Fault Diagnostic System for Cascaded H-Bridge Multilevel Inverter ...

2.3 Fault diagnosis in an inverter of a CID system
A CID system usually consists of three cascaded subsystems: a rectifier, an inverter, and
a motor. A review of fault detection techniques in an inverter is focused in this section.
As previously mentioned, input motor supply current signals could be used to detect
switch base drive open circuit and inverter switch short circuit fault. Two techniques are
primarily applied in fault detection and diagnosis: model based technique and model-less
based technique.
A model-based technique principally depends upon a mathematical model; for instance,
analytical redundancy method and parameter estimation method. A model based
technique is valuable if an accurate model of faults can be obtained. However, in the case
of a CID, an accurate model representing all of the possible fault cases is difficult to
obtain. A model based technique has some disadvantages as follows:
• expensive in engineering time to develop model;
• model may not be robust to nonlinear problems;
• model may not be robust to seasonal changes or plant degradation.
A model-less based technique is based upon expert-knowledge or artificial intelligent
system; namely, a fuzzy logic, a neural network, and a statistical technique. An
implementation of a model-less technique may be more expensive than a model based
technique; however, the technology promise of very large scale integration (VLSI)
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