Grant A. Covic

Design considerations for a contactless electric vehicle battery charger

This paper overviews theoretical and practical design issues related to inductive power transfer systems and verifies the developed theory using a practical electric vehicle battery charger. The design focuses on the necessary approaches to ensure power transfer over the complete operating range of the system. As such, a new approach to the design of the primary resonant circuit is proposed, whereby deviations from design expectations due to phase or frequency shift are minimized. Of particular interest are systems that are neither loosely nor tightly coupled. The developed solution depends on the selected primary and secondary resonant topologies, the magnetic coupling coefficient, and the secondary quality factor.

Power transfer capability and bifurcation phenomena of loosely coupled inductive power transfer systems

Loosely coupled inductive power transfer (LCIPT) systems are designed to deliver power efficiently from a stationary primary source to one or more movable secondary loads over relatively large air gaps via magnetic coupling. In this paper, a general approach is presented to identify the power transfer capability and bifurcation phenomena (multiple operating modes) for such systems. This is achieved using a high order mathematical model consisting of both primary and secondary resonant circuits. The primary compensation is deliberately designed to make the primary zero phase angle frequency equal the secondary resonant frequency to achieve maximum power with minimum VA rating of the supply. A contactless electric vehicle battery charger was used to validate the theory by comparing the measured and calculated operational frequency and power transfer. For bifurcation-free operation, the power transfer capability and controllability are assured by following the proposed bifurcation criteria. Where controllable operation within the bifurcation region is achievable, a significant increase in power is possible.

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.

Design of loosely coupled inductive power transfer systems

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.

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

A design methodology for loosely coupled inductive power transfer systems is proposed. Such systems are used for noncontact power transfer, often over large airgaps to moving loads. Due to the large leakage inductances that result, compensation is usually necessary to achieve the required power transfer capability. The level of compensation, as well as possible compensation topologies, are discussed in the paper. Special attention is paid to the tradeoffs involved during the design process.

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.