In-situ health monitoring of power converter modules for preventive maintenance and improved availability

This paper proposes an on-board methodology for monitoring the health of power converter modules in inverters driving inductive loads such as induction motors. The ability to keep regular track of the actual degradation level of the modules enables the adoption of preventive maintenance, reducing or even eliminating altogether the appearance of failures during operation, significantly improving the availability of the equipment. The novelty and originality of the solution proposed here is twofold. First, health monitoring routines are carried out during non-operation phases of the inverter. Secondly, only the circuitry already implemented in the inverter for nominal operation is made use of, without any additional components, apart from an analogue measurement circuit. Degradation is tracked by means of thermal impedance measurements, processed in the form of structure functions for greater resolution and accuracy of information. Vector control is used to supply the heating current from the inverter´s DC source, while making sure that the motor load remains at a standstill. The use of vector control gives the advantage of using the existing control software. Experimental results showing the identification of degradation using structure function and thermal transient measurement extracted from the integration of the inverter and measurement circuit are presented in this work.