Abstract
At high frequency, AC resistance of a printed circuit board (PCB) winding becomes important and accounts for a large proportion of planar transformer losses. The winding is then influenced by both skin and proximity phenomenon, which makes the current distribution uneven resulting in an increased resistance. The study of improving AC resistance of a PCB winding has been tackled by many researchers. However, the lack of an overview and comparison among improvements has made it difficult to apply those methods to a specific winding. To overcome the above limitations, this paper investigates the pros and cons of three popular AC resistance optimizing methods: optimizing track width of a solid PCB winding, using multi-strands and using Litz style PCB winding. To verify the theoretical analysis, a total of 12 PCBs are simulated by finite element (FEM) and tested in the laboratory. Five criteria are analyzed, including skin resistance, proximity resistance, AC to DC ratio, total AC resistance and complexity are taken into consideration. The results of this study show that optimizing track width method has a significant improvement on AC resistance while the use of Litz PCB is effective for applications that need stable AC resistance in a wide frequency range. The use of parallel strands winding should be carefully considered as there is not significant benefit in both reducing the AC resistance and AC to DC ratio.
Highlights
In recent years, the outbreak of the renewable energy industry and electric vehicles have increased the demand for power conversion systems: micro-grid inverter, wireless chargers, bi-directional converters
The results of this study show that optimizing track width method has a significant improvement on AC resistance while the use of Litz printed circuit board (PCB) is effective for applications that need stable AC resistance in a wide frequency range
To better understand the behaviour of different PCB windings, measurements are done in a range from 1 MHz to 15 MHz, which is known as frequency range of higher order harmonics of power converters
Summary
The outbreak of the renewable energy industry and electric vehicles have increased the demand for power conversion systems: micro-grid inverter, wireless chargers, bi-directional converters. Electromagnetic devices, which are known to take a lot of space in power converters, become more compact thanks to the increasing of switching frequency to hundreds of kHz [1] and have created potential opportunities for using planar structures with spiral windings to replace conventional transformers. Many researches on improving AC resistance of transformer windings have been done previously with key ideas of interleaving windings, arranging positions or adjusting dimensions of each turn to reduce skin and proximity losses. They can be divided into three main research topics as follows
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