Analysis of Conducted EMI for Dual Active Bridge DC-DC Converter in an Electric Traction Application

Dual active bridge (DAB) converters are commonly used in power conversion applications with switching devices that operate at high frequencies and high switching speeds. There can be current ringing (oscillation) both in the collector of the switching devices and in the transformer due to the high dv/dt and the parasitics in the transformer and the switching devices. This paper analyses the main causes of common-mode and differential-mode conducted electromagnetic interference (EMI) by focusing on the high dv/dt, high switching frequency, the dominant parasitics of the switching device, and the transformer. Based on the simulations, the parasitics and non-linearity behaviour of the switching devices, and transformer parasitics are the main causes of the conducted EMI. In addition, increasing the switching frequency increases both the power loss and conducted EMI because the parasitic capacitances become dominant at high frequencies. To quantify the influences of the parasitic capacitances and the nonlinear behaviour of the switching device, both time domain and frequency domain analysis for the sources of the conduced EMI and some mitigation techniques using Saber^® simulator is presented. On top of that, the effect of the transformer magnetising inductance on soft switching is studied.