A High Accuracy Characterization Method of Busbar Parasitic Capacitance for Three-level Converters Based on Vector Network Analyzer

Parasitic capacitance in power loop can impact switching performance of converters. Depending on the locations of those capacitors, they can mitigate switching stress if paralleled to DC-link capacitors, or introduce additional switching loss if paralleled to device output capacitance, Coss, or intensify common-mode EMI noise if paralleled to switching-node stray capacitance. Thus high-accuracy characterization of parasitic capacitance is necessary to estimate the performance of converter. This paper proposes novel method to measure stray capacitance in laminated busbar. Such method is based on a vector network analyzer (VNA). The direct assessment of each node-to-node capacitance is the key advantage compared to the traditional method. It also simplifies measurement process, avoids complicated math operation, and improves measurement accuracy in applications of assessing capacitance of the multiple-node systems, for example, three-level converters. This paper illustrates proposed method by measuring a laminated busbar. Design of customized fixtures is discussed for improving measurement consistency and accuracy. Measurement results are compared to the traditional method and ANSYS Q3D simulation to prove its accuracy.