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Abstract-A modular power electronic converter, with a cascaded H-bridge multilevel inverter, has been proposed as the grid interface for a large direct drive wind turbine generator. The present study is to investigate the potential and requirement of fault tolerant operation in such a system. As each module is connected to isolated generator coils, tolerance to a module or coil fault is possible if the affected module can be bypassed while the control of the healthy modules can be adjusted accordingly. A boost rectifier scheme on the machine side of the power conversion stage has been developed for this purpose, featuring control of the coil current without measuring the EMF. A coordinated DC-link voltage controller has been developed which can rapidly raise the DC-link voltage of the remaining modules to compensate for the loss of a module, while ignoring the ripple in the DC-link due to low-frequency inverter switching. The ability of the resultant system to tolerate module faults has been demonstrated on a small scale laboratory prototype.

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Multi-chip Insulated Gate Bipolar Transistor (mIGBT) power modules (PMs) degrade over power cycling. Bond wire liftoff is one of the major failure modes. This paper presents a technique to diagnose bond wire lift-off by analyzing the on-state voltages across collector and emitter terminals and the voltages across collector and Kelvin emitter terminals. The proposed method can indicate the first lift-off out of 37 bond wires in a mIGBT. The main novelty of the proposed technique is that it can locate the chip that has bond wire lift-off(s). In addition, the temperature dependence of the proposed approach is negligible. The paper describes the proposed technique in detail and shows results and discussions based on practical tests which are carried out on two mIGBT PMs with different packages. Index Terms-Multi-chip insulated gate bipolar transistor, bond wire lift-off, fault diagnosis.