Research On Fault-Tolerant Power Converters And Generation Voltage Ripple Suppression For Switched Reluctance Generators

With the shortage of traditional energy and the intensification of environmental pollution,the utilization of green energy,such as wind energy,is receiving increasing attention.Due to the advantages of simple structure,low price,and outstanding faulttolerant ability,Switched reluctance generator(SRG)have received increasing attention in wind power generation field.In switched reluctance power generation system,the exchange and flow of energy is controlled by power converters,which is an important part of the entire system,and also most vulnerable part.In order to improve the reliability and stability of SRG system,a power converter with fault-tolerant function for the SRG system is proposed in this thesis designs.The fault-tolerant ability and fault diagnosis of the power converter are analysed,and the suppression of voltage ripple in low speed conditions is studied based on the proposed power converter.The main content of the thesis is as follows:Firstly,with the current research status of power converters in SRG systems analyzed,the power converter with fault-tolerant ability is proposed.The structure and working mode of the fault-tolerant power converter is introduced.A comparative analysis of energy consumption is conducted between the proposed fault-tolerant power converters(FT)and the traditional asymmetric half bridge power converters(AHB).The fault-tolerant topology reconstruction method of the fault-tolerant converter in fault situations is also introduced,and the FT power converter is verified that it has the same functions of the AHB power converter and less energy loss through experiments.Secondly,a fault diagnosis method is designed for the fault-tolerant power converters.In order to obtain more fault information,a phase current reconstruction method is proposed: by optimizing the position and winding method of the current sensors,the winding current equations are obtained.Based on the operating characteristics of SRGs,the current information is obtained and bring into the winding current equation to obtain the current value of each phase,and the correctness of the reconstructed current is verified.A fault diagnosis method for fault-tolerant power converters is designed by reconstructed currents.By comparing the consistency of current slope and gate signal,open-circuit and short-circuit faults can be determined.By comparing the relationship between bus current,phase current,and threshold,the fault location can be determined.According to fault characteristic parameters,the fault location and fault type can be determined by controller.The converter is reconstructed by fault-tolerant strategy to maintain the stable operation of the system.The effectiveness of the proposed phase current reconstruction and fault diagnosis method have been verified through simulation and experiments.Finally,the reasons for voltage ripple in SRG power generation system are analyzed,and it is pointed out that the reference current provided by the proportional integral(PI)controller at the target generation voltage is not conducive to reducing voltage ripple.According to the trend of reference current variation and the phase current trend under the current distribution strategy,the reference current output of the PI controller was optimized in two steps.When the phase current increases,voltage hysteresis control is used in the later stage of the commutation interval to slowly release the winding energy and reduce the generation voltage pulsation.The effectiveness and dynamic response effect of the method is verified by simulation and experiments.This thesis has 81 figures,10 tables and 88 references.