Analysis of current reaction on inverter-switching to detect changes in electrical machine's high-frequency behavior

Adjustable Speed Drives (ASD) are the favorable choice in a fast increasing scope of applications. Although generally highly reliable, continuous condition monitoring of electrical drive systems becomes more and more important, as the adoption of such systems in safety critical applications, like x-by-wire and in the so called more electric aircraft, increases. To fulfill the demand of high efficiency and good return on investment the different drive components are operated at or near their rated values. This fact and additional stress added due to high dynamic operation, fast switching of modern power electronics like IGBT lead to increased risk of drive breakdown. In many applications this is completely unacceptable and has to be compensated by preventive maintenance, fault tolerant operation or continuous condition monitoring and detection of faults in an early stage. A variable speed drive basically consists of three main components - the inverter, the cabling and the machine itself. These components - including their parasitic elements - form a complex impedance system. The proposed method evaluates the transient current reaction on inverter switching. A change in this reaction is correlated to a change in the mentioned complex impedance system, e.g. resulting from degradation of the insulation system. Application of high-frequency current sampling and further signal processing allow a very accurate monitoring of system parameters and even small changes in magnitude and location can be detected. Experimental results proof the applicability of the proposed condition monitoring technique.