Efficiency Comparison between Two-Level and T-Type Inverter for 800 V Automotive Application

Abstract: The falling cost of batteries, along with an increasing need to cut emissions, has spurred significant interest in the electrification of vehicles. In addition, as semiconductor devices have evolved, the research for electric vehicles with higher battery voltage has increased. The traction inverter is an important part of the electric power train and can account for a substantial portion of the drive train’s losses. This thesis therefore models, simulates, and studies the losses for a convectional Two-Level (2L) inverter and a Three-Level T-Type (3LT) inverter utilizing Silicon Carbide (SiC) MOSFETs and compares the two inverter topologies in terms of efficiency. The rated power of the inverters is 120 kW at a DC voltage of 800 V. The theoretical basis of SiC MOSFET and its reverse conduction, operation of 2L and 3LT inverter topologies, and Space Vector Pulse Width Modulation (SVPWM) technique are introduced in the initial part of the thesis. To estimate switching and conduction losses, Simulink is used to model and simulate an electric drive system. These estimated losses are then utilized to develop efficiency maps for both topologies over the complete speed-torque range. Based on the efficiency comparison, the 3LT topology outperforms the 2L topology for any requested torque in the medium to the high-speed range, which is typical of highway driving. In the low-speed, high-torque region, which is typical of city driving, the 2L topology is superior. The efficiency of each topology is affected by switching frequency, device junction temperature, and DC-link voltage. However, the comparison reveals that the maximum average difference in efficiency is 0.35%, with the 3LT topology being superior. Finally, the efficiency differences between the two inverter topologies are minimal. As a result, it may be concluded that the two topologies perform similarly. Thus, it can be inferred that comparing the efficiency of the two topologies should not be the sole criterion for selecting which topology should be used for the electric drive.