Research On Control Strategy And Fault Diagnosis Of Active Neutral Point Clamped Three-Level Inverter

In the field of medium-high voltage and high power,multi-level is widely used for its advantages of good output performance,small harmonic content,and high efficiency.This dissertation takes ANPC three-level inverter as the research object,and mainly studies its basic working principle,modulation algorithm,switching device loss,open-circuit fault diagnosis method and fault-tolerant control.Based on the topological structure of ANPC three-level inverter,the basic principle of the three-level inverter is studied from the aspects of switching state and commutation analysis,modulation strategy and loss analysis.The switching state and different commutation paths of NPC and ANPC three-level inverters are analyzed.The two traditional modulation algorithms of ANPC three-level inverter SPWM and SVPWM are introduced,and the spectral characteristics are analyzed.A kind of modulation algorithm based on line voltage ab-bc-ca coordinate system is studied.The traditional SVPWM region judgment and vector action time are simplified by coordinate change,and the calculation amount is greatly reduced.The loss of ANPC under three kinds of basic pulse width modulation algorithms is studied,and the loss of NPC and ANPC under the same parameters is further studied.It can be seen that the energy of ANPC three-level inverter greatly improves the unbalanced loss of switching devices in NPC.Defects.This paper focuses on the diagnosis method and fault-tolerant control of an open-circuit fault of a single switching device in an ANPC three-level inverter.By analyzing the commutation path of the open-circuit fault current,the open-circuit fault current characteristics are obtained.For the case of an open-circuit fault in a single switching device,according to the characteristics of open-circuit fault current,two methods of open-circuit fault diagnosis based on the average current Park vector method and three-phase average current method are studied.Simulation results show that both open-circuit fault diagnosis methods can pass the determination rule.Accurately perform open circuit fault diagnosis and locate the location of the faulty pipe.Since both methods need additional sensors to detect and fault features are not easily extracted,this paper presents an open-circuit fault diagnosis method based on instantaneous power.Through the analysis of the fault current derivation,the instantaneous power characteristics of a single switching device under two modulation algorithms are extracted and compared,and the open circuit fault,the fault phase and the device position are discriminated in turn.The fault diagnosis logic and the determination rules are obtained,and the simulation verifies the result.The correctness of the method.The corresponding fault-tolerant control method was studied for the case of an open-circuit fault in a single switching device.After changing the commutation mode,the system can still be in normal operation after a fault.Finally,based on ANPC three-level inverter experimental platform to verify the content of this study,completed the comparison of three-level modulation algorithm,three PWM modulation algorithm,fault diagnosis based on current Park vector,fault diagnosis based on three-phase current average value,Based on experiments of instantaneous power fault diagnosis and fault-tolerant control after open-circuit faults,the experimental results verify the feasibility of the open-circuit fault diagnosis method and fault-tolerant control.