Analysis and Mitigation of Conducted Common-Mode Emissions in Solid-State Transformer

Solid-state transformers are potential solutions for power conversion applications with multiple ports, enabling the linking of renewable energy sources and asynchronous systems. However, the high dV/dt and parasitics in the transformer and switching devices can cause ringing (oscillation) in the collectors of the switching devices and transformers. This paper analyses the main causes of conducted common-mode emissions of solid-state transformers, including experimental measurement techniques for leakage inductance and parasitic capacitances of a transformer. In addition, the impacts of snubber and decoupling capacitors on the conducted emission and switching losses, considering single-phase shift and triple-phase shift modulations, are presented in time and frequency domains. On top of that, the effect of DC-link capacitor type on conducted emissions is investigated. Based on the experimental results, the parasitic capacitances of the switching devices and the transformer are the main propagation paths of the conducted common-mode emission. Decoupling capacitors reduce the high-frequency oscillations, but the value should be selected carefully to avoid resonance in the low-frequency ranges. Triple phase-shift modulation reduces the AC link reactive current, but it increases both conducted CM emissions and switching losses, while single phase-shift modulation increases the reactive power and reduces the conducted CM emissions.