Dottorato in INGEGNERIA ELETTRICA, DEI MATERIALI E DELLE
NANOTECNOLOGIE

Titolo della tesi: Design and Development of a 50 kVA GaN-Based Three Phase Voltage Source Inverter For Electric Vehicle Traction

The electrification of the transportation sector plays a vital role in addressing global challenges. As electric vehicles (EVs) become increasingly popular, the need for efficient, compact, and reliable power conversion systems becomes more pressing. This thesis presents the design and development of a 50 kVA gallium nitride (GaN)-based three-phase voltage source inverter (VSI) for electric vehicle applications, with a focus on achieving higher power density, improved efficiency, and reduced size and weight. Through the adoption of innovative design strategies and the integration of widebandgap (WBG) semiconductors, this work contributes to the advancement of power electronics technology for sustainable mobility solutions. A comprehensive design methodology is outlined, beginning with the selection of GaN as the power semiconductor. The design process includes calculating key parameters, such as load requirements, output voltage, and input/output currents. This is followed by determining the optimal number of parallel modules to sustain the 50 kVA power rating, selecting the appropriate DC link capacitor, choosing the driver IC, DC-DC converter, and other essential components. The thermal management strategy, which is critical for high-power applications, is also discussed. A cold plate cooling system is selected based on calculated thermal resistance, with thermal simulations conducted in PLECS confirming that the system maintains junction temperatures of 126°C and case temperatures at 95°C which is well within the safe operating limits of the selected GaN switch model (GS66516B). In addition, a two-stage protection circuit is designed and validated through LTspice simulations, The implemented protection circuit ensures the soft turn-off of power semiconductor within 80ns confirming the effectiveness of protection strategy. The design procedure for the PCBs, including the power, driver, and DC link boards, is thoroughly defined, with a strong emphasis on symmetry and minimizing parasitic elements. This approach ensures optimal performance, enhanced power density, and reduced losses across the system. The thesis also addresses the importance of minimizing parasitic inductances in the power and gate loops, with simulations conducted using ANSYS Q3D Extractor. The optimization process led to a power loop inductance of 3.4 nH and a gate loop inductance of 30 nH (7.5 nH per switch), ensuring efficient operation at high switching frequencies. The system achieves a total efficiency of over 97%, demonstrating the effectiveness of the design in reducing switching losses and improving overall system performance. This research contributes to the ongoing development of high-efficiency, high-power-density inverters for EV applications. The findings from this work demonstrate that GaN-based inverters offer significant improvements in power density, efficiency, and thermal management, which are essential for meeting the increasing demands of the EV industry. The successful integration of GaN technology with effective thermal management and protection strategies paves the way for more efficient, reliable, and compact power electronics systems, and this thesis lays the groundwork for further advancements in this field.