An Approach for the Design and Analysis of PCB Busbars in High Power SiC Inverters using FEA Tools.

ABERG, BRYCE. An Approach for the Design and Analysis of PCB Busbars in High Power SiC Inverters using FEA Tools. (Under the direction of Iqbal Husain). Wide band gap semiconductors, including silicon carbide (SiC) and gallium nitride (GaN), allow engineers to develop higher power density systems compared to traditional Si technology. Silicon Carbide, in particular, has promising applications to the automotive, aerospace, and utilities industries among others. Commonly used to create solid electrical and mechanical connections in high power systems, busbars are critical in ensuring system reliability in terms of voltage spike and temperature rise. Laminated busbars, commonly consisting of heavy copper planes separated by a non-conductive substrate, are widely used in industry due to their mechanical, electrical, and thermal robustness. Printed circuit boards (PCB) have advantages over laminated busbars in developing high power density systems. While the optimization of laminated busbar design has been widely reported, high power PCB busbars are less represented in literature. Therefore, a simulation-based methodology used to analyze and optimize the design of PCB busbars using finite element analysis (FEA) tools will be discussed. Two systems were considered for these studies including a 135 kW SiC traction inverter and a 125 kVA SiC inverter used in an active harmonic filter. Components comprising the power loop, including the PCB busbar, power module, and heavy duty interconects were modeled in Q3D to extract the loop inductance for both systems. The two experimental methods used to validate simulation results included double pulse tests (DPT) and impedance measurements. The busbar design in the 135 kW system was optimized using Ansys Q3D, resulting in a 19 % reduction in voltage spike amplitude according to double pulse tests. The loop inductance in the 135 kW system was also measured using an impedance analyzer and there was a less than 5 % difference between measured and simulated inductance values. These experimental results validated the simulation-based approach to analyzing PCB busbars and these same methods were applied to the PCB bussing system in the 125 kVA inverter during the project’s design phase. The study of the 125 kVA SiC inverter’s PCB busbar included an analysis of its design to determine its effect on the system in terms of voltage spikes and temperature rise. The methods from the previous section were extended to demonstrate how the extracted loop inductance from Q3D can be used to define the minimum required decoupling capacitance for a system. The FEA analysis approach was extended to include a thermal-electric simulation to verify the PCB busbar will have an acceptable worst-case temperature rise. Extracted loop inductance from impedance measurements agreed with simulation results, indicating FEA analysis of parasitic loop inductance can have acceptable accuracy. By analyzing two different systems, this simulation-based analysis approach was shown to be appropriate for analyzing specific reliability metrics for any high power system utilizing a PCB busbar. © Copyright 2018 by Bryce Aberg