Multi-mode Control Strategy For Dual-stator Brushless Doubly-fed Wind Power Conversion With High Reliability

Brushless double-fed wind generator is a new type of variable-speed constant-frequency machine.When ompared with the traditional double-fed induction generator,this type of motor has eliminated the brush-slip ring structure and inherited the advantages of the slip power conversion.It has the advantages of simple mechanical structure,long service life and low maintenance cost.With the increasing energy crisis and environmental pollution,the search for clean,efficient and alternative clean energy has become a hot topic at home and abroad.Wind power generation has the advantages of low cost,abundant reserves and high energy density,and it is still the most large-scale and commercial development value of new energy power generation.Under this background,brushless doubly-fed generators have become the ideal choice for traditional wind power generation systems because of their unique advantages.They have unique advantages in wind power applications where conditions are harsh,especially offshore wind power generation.In this thesis,a novel double stator brushless doubly-fed induction generator(DS-BDFIG)is considered as the research object.This kind of machine is essentially an integrated cascaded brushless doublefed induction motor.The double stator structure of the motor is conducive to the full use of the motor's radial space,which brings the advantage of compact structure and high power density.At the same time,designing principle of the DS-BDFIG is similar to the traditional doubly-fed induction motor,which enables itself as a very promising wind power generator.To facilitate the theoretical analysis of the control object,the mathematical model o f the DS-BDFIG in the unified coordinate system was established firstly.Then the thesis realized the power winding flux-oriented vector control strategy of the machine in grid-connected condition.With the participation of proper feedforward terms,the control strategy can realize the decoupling control of the active and reactive power through the regulation of control winding d and q axis currents.In order to calculate the reactive power capability of the DS-BDFIG under grid-connected operation,the analytical arithmetic of reative power capability for the DS-BDFIG system is deducted in this theis,which considers the current restraint of the generator and power capacity of the grid side converter together as whole.The thesis designs and implements the control strategy of the independent power generation system based on DS-BDFIG.The power voltage winding unbalanced voltage suppression strategy is then proposed.The compensation strategy is achieved by injecting 2 times the fundamental frequency current into the control winding.The compensation of negative-sequence components of the power winding voltage is beneficial to ensure the power quality of the terminal voltage under nonideal load conditions,such as unbalanced loads,and to improve the adaptability of the independent power generation system based on DS-BDFIG to actual operating conditions.In order to further improve the reliability of the DS-BDFIG wind power generation system,a BDFIG DC grid-connected wind power generation scheme with a single converter is proposed.In the proposed structure,the machine's PW terminal is connected to the DC grid through a three-phase uncontrolled rectifier bridge,and only one voltage source PWM converter is needed to realize the slip power conversion,which greatly reduces the complexity and maintenance of the system.The torque pulsation suppression strategy proposed in this scheme,which is beneficial to reduce the inherent torque ripple of the BDFIG-DC system of a single converter,and can reduce the impact on the wind turbine shafting system while realizing the BDFIG DC grid connection.The experiments are given to verify the correctness of theoretical analysis and proposed schemes.