Relationship of quality factor and hollow winding structure of Coreless Printed Spiral Winding (CPSW) inductor

Abstract

The principle of using hollow spiral winding is not novel, but the study on this topic is far from complete. In this paper, how hollow the central region of the Coreless Printed Spiral Winding (CPSW) inductor should be in order to achieve the maximal quality factor value Q max is explored. A new parameter, namely the ratio of the inner hollow radius and the outer winding radius τ = R in / R out , is proposed as an indicator for optimization and used to quantify how hollow a spiral winding is. With the aid of Finite Element Analysis (FEA), the relationship between τ and Q max , which depends on the operating frequency and the dimensional parameters of CPSW inductor, is established. For a specific operating frequency, it is discovered that if the conductor width is comparable with the skin depth, or the conductors are placed relatively far away from each others, the hollow design of the CPSW inductor has little improvement on Q but reduces the inductance. On the contrary, if the conductor width is much larger than the skin depth and the conductors are placed relatively close, the hollow spiral design is recommended. The optimal range of τ with which the Q max can be achieved is found to be around 0.45 to 0.55.

High-Speed (MHz) Series Resonant Converter (SRC) Using Multilayered Coreless Printed Circuit Board (PCB) Step-Down Power Transformer

“…Here, the inner radius of the transformer is considered as 4.5 mm that results in the outermost radius of approximately 10 mm. For increasing the effect of hollow factor, the width "w" of the winding should be considered as at least ten times of the skin depth corresponding to the operating frequency [9] of transformer. Here, it is approximately 8-10 times its skin depth corresponding to the operating frequency region of 2-4 MHz by also taking into the consideration of current carrying capability of the conductors.…”

“…Here, for the power transfer application of 50 W, the estimated primary inductance of the transformer is found to be approximately in the range of 6-8 μH in the operating frequency of 2-4 MHz with the transformer turn's ratio of 4:1. A hollow winding factor that is defined as the ratio of inner radius "R in " to that of the outermost radius "R out " [9] is considered as 0.45, in order to increase the quality factor "Q" and hence to reduce the dc resistance of the transformer. Here, the inner radius of the transformer is considered as 4.5 mm that results in the outermost radius of approximately 10 mm.…”

“…Even though there exists no magnetic core, the skin and proximity effects of the conductors play a dominant role at higher operating frequencies. Therefore, the recent study on the winding strategies, i.e., by introducing an optimum hollow factor [9] in the circular spiral inductor shows that the losses of the windings at higher operating frequencies can be reduced along with the improvement of the quality factor. Apart from this, different winding strategies were also investigated [1] to reduce the parasitic capacitances of multilayered coreless PCB inductor in order to operate in a wide operating frequency region.…”

Design and simulation of printed winding inductors for inductive wireless power charging applications

“…Recently planar spiral IA was intensively studied in order to define design guidelines concerning mainly the impact of the geometry on quality factor as function of working frequency [2]. The intrinsic limitations of the inductive WPT systems using spiral IA as function of the power transfer efficiency was addressed in [3].…”

“…The intrinsic limitations of the inductive WPT systems using spiral IA as function of the power transfer efficiency was addressed in [3]. Those studies were based on analytical calculation [3] or electromagnetic simulation [2]. No measurement benchmark was presented in order to validate the simulation approaches.…”