Utilizing the connected power electronic converter for improved condition monitoring of induction motors and claw-pole generators

This thesis first investigates the stator turn-to-turn fault detection for induction motors fed by closed-loop inverter drives. A comprehensive survey of existing stator turn-fault detectors reveals that the major disadvantage of conventional methods is that the process of learning the inherent asymmetry of the induction motor is highly complicated. Such complexity directly limits the practicability of these methods in real world applications. In this work, it is discovered that motor current controllers in the closed-loop inverter can keep the three-phase current symmetrical no matter a stator turn fault exists or not. This unique feature is utilized to essentially eliminate the learning process of the motor inherent asymmetry during stator turn-fault detection. The proposed method is evaluated experimentally and the results show that the proposed fault detector is highly sensitive and easy to implement.;In addition to detecting a solid stator turn fault, an early warning of the stator insulation degradation is also highly desired. A stator thermal monitoring method is thus proposed in this work to protect the closed-loop inverter-fed induction motor from insulation degradation caused by thermal overload. The stator temperature is indirectly estimated from the stator resistance. The closed-loop inverter is used to inject a DC current into the motor windings in an online fashion. Since only the DC bus voltage sensor is available in typical closed-loop inverter drives, the major challenge of this method is how to accurately estimate the DC component of the motor terminal voltage despite inverter nonidealities. The proposed method is finally implemented in real time in a custom-built programmable inverter drive. The experimental results demonstrate that the method gives accurate and robust stator temperature estimation regardless the operating condition of the induction motor.;The health monitoring of claw-pole generators with built-in rectifiers is also studied in this thesis. Despite the limited literatures on the major failure modes of claw-pole generators, several common types of faults are successfully identified and studied in detail. Different from grid-connected AC generators, the built-in rectifier of the claw-pole generator makes it difficult to access the three-phase voltage and current measurements. Hence, conventional condition monitoring methods based on AC signals can no longer be used. To overcome this challenge, an experimental analysis is performed to better understand the overall waveforms and spectra of the voltage and current of the claw-pole generator. Several harmonic components in the output current spectrum are identified to be related to various faults of the claw-pole generator.;Faults of claw-pole generators are classified into two categories: External faults (or system-related faults) and internal faults. Specifically, the external faults of claw-pole generators studied in this thesis include the serpentine belt slip and serpentine belt defect. For the serpentine belt slip, the speed of the claw-pole generator is estimated indirectly by tracking the rectifier ripple frequency in the output voltage signal. Hence, the fault is reliably detected by comparing the estimated generator speed with the measured speed of the prime mover (vehicle engine). The defects on the serpentine belt, on the other hand, modulate the transmitted torque and speed of the claw-pole generator every belt cycle. It is therefore detected by monitoring some specific side-band current harmonics near the rectifier ripple frequency.;The internal faults of claw-pole generators studied in this thesis include the stator turn-to-turn fault, the rotor eccentricity, and the worn bearing. It is discovered that with unbalanced three-phase inputs, the output current of the rectifier will exhibit increased harmonic at one third of the rectifier ripple frequency. This signature is used to detect stator turn faults. Once the stator turn fault is detected, an analytical model of the claw-pole generator with fault is also derived to establish an accurate mapping relationship between the observed fault signature and the fault severity. The experimentally validated model enables the design of well-informed post-fault protection strategies, which prevent the stator turn fault from progressing into catastrophic generator failures while maintaining maximum limp-home capability of the vehicle. (Abstract shortened by UMI.)...