John T. Boys

Inductive Power Transfer

Inductive power transfer (IPT) was an engineering curiosity less than 30 years ago, but, at that time, it has grown to be an important technology in a variety of applications. The paper looks at the background to IPT and how its development was based on sound engineering principles leading on to factory automation and growing to a

Design and Optimization of Circular Magnetic Structures for Lumped Inductive Power Transfer Systems

1 billion industry in the process. Since then applications for the technology have diversified and at the same time become more technically challenging, especially for the static and dynamic charging of electric vehicles (EVs), where IPT offers possibilities that no other technology can match. Here, systems that are ten times more powerful, more tolerant of misalignment, safer, and more efficient may be achievable, and if they are, IPT can transform our society. The challenges are significant but the technology is promising.

Modern Trends in Inductive Power Transfer for Transportation Applications

A solution that enables safe, efficient, and convenient overnight recharging of electric vehicles is needed. Inductive power transfer (IPT) is capable of meeting these needs, however, the main limiting factor is the performance of the magnetic structures (termed power pads) that help transfer power efficiently. These should transfer 2-5 kW with a large air gap and have good tolerance to misalignment. Durability, low weight, and cost efficiency are also critical. 3-D finite-element analysis modeling is used to optimize circular power pads. This technique is viable, since measured and simulated results differ by 10% at most. A sample of power pads was considered in this work, and key design parameters were investigated to determine their influence on coupled power and operation. A final 2 kW 700-mm-diameter pad was constructed and tested having a horizontal radial tolerance of 130 mm (equivalent to a circular charging zone of diameter 260 mm) with a 200 mm air gap. The leakage magnetic flux of a charging system was investigated via simulation and measurement. The proposed pads meet human exposure regulations with measurement techniques specific by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) which uses the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines as a foundation.

Development of a Single-Sided Flux Magnetic Coupler for Electric Vehicle IPT Charging Systems

Inductive power transfer (IPT) has progressed to be a power distribution system offering significant benefits in modern automation systems and particularly so in stringent environments. Here, the same technology may be used in very dirty environments and in a clean room manufacture. This paper reviews the development of simple factory automation (FA) IPT systems for both todays complex applications and onward to a much more challenging application-IPT roadway. The underpinning of all IPT technology is two strongly coupled coils operating at resonance to transfer power efficiently. Over time the air-gap, efficiency, coupling factor, and power transfer capability have significantly improved. New magnetic concepts are introduced to allow misalignment, enabling IPT systems to migrate from overhead monorails to the floor. However, the demands of IPT roadway bring about significant challenges. Here, compared with the best FA practice, air-gaps need to be 100 times larger, power levels greater than ten times, system losses ten times lower to meet efficiency requirements, and systems from different manufacturers must be interoperable over the full range of operation. This paper describes how roadway challenges are being met and outlines the problems that still exist and the solutions designers are finding to them.

A Three-Phase Inductive Power Transfer System for Roadway-Powered Vehicles

Inductive power transfer is a practical method for recharging electric vehicles because it is safe, convenient, and reliable. The performance of the magnetic couplers that transfer power determines the overall feasibility of a complete system. Circular couplers are the most common topology in the literature; however, they have fundamentally limited coupling. Their flux patterns necessarily limit the operational air gap as well as tolerance to horizontal misalignment. A new polarized coupler topology [referred to as a double D (DD)] is presented, which overcomes these difficulties. DDs provide a charge zone five times larger than that possible with circular pads for a similar material cost and are smaller. A 0.31-m2 DD enables 2 kW of power transfer over an oval area measuring 540 mm × 800 mm with a 200-mm air gap. Leakage magnetic fields have been investigated and show that circular and DD couplers operating under similar power transfer conditions produce similar levels. Both topologies can be designed and operated to ensure compliance with international guidelines.

A Unity-Power-Factor IPT Pickup for High-Power Applications

The development of a new three-phase bipolar inductive power transfer system that provides power across the entire width of a roadway surface for automatic guided vehicles and people mover systems is described. A prototype system was constructed to verify the feasibility of the design for a number of moving loads (toy cars). Here, 40 A/phase is supplied at 38.4 kHz to a 13-m-long test track. Flat pickups are used on the underside of each vehicle to couple power from the track to the vehicle. Finite element modeling software was used to design the geometrical position of the track cables and to predict the power output. This design resulted in a considerably wider power delivery zone than possible using a single-phase track layout and has been experimentally verified. Mutual coupling effects between the various track phases require additional compensation to be added to ensure balanced three-phase currents.

Development and evaluation of single sided flux couplers for contactless electric vehicle charging

This paper describes the design of a new unity-power-factor inductive-power-transfer (IPT) pickup using an LCL tuned network for application in high-power systems. This new topology has the potential to increase the efficiency and reduce the cost of high-power pickups by minimizing the reactive currents in the pickup coil and the reflected VAR loading on the power supply. In a practical system, the rectifier and associated processing circuitry distorts the current waveforms, adding an effective inductive loading to the pickup circuit. A series compensation capacitor is added to correct this loading. A design strategy is developed for the new topology, and two example circuits are constructed and compared experimentally with a traditional parallel-tuned (LC) pickup operating on a monorail-based IPT system.

Multiphase Pickups for Large Lateral Tolerance Contactless Power-Transfer Systems

Inductive Power Transfer (IPT) is a practical and preferable method for recharging stationary and moving Electric Vehicles (EV) because it is safe, convenient and reliable. The performance of the magnetic couplers that transfer power determines the overall feasibility of a complete system. Single sided flux couplers have a unidirectional flux pattern and can be used under an EV with minimal loss to the (steel) chassis. Circular pads are single sided and the most common topology and these are investigated with consideration of magnetic field leakage guidelines. Following this, a new polarized coupler topology (referred to as a “Double-D-Quadrature” (DDQ)) is presented. An interoperability study with conventional circular couplers shows this DDQ pad is completely compatible and offers a significantly larger charge zone.

A new IPT magnetic coupler for electric vehicle charging systems

The majority of commercial contactless power-transfer systems used in manufacturing applications can only tolerate limited movement of the power pickup relative to the track to which it is magnetically coupled. This paper describes a new multiphase (quadrature) pickup that significantly improves the tolerance of the power receiver to such relative movement, enabling expanded applications such as continuously powered automatic guided vehicles, robots, and other vehicles to be considered. The advantage gained is largely independent of the track type, so that single-phase or multiphase tracks can be used as desired to improve both the power transfer and lateral tolerance as required. The improvement is achieved by capturing both vertical and horizontal components of magnetic flux around any track.

The design of a contact-less energy transfer system for a people mover system

Inductive Power Transfer (IPT) is a practical method for recharging Electric Vehicles (EVs) because is it safe, efficient and convenient. Couplers or Power Pads are the power transmitters and receivers used with such contactless charging systems. Due to improvements in power electronic components, the performance and efficiency of an IPT system is largely determined by the coupling or flux linkage between these pads. Conventional couplers are based on circular pad designs and due to their geometry have fundamentally limited magnetic flux above the pad. This results in poor coupling at any realistic spacing between the ground pad and the vehicle pickup mounted on the chassis. Performance, when added to the high tolerance to misalignment required for a practical EV charging system, necessarily results in circular pads that are large, heavy and expensive. A new pad topology termed a flux pipe is proposed in this paper that overcomes difficulties associated with conventional circular pads. Due to the magnetic structure, the topology has a significantly improved flux path making more efficient and compact IPT charging systems possible.