Design of Planar Magnetic Integrated Symmetrical Harmonic Filter With Reduced EMI Noise in the Grid-Connected Inverter

The inverter is an essential power conversion device in the power generation system, but the output current by the inverter system contains a large number of harmonics, and harmonic filters need to be used for harmonic suppression to meet grid connection standards. As a third-order filter, the LCL filter has a high noise attenuation rate and is widely used. However, the LCL filter is not ideal for suppressing electromagnetic interference (EMI) noise. The symmetrical LCL filter can improve the suppression effect of EMI noise while ensuring the harmonic suppression capability. However, the symmetrical LCL filter adds two inductors compared to the LCL filter, resulting in a significant increase in the volume and weight of the inverter system. This article analyzes the structure of the symmetrical LCL filter, proposes coupling integration and decoupling integration solutions, adopts the planar magnetic integration method, and integrates the inductance of the symmetrical LCL filter into the same EI magnetic core by rationally designing the winding structure, greatly reducing the size and weight of the filter. Finally, the simulation and GaN-based experimental platform are built to verify the harmonic suppression effect and EMI suppression effect of the designed magnetically integrated symmetrical LCL filter.