control method could be applied to PWM converter in asymmetric grid voltage.The quasi PR controller and the influence of controller parameter setting to bandwidth and output peak gain were discussed.The PIR control algorithm can effectively control the voltage in resonance point,can effectively reduce the 2nd ripple in PWM converter DC voltage.(4)When the voltage fault occurred in the power grid,the active Crowbar protectioncircuit was used to help VCSF DFIG wind power generation system to achieve FRT.The resistance of Crowbar resistor was determined according to relationship between it and the maximum peak voltage of rotor current and rotor voltage as grid voltage dropping.The input and removal control method of Crowbar protection circuit was proposed.Chopper protection circuit was applied to limit the overvoltage of DC capacitor in AC excitation power supply.(5)The novel FRT technology based on variable damper was proposed in VSCF DFIG wind power generation system.The relationship between the virtual variable resistance and the fault grid voltage was studied.The effective control of excitation current and VSCF DFIG wind power generation system FRT were achieved in FRT technology based on variable damper.(6)The experimental platform of VSCF DFIG wind power generation system was developed.The control methods of PWM converter proposed and the FRT methods of VSCF DFIG wind power generation system proposed in this paper were verified in the experiment system.In grid voltage symmetry situation,the vector sequence optimization method based on PWM converter AC side voltage angular position to divide sectors could reduce the harmonic content of the PWM converter output current.The control method of Crowbar +Chopper protection circuit and the method based on variable damper proposed could control excitation current in DFIG,could improve FRT capability of VSCF DFIG wind power generation system.