Research On Fault-tolerant Control Method Of Converter Power Switches For Permanent Magnet Direct-drive Wind Power System

As the key and core of the permanent magnet direct drive wind power generation system,the failure or function loss of the power converter system will seriously threaten the stable operation and overall safety of the power generation equipment.Research on the fault-tolerant control method of the converter can avoid the system shutdown or secondary fault caused by the converter failure.Meanwhile,it has important practical significance for establishing a high reliable and fault-tolerant wind power generation system.Firstly,the mathematical model of the generator-side converter is analyzed,and its simulation model is built based on Matlab/Simulink.According to the principle of circuit topology equivalence and switches replacement,the fault-tolerant control method of circuit equivalent replacement is introduced,but this method is only suitable for fault-tolerant control of single-switch faults.This paper summarizes four typical open-circuit fault modes,and analyzes the effects of single-switch faults,double-switch faults,and multi-switch faults on vector space sectors.Then,this paper proposes an eight-sector fault-tolerant control method and a twelve-sector fault-tolerant control method by adopting the vector space sector subdivision strategy.Compared with other methods,these methods are more applicable,and twelve sector method can even realize treble-switch fault-tolerant control.By studying vector modulus compensation and vector isometric component compensation,we find that the vector compensation ratio can not be neglected,and its specific value will have a great impact on the fault-tolerant effect.In addition,in order to solve the "spike" distortion phenomenon of three-phase current,four fault-tolerant effect enhancement methods are proposed based on vector space sector subdivision,including sector buffer method,switching frequency method,d-axis current injection method and anti-saturation PI controller method.These enhancement methods have their own characteristics and limitations.Combining them with the eight-sector method or the twelve-sector method can make the faulty converter get better fault-tolerant control effect.Finally,on the basis of theoretical and simulation analysis,this paper designs and builds an experimental platform for generator-side converter,and verifies the new methods one by one.The proposed fault-tolerant control method can effectively improve the three-phase current output sinusoidality and generator rotational speed stability of the faulty generator-side converter.More importantly,it greatly improves the reliability of the converter system.And the fault-tolerant control method proposed in this paper only needs to reconstructthe controller without additional hardware cost,which has the characteristics of strong applicability,high portability and low cost.