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Prognosis of chip-loss failure in high-power IGBT module by self-testing

Reliability is of great importance for power converter systems, such as metro, high-speed train and offshore wind turbine. Bonding wire lift-off is a common failure in IGBT module due to the thermomechanical fatigue under cyclical temperature and power swings. Consequently, this will lead to the chip-loss failure gradually in a high power multi-chip IGBT module during long-term operation. To prevent a catastrophic failure from happening, a self-testing technique for IGBT module is proposed in this paper to detect the chip-loss failure at initial stage. During the test, a shoot-through current is imposed on the device under test (DUT) by gate control and its peak value is selected as the failure criterion for chip-loss failure prognosis. Since the IGBT switching behavior changes after failure, the shoot-through current will deviate from its initial value, which can be detected for failure prognosis. For safety, the self-testing is conducted intermittently on-site during system down time and the shoot-through current is limited less than the IGBT rated current at lowered DC voltage. To clarify the method, its test scheme, working principle and implementation are firstly discussed in the paper. Then, experimental work was carried out on a test rig with 3.3kV/800A IGBT modules (emulating a metro traction drive system) to verify the method. Preliminary test results demonstrate that the proposed self-testing method is a simple and effective technique for detecting the gradually developed IGBT chip-loss failure.