John T. Boys

Bio: John T. Boys is an academic researcher from University of Auckland. The author has contributed to research in topics: Electromagnetic coil & Maximum power transfer theorem. The author has an hindex of 12, co-authored 14 publications receiving 765 citations.

Tripolar Pad for Inductive Power Transfer Systems for EV Charging

Abstract: A recently proposed magnetic structure called Tripolar Pad (TPP) is investigated as a primary pad in an inductive power transfer battery charging system for electric vehicles. In this paper, a TPP primary is evaluated for 3.3 kW power transfer to both a circular pad and a bipolar pad as secondary pads. A mathematical model is presented to describe the power transfer from the TPP primary to the secondary pads then a control scheme is proposed which exploits the mutual decoupling between the TPP coils to find optimal primary currents. The optimization of the primary currents in the TPP improved the effective coupling factor over traditional topologies, particularly when the secondary was misaligned, and maintained leakage magnetic flux below International Commission on Non-Ionizing Radiation Protection guidelines. The result for the proposed TPP is validated with practical measurements.

Double-Coupled Systems for IPT Roadway Applications

Abstract: Dynamic powering of in-motion electric vehicles (EVs) using inductive power transfer (IPT) can potentially solve many of the problems currently faced by EVs: in particular range, cost, and charging rate. However, there is currently limited research focused on suitable IPT primary supply-side infrastructure for such roadway IPT systems, and most proposed systems so far have limitations that affect their usefulness and/or suitability. This paper presents a new roadway IPT system using a double-coupled system that can largely resolve these limitations. The proposed system introduces an intermediary coupler circuit (ICC) with frequency changing capability between the power supply primary track and each ground transmitter pad/coil arrangement. Individual charging sections on the roadway can be controlled independently using the ICCs and only turned ON when required, and as such minimize unwanted magnetic leakage fields. The proposed system provides isolation between the power supply and all of the ground transmitter pads, and allows the power supply to run at a lower frequency while the power transfer takes place at a higher frequency. The system can also potentially reduce the impact of dynamic EV charging on the electrical grid at the times of traffic congestion. A laboratory scale prototype system has been constructed and tested. The intermediary coupler achieved an efficiency of 92.5% at an output power of 5 kW with full system operability.

Detection of EVs on IPT Highways

Abstract: Electric vehicles (EVs) are quickly gaining widespread interest as attractive alternatives to conventional petrol driven vehicles. If EVs derive some or all of their power from renewable sources, then they can help reduce global dependence on fossil fuels for transportation. Inductive power transfer (IPT) is a method that can transfer power to EVs over an air gap without physical contact. If IPT systems are incorporated into highways, then EVs can be charged dynamically as they travel. This will dramatically increase the range, convenience and safety of EV charging as well as reduce range anxiety and battery bank capacities. One of the major difficulties involves detecting an EV as it travels along the highway. By detecting the approaching EV, the primary power supply can energize the primary IPT coupler buried in the roadway to enable contactless power transfer to the EV. A three coil detection system, which focuses on these sensor coils and which is independent of the specific IPT coupler used, is presented to allow the power supply to detect the approaching EV mounted secondary IPT coupler. The proposed detection method was tested on a laboratory scale prototype and can detect EVs approaching at different speeds, ground clearances, and horizontal misalignments.

Evaluation of Magnetic Pad Sizes and Topologies for Electric Vehicle Charging

Abstract: Inductive power transfer is becoming increasingly popular in stationary electric vehicle charging systems due to improved designs. However, such optimizations are normally performed for matched topologies which are similarly sized, over constant air gaps and without significant misalignment. In a real situation where the primary and secondary pads may not be matched and may be misaligned, pad designs must take into consideration coupling factors, leakage fluxes, pad quality factors, reflected impedance, and size. This paper analyzes the effects which variations in pad sizes, topologies, and displacements in three dimensions has on these parameters. It was found that solenoid pads should not be used as a primary pad due to high leakage fluxes, low native quality factors, and the fact that they are not fully interoperable over the whole desired range of use. Bipolar pad primaries are able to couple to any secondary pad over the entire range of use required and tend to have high native quality factors. Nonpolarized pads tend to have the lowest leakage fluxes but also low coupling. Suggestions on techniques to optimize these pads have also been included.

Analysis of Coplanar Intermediate Coil Structures in Inductive Power Transfer Systems

Abstract: Intermediate couplers have been shown to increase the coupling from primary to secondary pads in inductive power transfer (IPT) systems. This paper investigates embedding a coplanar intermediate coupler coil with the primary coil inside the primary pad to boost the coupling to the secondary pad and improve the efficiency of the system. Several coil designs are simulated and a mathematical model is developed to evaluate the efficiency of parallel–parallel and series–series tuned systems. As shown a coplanar, independently tuned intermediate coupler coil improves the efficiency of a series–series-tuned system since it reduces source losses. However, there appears to be no benefit to having an intermediate coupler with a parallel–parallel-tuned system. Furthermore, boosts in coupling are a result of adding extra current carrying windings to the primary pad and simulations show that operating the system as a traditional two coil IPT system may be simpler and more effective based on tuning topology. An experimental system was constructed to validate the simulations.

Modern Advances in Wireless Power Transfer Systems for Roadway Powered Electric Vehicles

Abstract: Wireless power transfer system (WPTS)-based wireless electric vehicles, classified into roadway-powered electric vehicles (RPEVs) and stationary charging electric vehicles (SCEVs), are in the spotlight as future mainstream transportations. RPEVs are free from serious battery problems such as large, heavy, and expensive battery packs and long charging time because they get power directly from the road while moving. The power transfer capacity, efficiency, lateral tolerance, electromagnetic field, air-gap, size, weight, and cost of the WPTSs have been improved by virtues of innovative semiconductor switches, better coil designs, roadway construction techniques, and higher operating frequency. Recent advances in WPTSs for RPEVs are summarized in this review paper. The fifth- and sixth-generation online electric vehicles, which reduce infrastructure cost for commercialization, and the interoperability between RPEVs and SCEVs are addressed in detail in this paper. Major milestones of the developments of other RPEVs are also summarized. The rest of this paper deals with a few important technical issues such as coil structures, power supply schemes, and segmentation switching techniques of a lumped inductive power transfer system for RPEVs.

Wireless Power Transfer for Vehicular Applications: Overview and Challenges

Abstract: More than a century-old gasoline internal combustion engine is a major contributor to greenhouse gases. Electric vehicles (EVs) have the potential to achieve eco-friendly transportation. However, the major limitation in achieving this vision is the battery technology. It suffers from drawbacks such as high cost, rare material, low energy density, and large weight. The problems related to battery technology can be addressed by dynamically charging the EV while on the move. In-motion charging can reduce the battery storage requirement, which could significantly extend the driving range of an EV. This paper reviews recent advances in stationary and dynamic wireless charging of EVs. A comprehensive review of charging pad, power electronics configurations, compensation networks, controls, and standards is presented.

A Comprehensive Review of Wireless Charging Technologies for Electric Vehicles

Abstract: The profitable commercialization and fast adoption of electrified transportation require fast, economical, and reliable charging infrastructure. This paper provides a comprehensive, state-of-the-art review of all the wireless charging technologies for electric vehicle (EVs), characteristics and standards available in the open literature, as well as sustainable implications and potential safety measures. A comparative overview of conductive charging and wireless charging is followed by a detailed description of static wireless charging, dynamic wireless charging (DWC), and quasi-DWC. Roadblocks, such as coil design of power pads, frequency, power level limitations, misalignment, and potential solutions, are outlined. The standards are then tabulated to deliver a coherent view of the current status, followed by an explanation of the crux of these standards. Necessity and progress in the standardization of wireless charging systems are then deliberated. Vehicle-to-grid application of wireless charging is reviewed followed by an overview of economic analysis, social implications, the effect on sustainability, and safety aspects to evaluate the commercial feasibility of wireless charging. This paper will be highly beneficial to research entities, industry professionals, and investment representatives as a ready reference of the wireless charging system of EVs, with information on important characteristics and standards.

Maximum Energy Efficiency Tracking for Wireless Power Transfer Systems

Abstract: A method for automatic “maximum energy efficiency tracking” operation for wireless power transfer (WPT) systems is presented in this paper. Using the switched-mode converter in the receiver module to emulate the optimal load value, the proposed method follows the maximum energy efficiency operating points of a WPT system by searching for the minimum input power operating point for a given output power. Because the searching process is carried out on the transmitter side, the proposal does not require any wireless communication feedback from the receiver side. The control scheme has been successfully demonstrated in a two-coil system under both weak and strong magnetic coupling conditions. Experimental results are included to confirm its feasibility.