Research On Fault Diagonosis Strategy Of The Three-Level Inverter

In recent years, multilevel inverters have been widely used in high-voltage and high-power applications, such as grid-connected systems, high-power adjustable-speed motor drives, static VAR compensators, and so on. Among these inverters, the neutral point clamped(NPC) three-level inverters are used most widely in industry. The NPC inverter has the features of less switching loss, higher efficiency; and total harmonic distortion in its ac output voltages are smaller in comparison to those in conventional two-level inverters. However, switching devices are prone to failure in the inverter. Moreover, the number of switching devices in the NPC inverter system is much higher, which increases the probability of fault in the system. In this paper, the fault diagnosis methods of NPC three-level inverter are studied to advance the reliability of the system, thus it has good theoretical research and engineering application value.Firstly, research status of the power converter fault diagnosis is investigated and reviewed detailedly. By analyzing the NPC three-level inverter’s work principle and operating modes, the classification of main circuit IGBT open-circuit fault types is conducted. The faults are classified into typical faults(faults arising from one or two power devices on the same bridge arm) and atypical faults(fault arising from two power devices on two cross bridge arms). The switch open-circuit fault characteristics of three-level inverter are summarized through theoretical analysis and simulation.For the typical faults, the phase current is used as characteristic signal and processed by reconstructive phase space(RPS) method. When the phase current is the same, the bridge voltage is assistantly processed by wavelet packet analysis. So different fault features are obtained to provide data for further fault diagnosis.For the atypical faults, Park transformation is used for three-phase current. Using the reconstructive phase space method, the fault feature vectors of different fault types is obtained and input into multi-class support vector, and the open circuit fault diagnosis of three-level inverter is realized.Finally, in order to recognize the inverter faults, the GUI of three-level inverter’s fault diagnosis system is designed by means of MATLAB/GUIDE based on the methods proposed above. The results improve the observability of the fault diagnosis system.