The student Leire Elorza Azpiazu obtained an EXCELLENT CUM LAUDE

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The student Leire Elorza Azpiazu obtained an EXCELLENT CUM LAUDE

THESIS

The student Leire Elorza Azpiazu obtained an EXCELLENT CUM LAUDE

2025·10·02

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  • Thesis title: Partial discharge-free electrical machine design for electromobility drives based on wide bandgap semiconductors

Court:

  • Presidency: Andrea Cavallini (University of Bologna)
  • Vocal: Claudia Martis (Technical University of Cluj-Napoca)
  • Secretary: Francisco Javier Poza Lobo (Mondragon Unibertsitatea)

Abstract:

The transition to sustainable mobility has accelerated the development of electric vehicles, with Wide-Bandgap (WBG) converters enabling greater power density and efficiency. However, their fast-switching waveforms increase the risk of Partial Discharges (PD), especially in interturn insulation, posing reliability challenges and reducing insulation lifetime.

This doctoral thesis proposes tools and guidelines to design reliable insulation systems for WBG-based drives, focusing on PD mitigation. The work follows three research lines: (1) PD Inception Voltage (PDIV) estimation under representative conditions, (2) assessment of design and manufacturing factors, and (3) evaluation of insulation endurance under thermal and electrical stress using diagnostic markers.

Novel PDIV models, based on the Extended Dakin’s and parallel-plate, were validated across 140 round and rectangular wire samples under varied conditions, with mean errors of -5.3% and -2.5%. They match the accuracy of simulation-based methods but offer faster results without requiring experimentation. Even if initially developed for interturn insulation, they also proved effective for groundwall systems, notably the Extended Dakin’s model, which requires no parameter fitting.

The influence of manufacturing processes was studied with industrial partners. For instance, several winding techniques and potting application benefits were analysed. PDIV measurements enabled early detection of design weaknesses, supporting robust final design and products.

Ageing tests confirmed that high temperatures and WBG-induced electrical stress reduce insulation endurance. Thermomechanical ageing did not accelerate failure beyond isothermal ageing, indicating that mechanically induced stress does not dominate across all materials. PD-based health markers, PDIV and discharge magnitude, provided the most reliable indicators of insulation degradation and imminent failure.

These results support the integration of insulation modelling and validation into machine development. Future work includes broader model validation, evaluation of interturn insulation across winding techniques, and expansion of ageing datasets, between others.