When flat wire inductors employ distributed windings, the proximity effect significantly exacerbates losses. The proximity effect refers to the uneven current distribution among multiple conductors when multiple conductors are arranged side-by-side and energized with alternating current, caused by the interaction of their magnetic fields, especially when the conductors are close together. This effect leads to current concentration on adjacent sides of the conductors, increasing local current density, effective resistance, and consequently, additional copper losses and temperature rise, affecting the inductor's efficiency and reliability.
In the distributed windings of flat wire inductors, conductors are typically closely packed to achieve a high slot fill factor, further aggravating the proximity effect. When high-frequency current passes through, the magnetic field interaction between conductors induces eddy currents, which superimpose with the original current, resulting in an even more uneven current distribution. This magnetic field distortion is particularly severe near the core or air gap, making the proximity effect losses even more significant. These losses not only reduce inductor efficiency but can also cause localized overheating, damaging the insulation material and shortening the inductor's lifespan.
To mitigate losses caused by the proximity effect, improvements can be made in winding design, conductor structure, and core optimization. In winding design, layered or staggered winding can effectively reduce the impact of proximity effects. Layered winding divides the conductor into multiple layers, with each layer isolated by insulation material, resulting in a more uniform magnetic field distribution between layers and reducing eddy current generation. Staggered winding adjusts the arrangement of conductors, causing the current in adjacent conductors to flow in opposite directions, thus partially canceling out the magnetic field and reducing losses caused by proximity effects.
Optimizing the conductor structure is also crucial for suppressing proximity effects. Flat wire inductors typically use flat copper wire with a rectangular cross-section, which offers a higher slot fill factor and better heat dissipation compared to round wire. However, flat wire conductors are more susceptible to proximity effects at high frequencies. Therefore, current distribution can be improved by adjusting the conductor's aspect ratio, increasing the insulation thickness between conductors, or using conductors with special geometries. For example, designing conductors with grooves or protrusions can increase the equivalent distance between conductors, reducing magnetic field coupling and thus lowering losses caused by proximity effects.
Optimized core design is also essential for suppressing proximity effects. The core material, shape, and air gap position all affect the magnetic field distribution. Using low-loss core materials, such as high-silicon steel sheets or ferrite, can reduce hysteresis and eddy current losses. Simultaneously, optimizing the core shape and air gap location can improve the uniformity of the magnetic field distribution within the winding window, reducing proximity effect losses caused by magnetic field distortion. For example, moving the air gap to the core edge or employing a distributed magnetic pressure structure can effectively reduce the magnetic field strength within the coil window, thereby reducing eddy current generation.
Furthermore, employing novel manufacturing processes and technologies is also an effective way to suppress proximity effects. For instance, 3D printing technology can create conductors and core structures with complex geometries, fundamentally reducing losses caused by proximity effects by precisely controlling the current density distribution and magnetic field path of the conductor. This technology not only increases design freedom but also provides new possibilities for inductor optimization.
