Detecting changes of the insulation state of variable speed drive systems based on inverter-built-in current sensors

Modern electrical drive systems basically consist of three components determining its complex impedance system - the inverter, the cabling and the machine itself. For high efficiency and good return on investment these components are operated at or near their rated values. Furthermore stress is added due to high dynamic operation, transient overload and the very fast switching of modern power electronics like IGBT. At the same time more reliability and fail-safety is required by many applications like x-by-wire. This leads to the necessity of continuous drive monitoring that allows the detection of a developing fault in an early stage. The proposed method aims on the detection of an alteration in a component of the drive´s complex impedance system by evaluating the transient reaction of the current on an applied voltage pulse. Such an alteration is e.g. the change of the machine winding´s turn-to-turn or phase-to-ground capacitance due to degradation of the insulation.