Abstract
This paper describes a novel contactless power transfer (CPT) system with geometrically improved H-shape ferromagnetic cores and electromagnetically prospective modelling analysis methods for wireless power transmitting (WPT) applications of electric vehicles (EVs). A CPT prototype, using optimized H-shaped magnetic couplers and series-to-series (SS) compensation, is proposed to address and ensure the maximization of system efficiency, power transfer ratings, and air gaps of coupling coils. By focusing on the main factors such as various system operating frequencies, different geometric designs of coils, changeable inductive coupling distances, electromagnetic field performances and actual phase angle deviations when the inductive coupling system tends to be stable with its waveforms, this small-sized H-shape CPT system has been analytically considered and modelled in a finite-element method (FEM) environment, resulting in a maximum system efficiency of 59.5%, a coil transmitting efficiency of 83.8% and a maximum power output of 42.81 kW on the load end when the resonant coupling of CPT system tends to occur within a range of calculated resonant frequencies, with an air gap of 10 mm. Moreover, the system efficiency and coil transmitting efficiency can reach 47.75% and 77.22%, respectively, and the highest RMS real power to load can achieve 31.95 kW with an air gap of 20 mm. Besides, with an air gap of 30mm, this H-shape CPT system is measured to output 20.39-kW RMS power, along with the maximum system efficiency and coil efficiency of 41.78% and 63.23%, respectively. Furthermore, the improvements of flux linkage, magnetic flux density regarding the actual electromagnetic performance produced and the issues on the calculated natural resonant frequencies have been studied by result analysis and comparison of electromagnetic field parameters generated. In addition, the current limitations and further design considerations have been discussed in this paper.
Highlights
Over the past decades, there has been a growing tendency for developing environment friendly energy usage all over the world due to the increasing concerns on the reduction of conventional fossil fuels, environment pollution and the global climate change issues, for which the development progress on electric vehicles (EVs) and hybrid electric vehicles (HEVs) has been driven rapidly forward
Flux linkage and currents based on electromagnetic field performanceOptimal flux linkage and currents with a 10-mm air gap based on electromagnetic metrics: To investigate the actual electromagnetic field system performance of the contactless power transfer (CPT) coupler proposed, the flux linkage λ and coil current i are required to be addressed
H-shape cores, both the vector arrows of magnetic flux density B and magnetic field strength H tend to be able to reach their peak magnitude values at the edged corner of the very end points of the H-shape cores, with maximum scalar values of 9.364 x10^(-1) Tesla and 1.2608 x10^5 ampere per meter (A/m), respectively From Figure 5, it can be found that both the alternating flux linkage waveforms of two coils tend to be stable sinusoidal AC waveforms since about 0.5 ms onwards, which means the CPT system electromagnetic stability is able to be immediately established after only 4 periods
Summary
There has been a growing tendency for developing environment friendly energy usage all over the world due to the increasing concerns on the reduction of conventional fossil fuels, environment pollution and the global climate change issues, for which the development progress on electric vehicles (EVs) and hybrid electric vehicles (HEVs) has been driven rapidly forward. EVs have shown its advantages on addressing most of the environmental challenges while reliability and safety concerns of the traditional plug-in EVs are still obstructions. The contactless power transfer (CPT) technology has capabilities to allow eliminations of cables, slip rings and exposed plugs, which could increase the charging safety with no sparkling and the reliability under extreme environmental conditions. Based on the wireless power transmitting (WPT) proposed by Nikola Tesla, the fundamental principles of Faraday’s law of induction and Maxwell’s equations [1,2] in the 19th century, the contactless power transfer (CPT) using loosely coupled inductive energy transfer or electromagnetic resonant coupling could show the main advantages such as wireless charging convenience and charging implementation safety especially in dusty or humid conditions. A 2-kW circular pads based inductive power transmitting (IPT) model with 700mm diameter windings and 200-mm charging air gap was constructed and tested in 3D FEM software in [3] , which examined that this circular pad modular can result in satisfactory outputs
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