Condition monitoring techniques for multi-chip silicon IGBT modules

Abstract

Multi-chip Insulated Gate Bipolar Transistor (mIGBT) power modules (PMs) are broadly utilised for power system due to their high-voltage and high-current capabilities. However, mIGBT modules are fragile components and therefore prone to failures. For that reason, research focuses on monitoring the conditions of mIGBT PMs aiming to prevent catastrophic failure. Detecting the virtual junction temperature Tvj and bond wire lift-off are the two most common techniques in mIGBT condition monitoring. Thus, this research focuses on the condition monitoring of bond wire lift-off and Tvj. Many techniques have been proposed for Tvj estimation. However, most of the existing techniques are either focused on single chip Insulated Gate Bipolar Transistor (IGBT) module or assuming homogeneous temperature distribution in mIGBTs which is not the case in practical application. Therefore, a comprehensive study was carried out on an mIGBT to investigate the impact of spatial distribution of temperature (SDoT) on existing Tvj estimation techniques. Power converters are subjected to regular maintenance. During maintenance, various parameters of the converter are tested. Detailed health conditions on mIGBT PMs are so far not recorded. This thesis describes a technique to determine the health condition of bond wires when mIGBT PMs are offline. The technique requires a minor modification on mIGBT PMs that allows simultaneous measurement of the on-state voltage across the chips and the terminals of a PM. The proposed technique is able to detect early bond wire lift-offs as well as locate any lifted bond wire. To the author’s knowledge, there has been no work published that addresses the location of lifted bond wires in mIGBT PMs. In general, condition monitoring techniques are influenced by Tvj as well as bond wire condition. Thus, two or more techniques are required to determine both parameters online. In this thesis, a novel technique is proposed to decouple the influence between the bond wire liftoff and Tvj. The proposed technique injects high-frequency and low-power signals to the gateemitter circuitry of an mIGBT PM. The frequency response of the gate-emitter impedance is analysed to determine the root cause. This technique can be embedded in a gate driver circuit and thereby monitor the conditions of mIGBT PMs during the operation of a power converter.