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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter has a high noise attenuation rate and is widely used. However, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter is not ideal for suppressing electromagnetic interference (EMI) noise. The symmetrical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter can improve the suppression effect of EMI noise while ensuring the harmonic suppression capability. However, the symmetrical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter adds two inductors compared to the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter, resulting in a significant increase in the volume and weight of the inverter system. This article analyzes the structure of the symmetrical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter, proposes coupling integration and decoupling integration solutions, adopts the planar magnetic integration method, and integrates the inductance of the symmetrical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter.