Differential Mode and Common Mode Modeling of Pulse Transformers for Gate-Driver Applications

Overview & Synopsis

The higher switching speed attainments of WBG power devices such as silicon carbide (SiC) MOSFETs, and their ability to operate at higher switching frequencies, becomes conflicting when challenged with electromagnetic interference (EMI) issues. The objective of this dissertation is to improve the design of pulse transformers integrated in an intermediate stage of a power converter system, known as a gate-driver. The main goal is to mitigate the parasitic capacitances of these transformers, which are the source originators of common mode (CM) currents. A modelling and simulation scheme of pulse transformers with alternative shielding structures has been developed. The transformer is primarily designed using Altium Designer while respecting IPC-2221 standards. Its geometry is then exported into ANSYS Q3D Extractor, where an equivalent circuit model is extracted. The correlation of the susceptibility of pulse transformers comprising different shielding structures is simulated by applying pulses of 1.4 kV amplitude, representing a dv/dt of 125 kV/μs, between the primary and secondary distinctive grounds. The influence of the shielding configuration, and the variation of its length, width and thickness is explored. In addition to the applied simulation analysis, an equivalent experimental examination was conducted after manufacturing the studied transformers. The correspondence of the simulation and experimental results permitted the validation of the models.