Research On Fault Diagonosis And Fault Tolerant Control Of Three-Level Inverter

In recent years, multilevel inverter has been popularly applied in high power fields like aviation, coal, electric power, etc. Among them, three-level inverter, with its advantages like low loss and low harmonic content, has been the focus of both domestic and foreign scholars. Power devices, however, are the most vulnerable parts in the inverter. The failure of power devices could result in economic losses, even system safety problems. Based on Neutral Point Clamped(NPC) three-level inverter, this thesis studies the fault diagnosis and fault tolerant control of power devices, so as to advance the reliability of the system by keeping the system operating after power devices fail.First of all, on the basis of working principle of three-level inverter, the author analyzes the different current paths after different power devices fail in short circuit or open circuit failure. As a result, the position as well as the fault category of the fault device could be achieved by extracting each moment clamp diode current, the arm switch state and load current. Thus, diagnosis logic of three-level inverter based on current path is proposed. Matlab simulation verified the effectiveness of the fault diagnosis method, which can quickly diagnose any switch device’s short circuit or open circuit fault.In order to operate fault tolerant control effectively, the author analyzes the changes of voltage space vector after different faults of different devices. Faults of power devices have been divided into type I, type II and type III due to different characteristics of voltage space vector after fault occurs. The thesis points out that fault tolerant control could be completed by only using the redundant vectors of the inverter after fault. Nevertheless, topology reconfigurantion must be introduced to achieve fault tolerant control after fault type III happens.In view of fault type I and type II, fault tolerant control strategy based on topology reconfiguration is proposed. Sector partition method, vector sequence and then the SVPWM algorithm is specificly achieved. The effectiveness of the fault control strategy is proved by Matlab simulation, so that the inverter could work after fault type I and type II.For fault type III, fault tolerant control method based on topology reconfiguration is put forward. Starting with two level topology configuration fault tolerant inverter as an example, namely three phases four switches inverter, the thesis introduces the basic ideas of topology reconfiguration. Then, three-level inverter configuration topology is given, which means the topology of three-level inverter changes to three phases eight swithes inverter after fault. By analyzing the three phases eight switches inverter’s space vectors, the space vector synthesis method is concluded. Through Matlab simulation, it shows that the fault tolerant control method based on topology reconfiguration can effectively achieve the continuous operation of inverter after fault type III with high reliability and low cost. At this point, the sustainable work of the inverter could be achieved after short circuit or open circuit fault of any power device.