Abstract
D.Ing.
Changes in the preferred technologies used in modem switched mode power supplies are driven by the need for a decrease in cost of manufacturing while maintaining the highest possible power density. Modem materials allow smaller components to be manufactured without affecting their electromagnetic properties but thermal problems still impair efforts to further reduce their size. Increased switching frequencies cause increased conductor and core losses in magnetic components such as inductors and transformers.
Amongst other advantages the increased surface area of low-profile planar structures allow better removal of the heat generated in the component and this work reevaluates conductor optimization for specific planar inductor windings. Conductor optimization has been a topic thoroughly investigated over the last few decades and these techniques have been adopted for planar winding design. It will be shown that the process involved in the manufacturing of helical planar windings allows further exploitation of the basic optimization process. A per-layer optimization technique, earlier proposed by other researchers and deemed impractical at the time, is revised and it is shown here that it can be successfully implemented in the chosen winding type. The per-layer optimization is also extended to accommodate non-sinusoidal current waveforms in this work.
Other facets of loss reduction are also addressed. Windings are shaped in the region of air gaps in magnetic circuits to reduce the losses caused by the fringing flux intersecting the conductors but since the shaping influences both the ac-resistance and dc-resistance
of the winding an optimization process is required to find the optimal conductor arrangement. Contributions are made with regard to speeding up the process of finding the optimal layout of conductors around the air gap by devising a simple model for the flux distribution of the fringing flux.
The effect of combining the per-layer optimization technique with these shaping techniques is exploited to its full potential in this work and contributes largely to loss reduction in helical inductor windings carrying currents containing ac- and dc components. The optimization time is reduced by allowing winding shaping while maintaining the dc-resistance of each layer. The optimal winding shape then becomes a function of the window constraints for a chosen core rather than finding it through conventional methods.
Case studies, complete with FEM-simulations and experimental measurements, are offered in support of the proposed solutions.
Manufacturing issues are dealt with and loss measurement techniques developed as part of this work.