Circulating Current Analysis And Control Of Rectifier In Permanent Magnet Direct Drive Wind Power System

With the increase of the single machine capacity of the wind power system,more and more energy needs to be transmitted to the grid.However,due to the limited capacity of power electronic devices in the wind power system,in order to improve the reliability and stability of the operation of the wind power system,it is necessary to parallelize the converters in the wind power system,but the parallel operation of the converters will inevitably lead to the circulation of the system.For this reason,this paper takes the rectifier in the permanent magnet direct drive wind power system as the research object,and completes the following work:1、The development status of wind power industry at home and abroad and the current types of wind power generation systems are described,the research status of rectifier control technology is analyzed,and the research status of parallel connection technology and circulating current suppression technology is summarized.2、The structure and operation principle of wind power system are introduced.The mathematical modeling of wind turbine generator,DC link and generator side rectifier is carried out.The control strategy of wind turbine generator and the double closed loop control strategy of generator side rectifier are analyzed.The calculation process of parameters of current loop and voltage loop in the double closed loop control strategy is derived in detail.3、Firstly,based on the simplest practical voltage source model,the definition of circulating current is described simply and easily;Secondly,based on the structure of parallel rectifier,the cause of circulating current of parallel rectifier is introduced;Finally,the circulating current of parallel rectifier is modeled in detail in three-phase stationary coordinate system and synchronous rotating coordinate system respectively.4、In order to solve the circulating current problem of parallel rectifier structure,the existing minimum beat algorithm circulating current control strategy based on zero vector distribution method is introduced,and the zero vector distribution method and the principle of this control strategy are introduced;Then,based on the zero vector assignment method,a new feedforward and feedback loop control strategy is proposed,and its stability and controller parameters are proved and derived in detail;Finally,through Matlab/Simulink simulation software,the minimum beat algorithm circulation control strategy and the new feedforward and feedback circulation control strategy are compared and analyzed.The results verify the effectiveness of the new feedforward and feedback circulation control strategy proposed in this paper.5、Considering the influence of traditional voltage loop on the restraining effect of circulating current and the disturbance in the mathematical model of circulating current,a new voltage loop structure based on ant colony algorithm and single neuron voltage loop is designed to cooperate with the linear active disturbance rejection circulating current control strategy.Firstly,the basic principle of LADRC is introduced,and the basic principle of circulation control strategy based on LADRC is expounded;Then,based on the neural algorithm and PI control theory,a single neuron voltage loop structure is designed.Because the gain coefficient of the controller in the single neuron voltage loop is required to be optimal,considering the characteristics of the ant colony algorithm,the ant colony algorithm is introduced into the single neuron voltage loop to form a new voltage loop structure;Finally,through Matlab/Simulink simulation software,the traditional voltage loop and the new voltage loop are compared and analyzed with the linear active disturbance rejection loop control strategy respectively.The results verify the effectiveness of the new voltage loop designed in this paper.