On-board health monitoring of power modules in inverters driving induction motors

This thesis presents an on-board methodology for monitoring the health of power (converter) modules in drive systems. 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 power devices. The novelty of this work is twofold: the complete system that is used to achieve degradation monitoring; combining the heating technique (to obtain thermal transient) and the measurement without additional power components such as IGBT, MOSFETS, which affects the reliability, power density and complexity. The only additional component is an analog measurement circuit, which can be integrated into the gate drive board. The test routine is carried out during non-operational periods and idle times. Trains are used as a case study, where checks for degradation are made when the train is not in use, such as at the end of the day, after daily operation or at the start before daily operation and other non-operational periods. It is important to keep the train at standstill while tests are carried out. Hence a methodology to heat the devices with current from the input supply while keeping the motor load at a stand-still is presented. Experimental results obtained from this show that it is possible to implement an on-board health monitoring system in converters which measures the degradation on power modules. The work uses the concepts of vector control heating and structure function to check for degradation. It puts forward a system that is used on-board to measure the cooling curve and derive the structure function during idle times for maintenance purposes. The structure function is good tool for tracking the magnitude and location of degradation in power modules. Vector control gives the advantage of controlling the motor with field current and torque current (similar concept to DC motors)

On-board health monitoring of power modules in inverters driving induction motors

This thesis presents an on-board methodology for monitoring the health of power (converter) modules in drive systems. 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 power devices. The novelty of this work is twofold: the complete system that is used to achieve degradation monitoring; combining the heating technique (to obtain thermal transient) and the measurement without additional power components such as IGBT, MOSFETS, which affects the reliability, power density and complexity. The only additional component is an analog measurement circuit, which can be integrated into the gate drive board. The test routine is carried out during non-operational periods and idle times. Trains are used as a case study, where checks for degradation are made when the train is not in use, such as at the end of the day, after daily operation or at the start before daily operation and other non-operational periods. It is important to keep the train at standstill while tests are carried out. Hence a methodology to heat the devices with current from the input supply while keeping the motor load at a stand-still is presented. Experimental results obtained from this show that it is possible to implement an on-board health monitoring system in converters which measures the degradation on power modules. The work uses the concepts of vector control heating and structure function to check for degradation. It puts forward a system that is used on-board to measure the cooling curve and derive the structure function during idle times for maintenance purposes. The structure function is good tool for tracking the magnitude and location of degradation in power modules. Vector control gives the advantage of controlling the motor with field current and torque current (similar concept to DC motors)

Evaluation of the Magnetic Field Signature as a Potential Parameter for Power Semiconductor Degradation Detection

This work investigates the viability of using the spatial magnetic flux density distribution caused by a semiconductors load current as a parameter to detect degradation of its bond wires and solder joinings. Utilizing a 3D FEM model of a singular IGBT on DCB, simulations of the B-field distribution for samples with intact and partially interrupted solder layer are conducted. The simulation results show that the partial interruption affects the B-field above the bond wires due to a redistribution of the load current. This is confirmed by measurements of the magnetic flux density distribution conducted on samples with identical structure to the model. Utilizing power cycling tests, 40 additional IGBT samples were artificially aged. The observed degradation mechanisms are bond wire lift-off with varying severity as well as strong vertical solder crack propagation emanating from the chips centre area. Measurements conducted for all aged samples show that the observed type of solder crack pattern has no significant influence on the B-field distribution above the semiconductor. Therefore a detectability using the proposed method can be ruled out. Regarding bond wire lift-offs it is shown that, besides the detection, a localisation as well as an identification is possible. Finally, a method for the determination of the bond wire current distribution is investigated. For this, an analytical model of the spatial magnetic flux density distribution, caused by the current flow in multiple bond wire loops, is derived. Utilizing said model in combination with discrete B-Field measurements, an optimisation approach is presented for the identification and localisation of bond wire lift-offs based on deviations in the estimated current distribution. A first viability analysis shows that the approach is capable to identify and localize bond wire lift-offs within the artificially aged samples