Research On Fault Diagnosis Of Converters For Doubly Fed Wind Turbines

With the energy crisis and environmental pollution becoming more and more severe,as a clean new energy,wind power is attracting more and more attention.However,due to the operating environment of wind turbines is relatively poor,coupled with the vulnerability of electronic devices,converter has become the most vulnerable and the highest failure rate component of wind turbine.The wind turbine may be seriously damaged or forced to shut down once any switch failure occurs in the converter,which will affect the reliability and the stability of the system.Therefore,the research on the condition monitoring and fault diagnosis technology of the converter of wind turbines has important significance to improve the reliability and availability of wind power system.In this thesis,firstly,the topology of doubly fed induction wind power generation system is introduced and the mathematical models of the doubly fed induction generator and PWM converter are introduced in detail.Based on that,it introduced a kind of commonly used wind power system control strategy,and the simulation model of the doubly fed wind power generation system is established.Secondly,according to the circuit topology of converter,the running mechanism of converter after open-circuit fault are analyzed in theory,and combining the simulation results under the Matlab/Simulink,concluded that the performances of the variables of the system before and after the converter faults.Then,an open switch fault diagnostic method for converter based on bilinear observer is proposed.The approach is based on mathematical model of the doubly fed induction generator and converter.Combined with the fault diagnosis objective,a bilinear observer is established.So the current residual information is obtained by the current observer,based on that,the fault detection is carried out,and the fault location of the open switch is achieved through the average value of the current.Based on the operating characteristics analysis of the converter fault,combined with adaptive threshold used on the model-based fault diagnostic method,finally,an open switch fault diagnostic approach for converter based on the current vector is proposed in this paper.In this method,the Park's vector modulus-based normalized current average values and the absolute normalized current are obained firstly,then the product of the normalized current average values and absolute normalized current are defined as open switch fault diagnostic variables.Next,according to the Park's vector modulus-based normalized current average absolute values,an adaptive threshold is designed.This guarantees a reliable diagnosis independently of the converter operating conditions.Finally,through the comparision results of diagnosis variables and adaptive threshold,the open switch of the converter are identified.The simulation results indicate that the fault diagnostic method can not only diagnose the multiple open circuit faults of the back to back converter,but also own some better robustness.