CM Noise Modeling and Reduction for Multi-Output Dual-Switch Flyback Auxiliary Power Supplies

The multi-output dual-switch flyback converter is extensively used as an auxiliary power supply in high-voltage and high-power photovoltaic (PV) inverters, providing power to electronic circuits. To maintain an independent power supply, isolation between the multiple outputs is necessary. However, when developing a common-mode (CM) model for the multi-output flyback converter as an independent system, neglecting the isolation between the multiple outputs renders the model incapable of accurately describing the CM electromagnetic interference (EMI) emission characteristics within the inverter system. To resolve this issue, this paper proposes a CM model for the multi-output flyback converter that effectively represents its CM EMI emission characteristics when used as an auxiliary power supply in an inverter system. First, a complete CM noise path model for the multi-output dual-switch flyback auxiliary power supply is established using the lumped capacitance model for isolating multiple outputs in transformers. Given the numerous lumped capacitors in the transformer's CM model, the “insertion capacitance method” has been proposed to accurately and reliably extract these capacitances. Subsequently, a capacitance designed for CM noise mitigation is implemented and adjusted to create a reverse extraction current, which offsets the generated CM noise. The established CM model accurately characterizes the transmission of CM EMI from the flyback auxiliary power supply through multiple output paths to other parts of the PV inverter. The effectiveness of this approach is validated on an experimental platform of a PV inverter.