Modelling and design of a GaN based motor drive for the Nuna solar car
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Abstract
In recent years, electrical vehicle (EV) starts showing its unique advantages that the conventional combustion vehicles do not have. Together with the increasing interests on EV, the motor drive with higher efficiency and lighter weight also becomes more attractive. To reduce the time and cost for the development, the project is aiming for the modelling of the motor drive, with which the voltage and current stress, power loss, thermal and electromagnetic performance can all be evaluated.
In the meanwhile, the Nuon Solar Team is also interested in designing a new motor drive with a higher efficiency and less weight. A promising solution is to apply the wide band gap (WBG) components including gallium nitride (GaN) and silicon carbide (SiC) in the motor drive. Thus, the characteristics of the WBG components especially the GaN MOSFET is investigated as well to clarify the feasibility of applying the WBG components to the application.
In overview, a systematic approach for the design of a GaN-based 4-parallel MOSFET motor drive is presented. The development of the motor drive is divided into 3 parts that are the 1-D modelling, hardware design and 3-D modelling. 1-D or 2-D model is sufficient to simulate the voltage and current stress, power loss, and highly simplified thermal and the electromagnetic performance. Only by using 3-D model the thermal and electromagnetic distribution can be thoroughly studied.
As the beginning, the load profile analysis is done to clarify the design requirements. Based on the requirements, several design candidates are proposed. Then, the 1-D modelling on the control system, power loss and thermal performance are done for each design candidates respectively. Built on the modelling and load profile, the efficiency and temperature of the motor drive in the competition WSC are predicted for each design candidates respectively. Among all the design candidates, the one with the highest efficiency and acceptable maximum junction temperature is selected. Based on the selection, the hardware design proceeds. Among all the hardware design, the layout design of the power stage is most important because it is used as the geometric shape in the 3-D modelling. Three different types of layout of the power stage are proposed.
To make the simulation closer to the reality, in the 3-D modelling, the thermal performance is coupled with the electromagnetic performance and the computational fluid dynamic (CFD). Through the 3-D electromagnetic modelling, the current distribution on the power stage with a certain layout is simulated. Based on the output result, the heat transfer is coupled with the CFD to analyze the heat transfer coefficient on the surface that has the forced convective cooling. Built on the output result, the stationary and time dependent heat transfer study are carried out to evaluate the temperature distribution when the car is cruising and the maximum junction temperature occurring when the large surge current comes. Finally, according to the simulated multi-physical performances, one of the three types of power stages is selected for the PCB construction.