Study On Reliability Model Of IGBT

Utilization of wind power is one of the key measures to solve energy and environment problems. Actually, application of wind power is limited by grid-connected inverters'reliability, which is usually caused by the degradation of power devices due to the inherent power fluctuation of wind power. So, reliability assessment of power devices is prior to that of grid-connected inverters. However, seldom works have been done to investigate the mechanism of power devices performance deterioration, leading to the deficiency of degradation knowledge and fault feature. On the other hand, off-line reliability assessment of power devices and grid-connected inverters is also restricted since there is little reliability index (such as average lifetime, availability, aging failure rate, unavailability) for power devices. Consequently, this paper dealed with the on-line state monitoring and probability assessment of IGBT, and the concrete works are as follow:①Temperature characteristics of IGBT physical parameters were derived, according to which, mechanisms of switch speed slowing, on-state voltage drop and leakage current deterioration, threshold voltage mutation, and the latch-up effect were analyzed to establish the corresponding relationship between the physical and electrical parameters of IGBT. The above work laid a foundation for the IGBT's aging mechanism and dynamic model analysis.②A lumped-parameter circuit model was presented and created in PSPICE simulator to represent the dynamic characteristics of IGBT, in which parasitic capacitances were represented with diode model. The model parameters were extracted with IGBT datasheet as well as laboratory measurement. Measurements confirmed the accuracy of the presented model. Sensitivity study of model parameters determined the dominant parameters that significantly affect the dynamic characteristics of IGBT.③Theoretical analysis of the dynamic characteristics of IGBT was carried out to define the three-phase characteristics of gate voltage. A 2MBI150U4H-170 IGBT without packaging was used to simulate and comparatively analyze the dynamic characteristics before and after wire-bond lift-off. Results revealed that, Miller plateau can be considered as a reference signal under fault free condition. At last, an on-line reliability model for IGBT was developed based on the comparison of the gate voltages in fault free and faulty condition. ④A method to estimate the mean life, probability and unavailability of IGBT aging failure with limited aging failure data was presented to improve the reliability assessment for design stage. The method was based on the normal distribution model, and its parameters were obtained by least square method. Unlike the conventional sample mean technique which only uses ages of died components, the method mentioned above was based on all the information in an IGBT group including both died and surviving components and provided a more accurate estimation.This paper dealed with the PSPICE dynamic model, the on-line and off-line reliability assessment of IGBT, which were valuable for investigating the reliability of grid-connected inverters and their lifetime.