Research On Variable Speed Constant Frequency Brushless Doubly Fed Generator Control System

For wind power generation,wind energy is a clean energy with the characteristics of renewability and instability.In order to meet the increasing requirements of grid connection specifications,doubly fed variable speed constant frequency power generation technology has become a research hotspot in the field of wind power generation.Brushless doubly fed generator cancels the structure of brush and slip ring,which not only overcomes the shortcomings of easy damage of brush slip ring and high maintenance cost of traditional brush doubly fed generator,but also inherits the advantages of small requirements for frequency converter capacity and variable speed and constant frequency operation.It can operate in various modes and has very important application value in the field of wind power generation.The rapid development of wind power also puts forward higher requirements for the performance and safety of brushless doubly fed power generation system.However,the present research on parameter identification of brushless doubly fed generator is not deep enough,which has become an obstacle to its popularization and application.The main research contents are summarized as follows:1.The operation principle of brushless doubly fed generator is analyzed,and the theoretical basis of variable speed constant frequency operation is obtained.The energy transformation relationship between windings of the generator under different operating conditions is analyzed.The vector control strategy is designed based on the mathematical model of the generator in the two-phase rotating coordinate system.On this basis,the performance of the control system is discussed,including the analysis and comparison of the stability of different vector oriented control systems and the analysis of the dynamic response capability of the control system.In this dissertation,the process of generator grid connection is analyzed,and a phase controller is designed to improve the process.2.The coupling disturbance caused by the rotating electromotive force in the vector control strategy affects the output power decoupling and the dynamic performance of the system.In this dissertation,the feedforward control is introduced to eliminate the coupling disturbance.The relationship between the accuracy of feedforward parameters and the coupling disturbance and the dynamic performance of the control system is discussed.It shows that the design of appropriate feedforward parameters highly depends on the motor parameters.Based on the characteristics of control model and decoupling control conditions of power generation system,a method for identifying integrated coupling parameters using closed-loop transfer function is proposed.This method only focuses on the parameters needed for control,bypassing the identification of specific parameters of the motor.3.Power grid voltage fault will impact the voltage and current of generator stator and rotor.In order to enhance the ride through ability of brushless doubly fed generation system during power grid fault,the corresponding control strategy is designed by analyzing the mathematical model and transient process of the generator under fault conditions.For the voltage symmetry fault,the virtual resistance control is used to suppress the oscillation of the voltage and current transient response of the control winding.For the asymmetry voltage fault,the dual synchronous rotating coordinate system and virtual resistor are used to improve the control performance.4.Set up an experimental platform for brushless doubly fed generator power generation system to verify the variable speed constant frequency power generation operation,soft grid connection control and active power and reactive power decoupling control of brushless doubly fed power generation system;The proposed parameter identification method is tested to verify its accuracy;The fault ride through experiment is carried out to verify that the brushless doubly fed generator can ride through the symmetrical fault and asymmetrical fault without crowbar circuit.