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The emerging utilization of SiC devices in VSDs for motor systems can lead to various advantages, with regards to the operation voltages, switching speeds, operation temperatures, etc. Therefore, compared with the conventional Si device-based VSDs, SiC device-based VSDs would lead to better efficiency and higher power density, which would be beneficial for the success of MEA applications. However, it also introduces new challenges, especially for motor winding insulation. PD behaviors of motor windings under the altered voltage stress are not clearly shown despite the presence of many studies. The impacts of rise time and frequency on PD behaviors have been reported differently in different publications, which is the initial motivation of the work in this dissertation. This dissertation mainly targets the following general challenges related to PD in random wound motors driven by SiC device-based VSDs: the realization of PD detection and measurement under square-wave excitations with ultra-short rise times, quantifications of rise time/pulse width/frequency/pressure impacts without the interference of uncontrolled voltage, and a PD-free design guideline for random wound motor winding.Accurate PD detection of twisted pair samples is realized through co-detection of conventional electrical and optical PD detection methods. The PD pulse currents detected by the former method have been reported to agree with the UV PD signals detected by the latter method very well. Measurement of the PD is realized through subtractions between waveforms captured with commercially available and custom-designed current sensors. The principles of these findings will be beneficial for future PD-related experimental studies.Utilizing the custom-designed pulse generator, square-wave voltage pulses with various parameters and well-controlled overshoot (less than 5%) are utilized to study the impacts of rise time/pulse width/frequency/pressure without the interference of voltage overshoot. A stepwise testing strategy is implemented. The rise time and pulse width impacts are studied under single pulses and quantified through the extended volume-time theory, while the frequency and pressure impacts are studied under repetitive pulses and quantified through curve fitting. The impacts of rise time, frequency, and pressure generally follow the power law, while the impact of pulse width follows the inverse power law. Based on these relationships, PD inception voltages under various conditions could be estimated based on limited experimental data. These findings will be very helpful to motor manufacturers and insulation system designers.The PD-free design guideline for random wound motor winding proposed aims to help motor winding design validation without conducting extensive testing. The guideline combines the PD inception voltage estimation equation described above and Schumann’s equation to acquire the PD inception thresholds Kth for various conditions through FEA simulations. The motor winding design being investigated can then be validated based on its Kt-t value calculated through similar steps. Random wound motor winding insulation designs could then be validated without extensive tests. The proposed guideline will be very beneficial for designers and manufacturers of motor drives and insulation systems to realize PD-free motor systems driven by SiC device-based VSDs suitable for electric aviation applications. |
