Methods for assessing the impact of silicon carbide traction inverters in electric vehicles

The automotive industry is witnessing a shift toward large-scale production of Electric Vehicles (EVs) characterized by higher voltage levels, deeper integration of High-Voltage (HV) components, and more complex and flexible HV Direct Current (DC) bus designs. Emerging semiconductor technologies, such as Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), hold promise for increased efficiency and extended range. To ensure the safe and reliable operation of these systems, it is necessary to consider the current harmonics generated by the traction inverter and their distribution within the HV DC system, as these harmonics can affect the safe operation of the system. This study aims to provide insights to improve the performance, efficiency and reliability of future electric mobility. The efficiency and range of EVs are strongly influenced by its driving cycle, which determines the operating points of the traction inverter. These operating points, in turn, have a significant effect on the current harmonics generated by the traction inverter. Their distribution on the DC bus depends on the output impedance of the traction inverter and the DC bus impedance. In this research, impedance measurements of HV components are used to develop equivalent circuit models along with time and frequency domain simulation models. These models are validated using a laboratory DC bus setup. The dissertation investigates the influence of DC bus modifications, such as the addition or modification of HV components, and proposes a method to model and analyze the distribution of current harmonics across the DC bus and its HV components. Furthermore, this thesis performs a detailed calculation of semiconductor losses during the driving cycle of an EV traction inverter, considering different semiconductor materials and a wide range of influencing parameters. An open source tool is developed to facilitate these calculations, covering aspects from driving resistance to inverter loss calculations. Static and dynamic losses derived from experimental tests are compared with data sheet values and calculation results. The advantages of SiC MOSFETs over Silicon (Si) Insulated-Gate Bipolar Transistors (IGBTs) are analyzed, revealing higher performance advantages for driving cycles with a high proportion of partial load operating points. However, the advantage over Si IGBT is less pronounced for high power operating points or demanding driving cycles. Real EV measurements are used to evaluate the current ripple during steady-state operating points in both time and frequency domains. In addition, a method is proposed to extract the EV velocity using short-time Fourier transform based on the DC harmonics of transient operating points. The thesis examines the effect of DC bus impedance on the DC current spectrum of the traction inverter and its distribution within the HV DC bus of the EV. A method is proposed to transfer current measurements from standardized laboratory setups to the more complex DC bus configurations found in typical EVs. In addition, the critical frequency components of the traction inverter for the complex DC bus are discussed. In conclusion, this dissertation analyzes the advantages of SiC MOSFET traction inverters and discusses their influence on the DC bus in EVs.

Author dc:creator

• Schlüter, Michael Alfons

Advisor dc:contributor.advisor

• Dieckerhoff, Sibylle

Licence dc:rights.uri

• https://creativecommons.org/licenses/by-nc-sa/4.0/

Language dc:language.iso

en

Identifier URI

https://doi.org/10.14279/depositonce-22315

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/23501