Fault Diagnosis And Fault Tolerant Control For The Converter Of Open Winding Brushless Doubly Fed Generator System

In the field of modern wind power,the wind energy resources that can be developed in the offshore wind farm are three times that of the land,and the reserves are very abundant.The offshore wind energy has the advantages of good stability,high wind speed,and easy forecasting.However,the operating environment of offshore wind power systems is extremely harsh,so system reliability is particularly important.For this reason,in recent years,scholars have proposed the concept of fault-tolerant operation of the motor system and received extensive attention.Brushless doubly-fed generators have received extensive attention from researchers because of their brushless structure,lower converter capacity,and flexible operation mode.It improves the reliability of wind power systems from the generator body.The power conversion link,especially the inverter on the machine side,is a fragile link in the wind power system due to its high switching frequency and large energy fluctuations,and is prone to faults.The high reliability of the wind power generation system can be further improved by using the high reliability brushless doubly fed generator,the on-line diagnosis of the fault of the converter and the appropriate fault tolerant control strategy.Therefore,this paper studies the fault diagnosis and fault-tolerant control strategy of the converter in the brushless doubly-fed generator system.The research contents include the following aspects:Taking the brushless double-fed reluctance wind turbine as the research object,the effect of the magnetic field modulation of the reluctance rotor is analyzed,its working principle is outlined,and the vector equation of the brushless double-fed reluctance generator in the stationary coordinate system is deduced.In order to lay a good foundation for studying the control strategy of brushless doubly fed reluctance generator,the vector equation in double rotating coordinate system is further deduced.The no-load simulation model of the brushless double-fed reluctance generator is established under MATLAB/Simulink.The characteristics of the brushless double-fed reluctance generator are simulated and the correctness of the mathematical model is verified.Open circuit of power switches is a common failure in wind power generation system.The open circuit fault diagnosis method of dual two-level converter power switches in open winding brushless doubly fed generator system based on direct power control is studied in this paper.The single phase open circuit fault type of double two-level converter is analyzed in detail.The single phase fault of single converter and the single phase fault of two converters are taken as an example.The phase voltages of the control windings during normal operation and after fault are compared and analyzed to realize fault diagnosis and fault type discrimination.In order to make the system continue to operate stably and meet the performance requirements after the open-circuit fault of the power switch device,the fault-tolerant control of open winding brushless doubly-fed generator is studied.The influence of open circuit fault on output voltage of traditional dual two-level converter is analyzed in detail.In order to improve the fault tolerance of the system,the topology of the converter is reconstructed.Based on the principle of direct power control and the open circuit fault information,the voltage vector switch table is reconstructed.After the failure occurs,the reconfigurable topology of the dual two-level converter is combined with the corresponding voltage vector switch table to make the system run fault-tolerant.The fault tolerant control strategy of open winding brushless doubly-fed generator based on direct power control is simulated and analyzed under MATLAB/Simulink,and the effectiveness of the proposed method is verified.