On the relationship of quality factor and hollow winding structure of coreless printed spiral winding (CPSW) inductor

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 for a given footprint area in order to achieve the maximal quality factor Q max and to maintain high inductance value is explored. A hollow factor based on the ratio of the inner hollow radius and the outer winding radius τ = R in/R out, is proposed as for optimization and quantifying how hollow a spiral winding is. 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. If the conductor width is much larger than the skin depth and the conductors are closely placed, the hollow spiral design is recommended. The optimal range of τ with which the Q max can be achieved is found to be around 0.45-0.55. © 2006 IEEE.published_or_final_versio

PCB Layer Optimization of Planar Medium Frequency Transformer for On-Board EV Chargers

Planar medium frequency transformer (MFT) is a promising solution for on-board electric vehicle (EV) chargers, to achieve high power density and high efficiency. The trend towards higher power densities and higher efficiencies exposes a number of limitations on conventional litz wire transformers, especially for increasing the current density. Litz wire current density is limited by the temperature, due to poor thermal management capabilities. PCBs, however, have better thermal management capabilities, which allows for higher current densities. This paper optimizes planar MFT windings focusing on maximizing current density and the simplicity of the implementation. The losses, power density and thermal constraints are investigated and a pareto-front is created based on optimal solutions. High efficiency and power densities are achieved from 2D/3D FEM simulations. A solution within thermal constraints is selected and a prototype is built based on similar ratings. Tests with different current densities are carried out on the prototype and the temperatures are compared. The results verify that planar MFT with high current densities are feasible solutions for high efficiency and high power density MFTs

Electrical, thermal and electro-magnetic analyses of a 100 kHz interleaved power electronic transformer

In this paper, the finite element electrical, thermal and electro-magnetic analysis of an interleaved power electronic transformer structure operable at 100 kHz is presented. The analysed power electronic transformer structure is modelled with an EE-shaped core and interleaved primary and secondary windings. Electromagnetic analysis was done on the structure to study its properties like magnetic flux density, magnetic field, current density and relative permeability. Electrical and thermal analysis was done on the transformer to study its operating efficiencies and losses in isolation, buck and boost working modes. The analyses were done for different frequencies to ascertain that 100 kHz is the better choice of frequency for the designed power electronic transformer. The results are compared to a non-interleaved power electronic transformer structure to study the improvement obtained in the interleaved model. It was seen that transformer efficiencies of about 99 % could be obtained on using interleaved winding technique rather than non-interleaved method. Finite element modelling software-Altair FLUX was used to simulate the transformer and analytic equations were used to verify the obtained results

Contactless measurement of electric current using magnetic sensors

We review recent advances in magnetic sensors for DC/AC current transducers, especially novel AMR sensors and integrated fluxgates, and we make critical comparison of their properties. Most contactless electric current transducers use magnetic cores to concentrate the flux generated by the measured current and to shield the sensor against external magnetic fields. In order to achieve this, the magnetic core should be massive. We present coreless current transducers which are lightweight, linear and free of hysteresis and remanence. We also show how to suppress their weak point: crosstalk from external currents and magnetic fields

Losses and thermal considerations on an IPOS structure with 20kW high-frequency planar transformers

Nowadays power electronics is looking for more integrated and compact insulated DC/DC converters. Electrical machines, like transformers, have a fundamental role in those kinds of converters. One of the main integration issue is the thermal aspect due to the power losses. Moreover, in an insulated DC/DC converter the bulkiest device is the transformer. Based on the high frequency power application the adopted transformer could be planar or litz wounded technology. In this work a single phase planar transformer for high power application has been investigated. An IPOS structure connecting many planar transformers has been performed to cope with the limitations that a single component gives. An experimental set-up adopting a SiC H-bridge power module feeding the different transformer structure. A power losses comparison among different structures has been realized. Indeed, the comparison is made connecting the H-bridge to a: single phase planar transformer, IPOS with 2 transformers, IPOS with 5 transformers, IPOS with 6 trans- formers and IPOS with a 10 transformers. The paper proposes thermal simulations for the IPOS made by 10 transformers and experimental result