Study Of Fault Diagnosis And Fault Tolerant Control Of NPC Three-level Inverter

In recent years,Multi-level inverters have been widely used in high-power fields such as aviation,coal mines,and electric power.Three-level inverters are favored by scholars at home and abroad for their advantages of low loss and low harmonic content.However,the power device in the inverter is the weakest link that is most prone to failure.Once the power device fails,the economic losses will cause the system safety.In this paper,the Neutral Point Clamped(NPC)three-level inverter is used as the object to study the fault diagnosis and fault-tolerant control of the power device,so that the system can continue to work after the failure of the power device and improve the reliability of the system.The content of this paper is as follows:Firstly,this paper studies the fault diagnosis of NPC type three-level inverters in detail.Based on the working principle of the three-level inverter,the current flow path before and after the failure of the three-level inverter is analyzed,the clamping diode current,the bridge arm switching state,and the load current at each moment are extracted as the fault characteristics,a three-level inverter fault diagnosis logic based on the current flow path is obtained to accurately locate the faulty power device and diagnose the fault type of the faulty device.The validity of the proposed fault diagnosis method was verified by simulation.Secondly,the fault classification of the power device of the NPC type three-level inverter is connected in order to carry out fault-tolerant control research.In this paper,The different characteristics of the voltage space vector after a short circuit or open circuit fault in power devices at different locations is analyzed,and three-level inverter power device faults are classified into three types:Type I,that is,the short-circuit fault of the outer tube;Type ?,the inner tube Short-circuit faults and external open-circuit faults;type ?,which is an open-circuit fault in the internal switching device.For type I and type? faults,a fault-tolerant control method based on voltage space vector redundancy is proposed,namely a modified SVPWM modulation algorithm,and its fault tolerance performance is evaluated.The validity of the proposed fault-tolerant control method based on voltage space vector redundancy is verified by simulation.Finally,this paper focuses on the Type ? faults of NPC type three-level inverters,and a fault-tolerant control method based on topology reconstruction is proposed.Taking the fault-tolerant topology of three-phase four-switch of two-level inverter as an example,the basic principles of topology-based fault-tolerant control are introduced.Then the fault-tolerant topology of three-level inverter is obtained,the topology reconstruction process is given and the space vector of the new topology is analyzed.Comparing with the space vectors of the three-level inverter normal operating mode,type ? fault and three-phase four-switch topology,the space vector synthesis method is obtained.Finally,the specific SVPWM modulation strategy is given for the particularity of some interval vectors.The effectiveness of the topology-reconstruction fault-tolerant control method is verified by Matlab simulation platform.