Cancellation of Leakage Currents through Power Module Baseplate Capacitance

The fast edge rates achievable by wide-bandgap semiconductors can produce significant common-mode leakage currents through the baseplates of encompassing power modules. Such common-mode currents can lead to elevated electromagnetic signatures. This paper provides a theoretical treatment of this common-mode behavior for a typical SiC half-bridge multi-chip power module in the context of a half-bridge inverter. A common-mode equivalent model is produced that identifies the distribution of the parasitic baseplate capacitance across the module terminals as the principal factor that controls the leakage current through the module baseplate. Furthermore, the model predicts that this leakage current can be manipulated and even canceled out by achieving a prescribed distribution of said baseplate capacitance for the system under investigation. These predictions are validated by a set of empirical studies in which compensating capacitors are affixed to the external terminals of a commercial multi-chip power module comprising a half-bridge inverter. The model predictions are shown to be in good agreement with the measured behavior of this system.