Inductively Coupled Power Transfer Research Articles

Wireless Charging System With a Non-conventional Compensation Topology for Electric Vehicles and Other Applications

The proposed paper presents a complete 500W, universal input, wireless electric vehicle battery charging system using a non- conventional compensation topology, LSPS. An algorithm to compensate Loosely Coupled Inductive Power Transfer (LCIPT) systems with such topology is explained. The design and implementation of each power converter, as well as the coils manufacturing process, is briefly covered. Experimental results are shown to validate the expected system behavior.

Integration of Inductively Coupled Power Transfer and Hybrid Energy Storage System: A Multiport Power Electronics Interface for Battery-Powered Electric Vehicles

Detailed in this paper is a multiport power electronics interface which serves as an energy router for on-board electric and plug-in hybrid electric vehicles with inductively coupled power transfer (ICPT) and hybrid energy storage systems (HESS). The existing body of literature on HESSs lacks a unified controller and modular, flexible structure as well as integration of ICPT. In battery/ultracapacitor systems, this leads to piece-meal control of sources resulting in battery currents which are not fully decoupled from high-frequency/high-magnitude current and ultra-capacitor (UC) state of charge (SoC) not being properly controlled. A central controller is proposed in this paper which completely decouples the battery from both high-frequency and high-magnitude current, controls the SoC of the UCs, and models the SoC of the UCs in the stability analysis of the system. This system is particularly useful for online charging of HEVs in highway-type applications where ICPT pulse charging will be present. Solving the challenges of pulse charging will bring ICPT technology one step closer to widespread integration which has the potential to greatly reduce societies' dependence on fossil fuel. Simulation and experimental results verify the feasibility of the proposed techniques.

Frequency, Impedance Characteristics and HF Converters of Two-Coil and Four-Coil Wireless Power Transfer

Magnetically coupled wireless power transfer (WPT) can be roughly divided into two kinds of inductively coupled and strongly coupled magnetic resonances. In this paper, the frequency characteristics, impedance characteristics and high frequency (HF) converters of two-coil and four-coil magnetically coupled WPT are outlined between inductively coupled power transfer (ICPT) and resonant coupling WPT. First, the frequency bifurcation in ICPT and frequency splitting in resonant coupling WPT are analyzed, and the natural similarities are explained, which have not been pointed out before. Second, the differences of the conventional two-coil (often used in ICPT) and four-coil WPT are analyzed by their input impedance characteristics. The results show that the two-coil WPT is appropriate for short-range and the four-coil WPT suitable for mid-range applications. In the end, as one of the most important parts of magnetically coupled WPT systems, HF converters used in WPT systems are summarized and a new soft-switched converter is put forward, which has 70% efficiency though it is not precisely designed.

Analysis and Design of Bi-Directional PowerRegulator with wireless Power TransferTechnology for Electric Vehicles

Wireless charging has the power to greatly increase the convenience and accessibility of electric vehicles for charging. Wireless charging involves transferring power from the electric grid to a battery without the use of wires, cords or plugs. Electric vehicles not only draw power from the grid but also can supply surplus energy to grid or home when power consumption peaks or power outage. This is done with the help of bi-directional wireless power transfer technology. A wireless electric vehicle charging system based on inductively coupled power transfer (ICPT) technology is presented in this project. A simulation system is built in the Simulink, and the feasibility of the system is proved by simulation results.

Detection of EVs on IPT Highways

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.

Determining the Physical Size of Inductive Couplers for IPT EV Systems

Due to increasing environmental concerns and decreasing fossil fuel supplies, electric vehicles (EVs) are fast becoming attractive alternatives to conventional fossil-fuel driven vehicles. Inductive power transfer (IPT) is a method that can be used to transfer power to EVs over an air-gap and can dramatically increase the range, convenience, and safety of EV battery charging. One of the major difficulties is determining the physical sizes of the primary IPT coupler, buried in the roadway, and the EV mounted secondary coupler. This is mainly due to the variation in vehicle classes and charging locations that may be encountered. This paper seeks to determine if suitably sized couplers can be selected, which can realize all these demands. A recently proposed EV charging coupler, known as the Double-D (DD), which has been shown to provide the best power to size ratio over typical expected air gaps is selected. As such a method to select the best design from eight approximately square DD couplers ranging from 300 to 1000 mm in length to meet the challenge of delivering high power over large air-gaps is presented. The performance of these couplers, or power pads, is simulated and the results can be used to select couplers for EV charging systems. A practical design example is presented involving the IPT charging of sedans and SUVs in multiple practical charging locations. The proposed pad sizes and systems are capable of transferring 10 kW to the EVs for realistic horizontal misalignments (±200 mm) and air-gaps (100-400 mm).

Theory of Image Impedance Matching for Inductively Coupled Power Transfer Systems

The optimum design of an inductively coupled power transfer system is accomplished by applying the Roberts's theory on conjugate image impedance. The input and output ports' impedance and the loading capacitances for maximum power transfer are obtained as functions of the self-inductances, the mutual inductance, the copper losses, and the iron loss, which are used to define the figure-of-merit of the system. It is found that the loading capacitances necessarily satisfy the resonance conditions individually in the input and output circuits. The capacitors may be connected in series or in parallel. The equivalent transform formulas between the series and parallel topologies are given for the capacitances and for the port impedances. The port impedance in the series (parallel) topology is proportional (approximately inversely proportional) to the inductive coupling coefficient. The image impedances of the lossless symmetric systems are real or pure imaginary depending on the frequency, and the image impedance patterns are classified as “Hill”, “Valley”, and “Waterfall". The reactance network approach for such lossless systems gives in-depth insight into the system behaviors and facilitates the practical design.

Computational Finite Element Software Assisted Development of a 3D Inductively Coupled Power Transfer System

To date inductively coupled power transfer (ICPT) systems have already found many practical applications including battery charging pads. In fact, current charging platforms tend to largely support only one- or two-dimensional planar movement in load. This paper proposes a new concept of extending the aspect ratios of the operating power transfer volume of ICPT systems to support arbitrary three dimensional load movements with respect to the primary coils. This is done by use of modern finite element method analysis software to propose the primary and secondary magnetic structures of such an ICPT system. Firstly, two primary magnetic structures are proposed based on contrasting modes of operation and different field directions. This includes a single-phase and multi-phase current model. Next, a secondary magnetic structure is customized to be compatible with both primary structures. The resulting system is shown to produce a 3D power transfer volume for battery cell charging applications.

Infrastructure Cost Issues Related to Inductively Coupled Power Transfer for Electric Vehicles

The electrification of vehicles has been accelerated over the last few years due to tighter emission regulations, volatile fuel prices, and progress in standardization as well as improvement of battery technologies. Key hurdles of electric vehicles (EV) to gain a larger share in the automotive market are the cost of the energy storage system (ESS) and the density of the EV charging infrastructure. The achievable range of an EV or full electric driving of a plugin hybrid electric vehicle (PHEV) is limited by its battery capacity. The time to recharge the battery is related to the power level of charging as well as allowable charging parameters to protect the battery life. In order to overcome the constraints of limited range of EVs (all electric driving) as well as the cost of ESS, inductively coupled power transfer (ICPT) is an interesting technology path to be considered, in particular if applied as opportunity (stop-and-go) or in-motion charging (also called dynamic wireless charging or move and charge). In-motion wireless charging could lead to significant reductions of the vehicle-related cost of electrification but this comes with the price of an infrastructure that needs to be built and maintained. In order to design the ICPT infrastructure and calculate the cost of construction and operation, certain assumptions have to be made with respect to the vehicle specifications, the specification of the charging system itself and the cost of integration into the existing road infrastructure. The objective of this paper is to provide a thorough analysis of the cost associated with the implementation of a dynamic ICPT infrastructure to support the operation of electrified vehicles and to present transportation agencies a business model that can provide a starting point for the development of a new EV infrastructure.

Design and analysis of an underwater inductive coupling power transfer system for autonomous underwater vehicle docking applications

We develop a new kind of underwater inductive coupling power transfer (ICPT) system to evaluate wireless power transfer in autonomous underwater vehicle (AUV) docking applications. Parameters that determine the performance of the system are systematically analyzed through mathematical methods. A circuit simulation model and a finite element analysis (FEA) simulation model are developed to study the power losses of the system, including copper loss in coils, semiconductor loss in circuits, and eddy current loss in transmission media. The characteristics of the power losses can provide guidelines to improve the efficiency of ICPT systems. Calculation results and simulation results are validated by relevant experiments of the prototype system. The output power of the prototype system is up to 45 W and the efficiency is up to 0.84. The preliminary results indicate that the efficiency will increase as the transmission power is raised by increasing the input voltage. When the output power reaches 500 W, the efficiency is expected to exceed 0.94. The efficiency can be further improved by choosing proper semiconductors and coils. The analysis methods prove effective in predicting the performance of similar ICPT systems and should be useful in designing new systems.

Research of the Constant Current Characteristic of Symmetric AC-AC Inductive Coupled Power Transfer System

Research of the Constant Current Characteristic of Symmetric AC-AC Inductive Coupled Power Transfer System

Design and Implementation of Inductive Coupling Power Transfer Device Based on Structural Parameters Analysis

With the rapid development of power electronics technology, the applications of inductively coupled power transfer make the wireless power transmission reality. In order to explore the practical application in the field of ICPT, we analysis the core component of a loosely coupled transformer of ICPT and design it. We make a model and simulate the core magnetic field distribution of the loosely coupled transformer with ANSYS and we select the appropriate core structure. We produce loosely coupled transformer through the analysis of loosely coupled transformer performance parameters affecting factors. Research on the basis of loosely coupled transformer, we build ICPT experimental device and we also analysis the transmission efficiency by the gap of the system with actual measurement.

Optimisation of an inductive power transfer structure

This paper presents the multi-objective optimisation of an Inductive Coupled Power Transfer (ICPT) device. A setup as complicated as the one at hand in this paper is extremely hard to model analytically. To acquire some knowledge about the influence of the geometric factors, a sensitivity analysis is first performed using design of experiment (DoE) and finite-element modelling (FEM). It allows validating that the choice of the free factors is relevant. This being done, the optimisation itself is performed using a genetic algorithm (GA), with two objectives and a strict functioning constraint.

$\mu$-Synthesis for Frequency Uncertainty of the ICPT System

A μ-controller is designed based on the structured singular value with regard to the frequency uncertainty of a real inductively coupled power transfer (ICPT) system. Due to system-parameter variations (such as system load) and nonlinear features of ICPT systems, the operating frequency will be perturbed accordingly. Uncertainty in the operating frequency will contribute to electromagnetic interference and power losses, and even instability of ICPT systems. To fulfill a robust stability and robust performance (RSRP) design, a generalized state-space averaging model for a nominal ICPT system is established by developing the equivalent circuit equations and expanding the related circuit variables as the Fourier series. A linear fractional transformation of this nominal model and its uncertainty is discussed to generate a standard configuration for μ-synthesis. The D-K iteration method is proposed for the “optimal” RSRP design. Computer simulation and a practical experiment are conducted to verify the RSRP of the μ-synthesis control system to ensure that the μ-synthesis algorithm is effective for ICPT systems.

Robust control for an uncertain LCL resonant ICPT system using LMI method

Frequency drift has considerable adverse effects on the inductively coupled power transfer (ICPT) system such as decrease of transmission power and distance, EMC interference, system detuning and performance deterioration, and deviated operation from system design requirements endangering the stability so that robust control of ICPT system remains an open applied research problem. This article presents a relevant uncertain model for the LCL resonant ICPT system first via the generalized state-space averaging and the LFT methods, and then a solution to H∞ controller synthesis by making use of the LMI method. The control design is first tested by computer simulation and thereafter verified by means of physical experiments. The results show that by applying the proposed H∞ synthesis controller the overall system has achieved both predetermined robustness with respect to the norm-bounded load and frequency uncertainties and dynamically tracking the voltage references according to the actual power demands.

Theoretical Analysis of Power Transfer Performance of Primary and Secondary Compensation Topology of Inductive Coupled Power Transfer System

Inductive coupled power transfer system is based on the principle of electromagnetic induction to transfer power from the primary side to the secondary side of a loosely coupled transformer, which can transfer electricity wirelessly. The loosely coupled transformer has large leakage inductance, which reduces the power transfer efficiency. In order to reduce the leakage inductance, a capacitance is used at the primary side and secondary side of a loosely coupled transformer, which can increase the power transfer efficiency. For four different compensation structures, this paper analyses the coupling coefficient and the secondary quality factor’s influence on the voltage gain, current gain and transfer efficiency, and also compares different compensation structures

A Resonant Frequency Control Strategy for Contactless Power Transfer Systems

In an inductively coupled power transfer (ICPT) system, a primary capacitance is usually used to minimize the VA rating of power supply, and a secondary capacitance is adopted to maximize the power transfer. The changes of the secondary capacitance because of environmental temperature or other factors will alter the resonant frequency of the secondary side, and thus the power transfer capability is varied. In this study, the power transfer capability of ICPT systems is investigated in detail when the secondary capacitance changes. A resonant frequency control strategy is suggested to keep the system operation frequency to follow closely the secondary resonant frequency when the secondary capacitance varies. This new strategy is based on the synergic action of the system operation frequency and the primary capacitance. The performance of three frequency control methods, that is the resonant frequency control, the traditional variable frequency control, and the fixed frequency control, are compared when the secondary capacitance varies. A distinguish feature of a resonant frequency control is that the power transfer is an approximately linear function of the secondary capacitance. This linear characteristics facilitate a voltage control strategy being used to keep the load power unchanging when the secondary capacitance varies. A traditional viewpoint in an ICPT system is that maximizing of output power is achieved when the system operation frequency is equal to the secondary resonant frequency. Numerical simulations show that the power output by a resonant frequency control do not always dominate the power output from other two frequency control methods. This phenomenon suggests that above traditional viewpoint is a misconception, and should be reexamined. The power transfer capability of ICPT systems is an intricate function of the operational frequency, and thus resonant operations of the secondary side do not always guarantee maximizing the power transfer. A suitable control mechanism, such as the resonant frequency control, the variable frequency control, or the fixed frequency control, should be designed carefully according to the practical engineering requirement when the secondary capacitance varies.

Optimal Design of ICPT Systems Applied to Electric Vehicle Battery Charge

Although the use of inductively coupled power transfer (ICPT) systems for electric vehicle battery charge presents numerous advantages, a detailed design method cannot be found in the literature. This paper shows the steps to follow in the optimized design of an ICPT system and the results obtained in their application to the four most common compensation topologies, pointing out the best one in terms of minimum copper mass and proper stability conditions. A new design factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> is proposed to select the optimum configuration for each topology. Finally, the theoretical results are validated on a 2-kW prototype with a 15-cm air gap between coils.

Design of a high frequency Inductively Coupled Power Transfer system for electric vehicle battery charge

The development of a high autonomy purely electrical public mean of transportation is not currently viable because the required energy implies a very high battery weight. However, this weight would be significantly reduced if these batteries could be charged at the bus stops along the route, for instance using a contact-less power transfer system. An ICPT (Inductive Coupling Power Transfer) system with a large air gap has been developed and built for an electric vehicle battery charger. The practical sizing, the best compensation topology and the operational frequency have been studied in order to obtain maximum efficiency. The study has been focused on defining the prototype implementation process, validating the theoretical results and analyzing the influence of frequency deviation with respect to the resonant frequency and the effect of gap variation and misalignment in the behaviour of the system.

Inductive Charging of Ultracapacitor Electric Bus

Many public transit agencies are exploring ways in which alternative fuels can be utilized to reduce our nation’s dependency on imported oil and to avoid the environmental impacts associated with the combustion of petroleum products. Of all the alternative fuel options, electricity is among the most desirable in terms of affordability, availability, security, and sustainability. Unfortunately, limitations in battery technology result in electric vehicle operating ranges that are much lower than those of internal combustion-powered vehicles. Although opportunity charging is one strategy for increasing the driving range of electric buses by means of a series of brief recharges during normally scheduled midday layovers, it has yet to be embraced by the transit industry, in part because of the difficulties involved in having drivers connect and disconnect the bus from the charger at regular intervals throughout the day. Roadway-mounted inductively-coupled power transfer systems effectively remove this constraint by automating the charge process, thereby obviating the need for driver intervention. Ultracapacitor energy storage systems offer advantages over battery systems for such applications.