Design, Modelling and Implementation of High Power Density Drive for Electric Vehicles

Doktorsavhandling, 2023

The world is facing an unprecedented ecological crisis due to our ever increasing demand for energy. Today roughly 37% the total CO2 emissions are generated by transport. In the last decade transportation electrification has seen a large push. This way it is possible to eliminate local emissions and if the electricity generation is CO2 neutral also the global emissions.
Some of the main challenges of  are range and cost. Apart from declining component cost, especially of the battery packs, important factors of the electric vehicle drive-train are efficiency and size. With increased efficiency the cooling system of the drive-train can be smaller and thus the system size and mass can be further decreased. Further drive-train downsizing can be achieved by integrating the inverter and electric motor and utilizing new wide band-gap semiconductors such as SiC. To understand the design process first the vehicle requirements and dynamics need to be understood. Electric vehicle system architecture is therefore first presented in this thesis.
Once the global requirements are taken into account, the inverter design can be performed. Further, an easy to use estimation tool of the inverter losses is required to understand the cooling requirements and feasibility of the design. Therefore, the second part of this work focuses on loss modelling of inverters and semiconductors. Next, the DC link capacitors are discussed and the dimensioning processes are presented.

This work investigates the possibility of utilization of a double-three-phase topology (DTP) to reduce the DC capacitor bank of the inverter. This is achieved by means of carrier wave interleaving which makes it possible to reduce the capacitor current stress. This modulation technique makes it also possible to optimize for the capacitance rating of the capacitor bank. The DTP topology is then utilized when designing a low C-rate inverter for an 800V traction system. The adopted DC link capacitor bank is 23.5 μF. Aluminium substrate printed circuit boards with high thermal dissipation characteristics are investigated as an alternative to SiC power modules. The Al-PCB concept utilizes surface mount devices which are generally cheaper and more available as well as inhibit a higher degree of flexibility for the designer. This makes it possible to mount temperature sensors and current sensors on the Al-PCB increasing the power density further. The flexibility offered by Al-PCB can be exploited to adapt the inverter to the machine geometry for better integration. A prototype with the volume of 2.17 L is then experimentally verified in a prototype capable of delivering 250 kW for a DTP drive.