Improving Power Quality in Aircraft Systems: Usage of Integrated LLCL Filter for Harmonic Mitigation

Switching harmonics, the main type of harmonics, are effectively suppressed using trap filters. This allows for smaller overall inductance and filter size, despite larger output filter components. However, trap inductors need more magnetic cores than traditional LCL filters. To reduce the size of output power filters, a magnetic integrated high-order LLCL filter with an LC-trap is proposed for avionics converters due to its excellent harmonic absorption and reduced size. This method extends the traditional integrated LCL filter by connecting the trap inductance in series with the filter capacitor. A design method to further reduce the size of output filter components will be developed. This is crucial as the integrated LLCL filter is the simplest form of integrated filters and will be used to address resonance issues. Rigorous network conditions are selected for analysis, and the filtering capabilities of integrated passive filters are extensively discussed. Strong grid conditions will be explored to verify the integrated LLCL filter. The simulation and hardware-in-the-loop (HIL) experimental results demonstrate that the proposed filter significantly reduces switching harmonics, achieving a total harmonic distortion (THD) of 0.80% in the injected current, which confirms the filter's high efficiency in harmonic absorption. Furthermore, the current ripples on the inverter side inductance remain minimal, ensuring optimal performance and durability.