Tomio Yasuda

Compact contactless power transfer system for electric vehicles

Electric vehicles (EVs) have been attracting considerable interest recently. A contactless power transfer system is required for EVs. Transformers can have single-sided or double-sided windings. Transformers with double-sided windings are expected to be more compact and lightweight than transformers with single-sided windings. A contactless power transfer system for EVs needs to have a high efficiency, a large air gap, good tolerance to misalignment and be compact and lightweight. In this paper, a novel transformer using series and parallel capacitors with rectangular cores and double-sided windings that satisfies these criteria has been developed, and its characteristics are described. It has an output power of 1.5 kW and an efficiency of 95% in the normal position. To reduce the cost of expensive ferrite cores, a transformer with split cores is also proposed.

A large air gap 3 kW wireless power transfer system for electric vehicles

A wireless power transfer system for electric vehicles is required to have high efficiency, a large air gap, and good tolerance for misalignment in the lateral direction and to be compact and lightweight. A new 3 kW transformer has been developed to satisfy these criteria using a novel H-shaped core and split primary capacitors. The design procedure based on the coupling factor k, the windings Q, and the core loss is described. An efficiency of 90% was achieved across a 200 mm air gap.

Small-size light-weight transformer with new core structure for contactless electric vehicle power transfer system

A contactless power transfer system for electric vehicles is required to have high efficiency, a large air gap, good tolerance to misalignment in the lateral direction, and be compact and lightweight. A new 1.5 kW transformer has been developed to satisfy these criteria using novel H-shaped cores, which is more efficient, more robust to misalignment, and lighter than previously employed rectangular cores, and its characteristics are described. An efficiency of 95% was achieved across a 70 mm air gap. The results of test at wide air gap of 100mm, temperature rise test and 3kW operation test are also presented.

A 10kW transformer with a novel cooling structure of a contactless power transfer system for electric vehicles

A contactless power transfer system for electric vehicles is required to have high efficiency, a large air gap, good tolerance to misalignment in the lateral direction, and to be compact and lightweight. A new 10kW transformer with double-sided winding for fast charging has been developed. The proposed transformer has a novel cooling structure using aluminum bars, aluminum junctions, and aluminum plates. In this paper, the design concept, specifications, and test results of the new transformer are described. The other feature of this transformer is its interoperability with a 3kW transformer. The interoperability test results are also shown.

Bidirectional contactless power transfer system expandable from unidirectional system

Contactless power transfer (CPT) systems with primary series and secondary parallel capacitors (SP topology) are useful for charging electric vehicles. However, SP topology is not suitable for bidirectional power transfer. This paper introduces a novel SPL topology for bidirectional CPT systems that is realized by adding an inductor and an inverter to the SP topology. The 3 kW and 160 mm gap bidirectional test results show that the efficiency of G2V is 92.5%, and the efficiency of V2G is 93.4%, which are approximately equal to the efficiency of the unidirectional SP topology system of 93.1%.

Contactless charging systems

Two technologies have greatly accelerated the practical use of contactless charging systems: the contactless power transformer achieved a compact size and good tolerance to misalignment by improving the core architecture, while the charging controller raised effectiveness and lowered noise with a new DC/DC converter. Specifically, the new DC/DC converter can operate buck-boost and soft-switching. A bench test and PHEV test confirmed that a contactless charging system composed of these new technologies charged stably despite gap changes and misalignment.

A moving wireless power transfer system applicable to a stationary system

Solving a short mileage and a long charging time is indispensable to putting electrical vehicles (EVs) on the full-scale market. A moving wireless power transfer (WPT) system is one of the effective solutions, because it can feed electric power to moving EVs. This paper proposes a moving WPT system consisting of several stationary ground-side (primary) coils and a moving vehicle-side (secondary) coil. This system is characterized by the use of the common vehicle-side coil to both moving and stationary WPT situations. Theoretical analysis concludes that the moving WPT system resulting from a stationary WPT system is the same in equivalent circuit as the stationary system. The moving WPT system employs solenoid coils that are superior to circular coils in terms of misalignment and flux-distribution performance. A downscaled moving WPT system rated at 3 kW is designed, constructed, and tested to verify the principles of operation, and the capability of continuous power transfer.

A Dynamic Wireless Power Transfer System Applicable to a Stationary System

Solving a short mileage and a long charging time is indispensable in putting electrical vehicles (EVs) on the full-scale market. A dynamic wireless power transfer (WPT) system is one of the effective solutions, because it can feed electric power to moving EVs. This paper proposes a dynamic WPT system consisting of several stationary ground-side (primary) coils and a moving vehicle-side (secondary) coil. This system is characterized by the use of the common vehicle-side coil to both dynamic and stationary WPT situations. Theoretical analysis concludes that the dynamic WPT system resulting from a stationary WPT system is the same in equivalent circuit as the stationary system. The dynamic WPT system employs solenoid coils that are superior to circular coils in terms of misalignment and flux-distribution performance. A downscaled dynamic WPT system rated at 3 kW is designed, constructed, and tested to verify the principles of operation, and the capability of continuous power transfer.

A wireless power transfer system with a double-current rectifier for EVs

The secondary coil installed on an EV is required to be small in size, light in weight, and efficient in power transfer, as well as tolerant in lateral misalignment with a large air gap. Also, a wireless power transfer (WPT) system needs high power transfer. Both downsizing and high power transfer bring a thermal problem the secondary coil. This paper proposes a WPT system combining the so-called “series and series” connected resonant capacitors with a double-current rectifier to achieve a secondary coil current reduction that is an essential matter of the problem. The proposed WPT system employs solenoid coils that are superior to circular coils in terms of misalignment and flux-distribution performance. The secondary WPT coil rated at 18 A is designed, constructed, and tested to verify the principles of operation. The system efficiency is 90.0% at nominal air gap 135 mm without misalignment in output power 7 kW.

Investigation of wireless power transfer system with spaced arranged primary H-shaped core coils for moving EVs

As a solution for long charging time and short running range of EVs, research on wireless power transfer systems for moving EVs have been getting attention. Although several power transfer systems with single or multiple grounded coils have been proposed, those systems have difficulties in maintenance, and require high system implementation and maintenance cost. In this paper, we evaluate the performance of a proposed wireless power transfer system for moving EVs, composed by a row of evenly spaced H-shaped core coils. With two types of resonance circuit, SP and SS topology, the performance of the system is evaluated under a constant voltage operation and a constant current operation. Comparison of the performance of the system with each resonance circuit in each operation is presented from the aspect of power output, efficiency and power factor. Among all experiment cases, power transfer with average transformer efficiency above 85% is achieved.