John G. Hayes

Power-Factor-Corrected Single-Stage Inductive Charger for Electric Vehicle Batteries

A novel power-factor-corrected single-stage alternating current/direct current converter for inductive charging of electric vehicle batteries is introduced. The resonant converter uses the current-source characteristic of the series-parallel topology to provide power-factor correction over a wide output power range from zero to full load. Some design guidelines for this converter are outlined. An approximate small-signal model of the converter is also presented. Experimental results verify the operation of the new converter

Wide-load-range resonant converter supplying the SAE J-1773 electric vehicle inductive charging interface

The recommended practice for electric vehicle battery charging using inductive coupling (SAE J-1773), published in January 1995 by the Society of Automotive Engineers, Inc., outlines values and tolerances for critical vehicle inlet parameters which must be considered when selecting a coupler driving topology. The inductive coupling vehicle inlet contains a significant discrete capacitive component in addition to low magnetizing and high leakage inductances. Driving the vehicle interface with a variable-frequency series-resonant power converter results in a four-element topology with many desirable features: unity transformer turns ratio; buck/boost voltage gain; current-source operation; monotonic power transfer characteristic over a wide load range; throttling capability down to no load; high-frequency operation; narrow modulation frequency range; use of zero-voltage-switched MOSFETs with slow integral diodes; high efficiency; inherent short-circuit protection; soft recovery of output rectifiers; and secondary d/spl nu//dt control and current waveshaping for the cable, coupler and vehicle inlet, resulting in enhanced electromagnetic compatibility. In this paper, characteristics of the topology are derived and analyzed using two methods. Firstly, the fundamental mode AC sine-wave approximation is extended to battery loads and provides a simple, yet insightful, analysis of the topology. A second method of analysis is based on the more accurate, but complex, time-based modal approach. Finally, typical experimental results verify the analysis of the topology presented in the paper.

Simplified electric vehicle power train models and range estimation

In this paper, simplified EV power train models are developed for new and existing production vehicles. The models are developed based on published vehicle parameters and range information for the Nissan Leaf and the Tesla Roadster. The models are compared with published manufacturer specifications for range under various route and driving conditions, and for various drive cycles. The models are additionally validated against test results for the Nissan Leaf and Tesla Roadster vehicles, where the test route topography is modeled using Google Earth and a GPS-based smart-phone application. Excellent correlations are demonstrated between the experimental results and manufacturer data and the vehicle models. Impacts of battery degradation with time and vehicle HVAC loads are considered in the study.

CCTT-Core Split-Winding Integrated Magnetic for High-Power DC–DC Converters

A novel CCTT-core split-winding integrated magnetic (IM) structure is presented in this paper. The IM device is optimized for use in high-power dc–dc converters. The IM structure uses a split-winding configuration which allows for the reduction of external leakage inductance, which is a problem for many IM designs. Magnetic poles are incorporated to help shape and contain the leakage flux within the core window. Low-cost and low-power loss ferrite is used which results in a very efficient design. An IM reluctance model is developed which uses fringing equations to develop a more accurate design. An IM design algorithm is developed and implemented in Mathematica for design and optimization. FEA and experimental results from a 72 kW, (155-V dc, 465-A dc input, and 420-V dc output) prototype validate the new IM concept. The 72 kW CCTT- core IM was shown to be 99.7% efficient at full load.

Magnetic Material Selection for High Power High Frequency Inductors in DC-DC Converters

Dc-dc converter size and efficiency are driving factors in industrial, aerospace and automotive applications. Thus, optimal component selection is essential for a compact design. The inductor often appears as the converters largest component. This paper presents analytical and experimental comparisons of the magnetic materials used in a practical design. The investigation is concerned with magnetic material selection for a dc-dc power inductor in the medium (20 kHz) to high (150 kHz) frequency range and the low (1%) to high (220%) current ripple range. The materials under investigation are iron-based amorphous metal, silicon steel, nanocrystalline, ferrite, powdered iron and gap-less powder materials. A newly developed silicon steel material from JFE-Steel Co. is presented. A novel material comparison which includes thermal conductivity and saturation capability is proposed. The area product analysis for material comparison is presented for 10 kW dc-dc inductor design examples. The variation of core power loss with dc-bias is experimentally investigated for different materials. A 1.25 kW half-bridge dc-dc converter is used in experimental validation.

Inductance characterization of high-leakage transformers

In this paper the inductances of high-leakage transformers are investigated by analysis, measurement, and finite-element simulation. Series-coupling tests, featuring differential coupling (series opposing) and cumulative coupling (series aiding), are conducted in addition to the standard open-circuit and short-circuit tests. This paper initially reviews and discusses the various test approach featuring the open-circuit, short-circuit and series-coupling tests. Two very different types of high-leakage transformers are then characterized based on these tests. The short-circuit and series-coupling tests performed comparably for investigating the spatial variations of the primary and secondary leakage inductances of the high-power, high-leakage transformer first investigated. For the second low-power, high-leakage, high-resistance planar transformer the differential-coupling test proves to be a more useful, accurate, and insightful test than the short-circuit test.

Revised Magnetics Performance Factors and Experimental Comparison of High-Flux Materials for High-Current DC–DC Inductors

High-flux-density materials, such as iron-based amorphous metal and 6.5% silicon steel for gapped inductors, and powdered alloys for gapless inductors, are very competitive for high-power-density inductors. The high-flux-density materials lead to low weight/volume solutions for high-power dc-dc converters used in hybrid-electric and electric vehicles. In this paper, the analytical selection of the magnetic materials is investigated, and modified performance factors are introduced for convection- and conduction-cooled magnetic components. The practical effects of frequency, dc bias, flux-density derating, duty cycle, airgap fringing on the core loss, and thermal configuration based on lamination direction are investigated for iron-based amorphous metal, 6.5% silicon steel, and iron-based powdered alloy material. A 2.5-kW converter is built to verify the optimum material selection and thermal configuration. Analytical, simulation, and experimental results are presented.

An ultra-compact transformer for a 100 W to 120 kW inductive coupler for electric vehicle battery charging

A new generation of electric vehicles is being developed. A key problem to be solved is that of charging the batteries. One means of charging uses inductive coupling. The inductive coupling approach is essentially a transformer with a removable primary winding connected to a charging unit via a cable. The secondary and the core of the transformer are on the vehicle. This paper presents an inductive coupler which has been demonstrated delivering from 100 W to 120 kW continuously at a frequency of 75 to 120 kHz. The transformer is very compact (<100 in/sup 3/). The primary purpose of this paper is a discussion of the power transformer. In addition the paper briefly addresses how the design of a magnetic device, which is usually a strictly technical exercise between engineers, is impacted when it is directly accessible to consumers in a mass market.

Magnetic Material Comparisons for High-Current Inductors in Low-Medium Frequency DC-DC Converters

The low component count, high full-load efficiency and simplicity of hard-switched dc-dc converters in the low to medium frequency range lead to a low cost and low weight/volume solution for high-power dc-dc converters. The choice of the magnetic material is critical in order to optimise the size of the inductor. In this paper, Fe-based amorphous metal, 6.5 % silicon steel, nanocrystaline, and low-frequency ferrite materials are analysed and investigated for use in a gapped CC-core inductor. A novel area product derivation method, which includes foil ac copper loss effects and core loss due to the gap, enables material comparisons over a range of frequencies and ripple ratios. As expected, inductor size for a given inductance decreases with increased frequency. Inductor size, however, can increase in the laminated materials due to increased air gap core loss effects. A 2.5 kW boost converter is built to verify the optimum material selection over the frequency range and ripple ratio of interest.

Novel CCTT-core split-winding integrated magnetic for High-Power DC-DC converters

A novel CCTT-core split-winding integrated magnetic (IM) structure is presented in this paper. The IM device is optimized for use in high-power dc-dc converters. The IM structure uses a split-winding configuration which allows for the reduction of external leakage inductance, which is a problem for many IM designs. Magnetic poles are incorporated to help shape and contain the leakage flux within the core window. Low cost and low power loss ferrite is used which results in a very efficient design. An IM design algorithm is developed and implemented in Mathematica for design and optimization. FEA and experimental results from a 80 kW prototype validates the new IM concept and the CCTT magnetic was shown to be 99.7% efficient at full load.