Inductive Power Transfer Coils Research Articles

Optimization of Circular Coils with Ferrite Boxes for Enhanced Efficiency in Wireless Power Transfer for Electric Vehicles

This study responds to global climate concerns by addressing the shift towards sustainable transportation, particularly electric vehicles. Focusing on wireless power transfer to overcome charging infrastructure challenges, the research optimizes circular coils for inductive power transfer in electric cars. Utilizing ferrite cores to enhance performance, the study employs ANSYS Electronics Suite R2-202 and the finite element method to analyze circular coils, exploring variations in turns, inner radius, air gap, and misalignment's impact on the coupling coefficient. Introducing ferrite plan cores and boxes, the research finds that ferrite boxes improve coupling efficiency by 50% and electromagnetic field strength by 300%, concentrating the field toward the center. An inequivalent design, enlarging the primary coil, demonstrates significant enhancements, achieving a coupling coefficient increase of 0.183447 and an electromagnetic field rise of 0.00040 Tesla. Equivalent coils with ferrite boxes meet a 95% efficiency goal with a strong, narrowed field at a lower cost, while inequivalent coils excel in strengthening and centralizing the field, enhancing misalignment tolerance in distinctive ways.

A Super-Resonant Frequency Control for Handshaking of an Inductive Power Transfer System With Adjacent Units

In inductive power transfer (IPT) applications where multiple IPT units can appear closely, the wrong pairing of one transmitter (Tx) unit and receiver (Rx) unit can happen and may cause damages. For example, for automated guided vehicle and electric vehicle applications, one IPT charger may find multiple nearby Rx units through radio frequency modules. If the charger wrongly pairs with an Rx unit in an adjacent lane, the charger will attempt to charge the correct Rx unit using the information from the adjacent Rx unit, which is a faulty operation. In this letter, IPT coils are used to transmit handshaking information, which inherently avoids adjacent Tx/Rx units. During handshaking, only small ac currents would occur even with a high dc input. When the Tx and Rx are far away, system currents remain small. Hence, the approach is a safe solution to assist pairing. Experimental results have been provided for verification.

A Review of Wireless Pavement System Based on the Inductive Power Transfer in Electric Vehicles

The proliferation of electric vehicles (EVs) hinges upon the availability of robust and efficient charging infrastructure, notably encompassing swift and convenient solutions. Among these, dynamic wireless charging systems have garnered substantial attention for their potential to revolutionize EV charging experiences. Inductive power transfer (IPT) systems, in particular, exhibit a promising avenue, enabling seamless wireless charging through integrated pavements for EVs. This review engages in an in-depth exploration of pertinent parameters that influence the inductivity and conductivity performance of pavements, alongside the assessment of potential damage inflicted by IPT pads. Moreover, the study delves into the realm of additive materials as a strategic approach to augment conductivity and pavement performance. In essence, the review consolidates a diverse array of studies that scrutinize IPT pad materials, coil dimensions, pavement characteristics (both static and dynamic), and adhesive properties. These studies collectively illuminate the intricate dynamics of power transfer to EVs while considering potential repercussions on pavement integrity. Furthermore, the review sheds light on the efficacy of various additive materials, including metal and nanocomposite additives with an SBS base, in amplifying both conductivity and pavement performance. The culmination of these findings underscores the pivotal role of geometry optimization for IPT pads and the strategic adaptation of aggregate and bitumen characteristics to unlock enhanced performance within wireless pavements.

Design and Characterization of PCB Spiral Coils for Inductive Power Transfer in Medium-Voltage Applications

Coil design and operating frequency are key factors impacting the efficiency of the inductive power transfer system. This article presents the modeling of printed circuit board spiral coils, design optimization and analysis on coil geometry, and operating frequency for medium-voltage (MV) applications, such as auxiliary power supplies for MV converters. Analytic model considering the geometric distribution of the magnetic field is proposed to calculate with high accuracy equivalent electrical parameters of coils. For a defined design space and constraints, a large number of coils are designed to determine their performances and select optimal coil geometries. Selected coil designs are prototyped and experimentally verified under design-specific conditions. In addition, further characterization is performed considering variations of several parameters that can be encountered in practice.

A Current-Sharing Compensation Method for High-Power-Medium-Frequency Coils Composed of Multiple Branches Connected in Parallel

In inductive power transfer (IPT) systems, the coils with paralleled multiple branches are commonly used in high power applications where the frequency range is between 20 and 90 kHz. The traditional compensation method takes multiple branches as a whole and the compensation capacitors are connected outside the coils, which suffers from current unbalance among multiple branches, but currently few researchers analyze it. Therefore, this article illustrates the current-unbalance mechanism and proposes a current-sharing compensation method for IPT coils. The current-unbalance characteristics of coils with paralleled multiple branches are illustrated to prove the current-sharing necessity. Then, based on the relation between the impedance of branch and current unbalance, a compensation capacitor with a specially designed value is connected in each branch, so that the current unbalance can be suppressed by the increased branch impedance. Besides, the cost, volume, and weight of IPT systems remain unchanged approximately. Finally, a 30-kW IPT prototype is built up to verify the availability of the proposed method, and the currents and temperatures of multiple branches are equally distributed within wide power range with this method.

2-D Thin Coil Designs of IPT for Wireless Charging of Automated Guided Vehicles

As the automated guided vehicles (AGVs) play an important role in automated logistics systems, the wireless power transfer (WPT) technologies become a viable solution to provide the AGV with the automatic power charging service. In order to install the WPT systems to the small confined space in the AGV, a 2-D thin coil design is necessary for the receiver (Rx) system installed in the AGV. To greatly reduce the thickness of the Rx coil, including resonant capacitors, an ac/dc rectifier, and dc-link capacitors, an 2-D coil design for a minimum core loss is newly proposed in this article. Based on a finite-element-method (FEM) 3-D simulation analysis, various coil structures have been comparatively evaluated to find the most appropriate core structure. Furthermore, to obtain the highest coil efficiency at nominal operating condition, the appropriate number of turns design is established. Thus, according to the coil design guideline of the proposed inductive power transfer (IPT) system, the appropriate number of turns for transmitter (Tx) and Rx coils <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{\mathrm {1,op}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{\mathrm {2,op}}$ </tex-math></inline-formula> can be appropriately selected for the high efficient operation of the IPT coils. The 2.5-kW prototypes of the IPT systems for wireless charging of AGV were fabricated and verified by simulations and experiments. The results showed that the total thickness of the coil sets including all the components is 32.0 mm for the Rx coil. The measured maximum coil efficiency for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{L} =2.5$ </tex-math></inline-formula> kW at 40-mm coil distance was 98.9% by the proposed IPT coil design procedure. The measured temperatures at the ferrite core and coil for the Rx coil were managed below 53.3 °C and 59.3 °C during 2.5-kW wireless charging, respectively, under a 10-min charging and 20-min AGV operation cycle, which provides the thermal-stable operation of the proposed IPT systems.

Computational Design for Digitally Fabricated 3D Inductive Power Transfer Coils

Abstract The geometric shapes and the relative position of coils influence the performance of a three-dimensional (3D) inductive power transfer system. In this paper, we propose a coil design method for specifying the positions and the 3D shapes of a pair of coils to transmit the desired power. Given region of interests (ROIs) for designing the transmitter and the receiver coils on two surfaces, the transmitter coil is generated around the center of its ROI. The center of the receiver coil is estimated as a random seed position in the corresponding 3D surface. At this position, we use the heatmap method with electromagnetic constraints to iteratively extend the coil until the desired power can be transferred via the set of coils. In each step, the shape of the extension, i.e., a new turn of the receiver coil, is found as a spiral curve based on the convex hulls of the 2D projected adjacent turns along their normal direction. Then, the optimal position of the receiver coil is found by maximizing the efficiency of the system. In the next step, the position and the shape of the transmitter coil are optimized based on the fixed receiver coil using the same method. This optimization process iterates until an optimum is reached. Simulations and experiments with digitally fabricated prototypes were conducted and the effectiveness of the proposed 3D coil design method was verified.

Segmented IPT Coil Design for Continuous Multiple Charging of an Electrified Monorail System

Inductive power transfer (IPT) systems based on segmented transmitter (Tx) coils are newly proposed in this article. These IPT systems can deliver wireless power to multiple transport robots in an electrified monorail system (EMS) for continuous transportation missions. Considering the one-dimensional long-line driving characteristics of the transport robots having receiver (Rx) systems, a segmented Tx coil structure is introduced so that flexible Tx installation, easily Tx coil fabrication, and insensitive IPT characteristics are possible. In this case, in order to remove the magnetic dead-zones at the adjacent sections between the adjacent Tx coils, folded Tx coils, and an optimally sized Rx coil are applied to the proposed IPT system in this article. Thus, continuous wireless powering to multiple transport robots in the EMS and flexible extending of the Tx length are possible by the proposed IPT systems. For the soft-switching operations of the proposed IPT systems, a gyrator-based static circuit modeling is presented in order to select an appropriate resonant capacitance. By the proposed gyrator-based circuit analysis, it is found that high efficiency Tx circuit operation can be achieved, regardless of the number of Rx and the load conditions. The proposed segmented multiple Tx systems and the 30 W Rx systems for the transport robots were fabricated and verified by experiments for various operating scenarios. Compared with the conventional 2-m-long Tx coil having 69.1% dc power efficiency, the two-segmented 1-m-long Tx coil systems have no powering dead zone and achieved 74.2% dc power efficiency for one 30 W Rx system. As a result, the proposed two segmented 1-m-long Tx systems have 5.1% higher dc efficiency than the conventional 2-m-long Tx coil under the 2-m-long driving route in EMS application.

Common Mode Noise Analysis for Inductive Power Transfer System Based on Distributed Stray Capacitance Model

This article reveals the significant stray capacitances in inductive power transfer (IPT) coil, and offers two methods for modeling the stray capacitance effect: concentrated model and distributed model. Both analytic formulas and FEM simulation are introduced to estimate the value of parasitic capacitances, and experimental measurements on an 11 kW IPT coil prototype are conducted to verify the correctness of both methods. The common-mode noise propagation circuit of the IPT system is derived and simulated based on these two models. The results show that parasitic capacitance between Litz wire winding and shielding metal on the transmitter side plays a dominant role in CM noise propagation and the distributed model has higher fidelity because of its asymmetric structure. Besides, to mitigate conductive CM noise, an EMI filter, and HF isolation transformer are introduced. Finally, the conductive EMI tests are performed in an 11kW IPT prototype. The experimental results validate the accuracy of the proposed CM noise model with stray capacitances of the IPT coil. And the combination of EMI filter and HF isolation transformer can suppress CM noise greatly and render the CM noise spectrum below the CISPR 32 Class-B limit.

Self and Mutual Inductance Behavioral Modeling of Square-Shaped IPT Coils With Air Gap and Ferrite Core Plates

The design and optimization of coils for Inductive Power Transfer (IPT) systems is an iterative process conducted in Finite Element (FE) tools that takes a lot of time and computational resources. In order to overcome such limitations in the design process, new empirical equations for the evaluation of the self-inductance and mutual inductance values are proposed in this work. By means of a multi-objective genetic programming algorithm, the self-inductance, the mutual inductance and the coupling factor values obtained from FE simulations of IPT link are accounted by analytical equations, based on the geometric parameters defining the IPT link. The behavioral modeling results are compared with both FE-based and experimental results, showing a good accuracy.

New Structure Design of Ferrite Cores for Wireless Electric Vehicle Charging by Machine Learning

In this article, a machine learning algorithm is applied for the first time in inductive power transfer (IPT) to find a ferrite core structure with high magnetic coupling between transmitting (Tx) and receiving (Rx) coils for an electric vehicle (EV) wireless charging system. Since formula-based theoretical design is not available due to the nonlinear magnetic field distortion stemming from the presence of the ferrite core in an IPT system, the proposed core structure design has been achieved through finite-element analysis simulation-based data learning. The proposed design methods are so general that they can be applied to any conventional IPT coil design. Furthermore, it can optimize the core structures for high coupling coefficient, mutual inductance, desired magnetic flux density in the specific area, etc. By training only 0.011% data out of the total possible cases, it is verified by simulation and experiment that the ferrite core structure obtained by the proposed method has a mutual inductance that is 0.6% higher than that of the conventional design level in the case of 15 cm distance between the Tx and Rx coils, even though the volume of the ferrite cores are reduced to 90%. Also, a prototype 3.0 kW stationary EV wireless charging system was implemented and showed fairly better performance than a conventional case.

Optimal Number of Turns Design of the IPT Coils for Laptop Wireless Charging

The coil design of the inductive power transfer (IPT) for a transmitter (Tx) and receiver (Rx) is crucial to determine the performance of the IPT. Considering core loss and copper loss of the Tx and Rx coils, which are major loss terms of the whole IPT system, determination of the winding turns for the Tx and Rx coils becomes a key factor for maximum power transfer design of the IPT coils. In this paper, an optimal turns design of IPT coils for laptop wireless charging applications with a maximum power transfer efficiency is proposed. Under a specific design requirement of IPT, optimal turns of the Tx and Rx coils N1,op and N2,op can be determined by the proposed IPT coil design procedure with a finite-element-method (FEM) based simulation analysis. From the results of the coil design by the proposed IPT coil design methodology, N1,op and N2,op for maximum power efficiency, and input DC voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> for the target load power can be found by the proposed coil design procedure. The 40W prototypes of the two symmetry and asymmetry IPT coils for laptop wireless charging were fabricated, and verified by simulation and experiments. To separately verify the core and copper loss of the IPT coils, a resistance model and Steinmetz equation-based methods were comparatively evaluated, and it was found that they matched well at a core temperature condition of below 40oC. The results showed that the total weight and the thickness of the Tx and Rx coils as well as the maximum power efficiencies of 95.1% and 96.8% for the symmetry and asymmetry cases were obtained by the proposed IPT coil design procedure, which becomes a practical solution for the laptop wireless charging coil design.

Experimental Comparison of Designed Inductance Coils for Wireless Power Transfer

Abstract The paper is devoted to the comparison of different types and different values of coils for inductive power transfer in the classical circuit. This topic is relevant with the growing demand and interest in wireless chargers and the diversity of inductance coils for wireless power transfer. The main geometric parameters affecting the coil efficiency are determined. For experimental verification the classical scheme for wireless power transfer is used based on a full-bridge inverter. Different coils at different distance between them, lateral misalignment and load resistance changed are tested. It is determined that single-layer coils have better transmit-receive efficiency than double-layer ones, especially with series-series compensation topology. The application of two-layer coils is recommended in case of high input current. The investigated samples have efficiency at the level of industrial standards. The design approach can be used for any level of power and application, including wireless charging of electric vehicle batteries.

Hybrid IPT system with natural CC–CV output characteristics for EVs battery charging applications

To charge the battery of electric vehicles (EVs), inductive power transfer (IPT) system has been considered to be more appropriate than traditional plug-in system especially for its security and convenience. This study proposes a hybrid IPT system for EVs charging applications adopting one transmitter coil with series compensation and two receiver coils with series compensation and LCL compensation. With the help of the two receiver coils and proper parameters design, the proposed system can naturally obtain constant current (CC) and constant voltage (CV) outputs and the maximum output power can be naturally limited which can prevent the system from possible overload. Therefore, the reliability of the proposed system is increased. Since the mode switching process can be automatically realised according to the value of battery equivalent load without extra control strategy and circuit, the fixed-frequency control can be used. Therefore, not only zero phase angle condition, but also the soft switching can be achieved. The theoretical analysis is presented with the design process of the IPT coils and resonance parameters for required battery charging profile. The performance of the system is verified by a 3.3 kW experimental prototype. The experimental results coincide well with the theoretical analysis.

Assessment of Exposure to Electric Vehicle Inductive Power Transfer Systems: Experimental Measurements and Numerical Dosimetry

High-power inductive power transfer (IPT) systems for charging light and heavy electric vehicles pose safety concerns if they are installed in uncontrolled environments. Within the framework of the European Project EMPIR-16ENG08 MICEV, a wide experimental and numerical study was conducted to assess the exposure of the general public to IPT stray magnetic fields for two different exposure scenarios: (1) for an IPT model system derived from the SAE J2954 standard operating at 85 kHz for a light electric vehicle coupled with the model of a realistic car-body model; and (2) for an IPT model system with a maximum rated power of 50 kW at 27.8 kHz for a real minibus that was reproduced with some simplifications in two different 3D finite element method (FEM) simulation tools (Opera 3D and CST software). An ad hoc measurement survey was carried out at the minibus charging station to validate the simulations of the real bus station for both aligned and misaligned IPT coils. Based on this preliminary study, a safety factor was chosen to ensure a conservative dosimetric analysis with respect to the model approximations. As highlighted in this study, the vehicle-body serves as an efficient screen to reduce the magnetic field by at least three orders of magnitude close to the coils. By applying FEM, computed spatial distribution to the Sim4Life software, the exposure of three Virtual Population human anatomical phantoms (one adult, one child, and a newborn) was assessed. The three phantoms were placed in different postures and locations for both exposure scenarios. The basic restriction limits, established by the current guidelines, were never exceeded within the vehicles; however, the basic restrictions were exceeded when an adult crouched outside the minibus, i.e., near the coils, or when a newborn was placed in the same location. Borderline values were observed in the light car. In the case of the bus, limits coming from the Institute of Electrical and Electronics Engineers (IEEE) guidelines are never exceeded, while basic restrictions coming from the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines are exceeded up to 12% for an adult and up to 38% for a newborn. This paper presents novel dosimetric data generated in an IPT system for heavy vehicles and confirms some of the literature data on light vehicles.

Equivalent Conductor Layer for Fast 3-D Finite Element Simulations of Inductive Power Transfer Coils

In this article, a method to replace conductors, in one or multiple layers, by an equivalent layer with homogeneous current distribution is proposed to allow complex 3-D finite element simulations. This equivalent layer needs a coarser mesh, then the simulations are accelerated. The electromagnetic properties of this equivalent layer will be defined to match skin and proximity losses of actual round and Litz-wire conductors. Analytical and empirical equations to obtain these parameters will be provided and the method is validated in several inductive power transfer coils with three dimensional geometries.

High $Q$ Coil Measurement for Inductive Power Transfer

A system for the measurement of quality factors, self-inductances, and interturn capacitances of inductive power transfer coils, in the frequency range of 1–20 MHz, is demonstrated. Coil quality factor in excess of 1000 is measured at megahertz frequencies, beyond the capabilities of commercial impedance analyzers. The method used is to measure the transmission bandwidth of the coil under test while under weak magnetic coupling, incorporating measures to reduce common-mode coupling. The measurement system is verified by comparison with electromagnetic simulation and by modeling. The system model shows robustness to system configuration and the potential to measure coils with $Q$ in excess of 10 000.

Comprehensive Evaluation of Rectangular and Double-D Coil Geometry for 50 kW/85 kHz IPT System

In this paper, the influence of the inductive power transfer (IPT) coil geometry on the performance factors efficiency, power density, and stray field is studied for a public transport electric vehicle battery charging system. IPT coil geometries with rectangular winding and with double-D winding are compared based on the Pareto fronts obtained from a multi-objective optimization. In order to study the effect of the winding layout experimentally, two full-scale 50 kW/85 kHz hardware prototypes with the same outer coil dimensions ( $410\times 760\times 60$ mm3) and ferrite core structure are constructed. For both the prototypes, the measured dc–dc efficiency is approximately 95.5% at 50 kW with a 160 mm air gap and ideally positioned coils, which confirms the calculations. The positioning tolerance of the double-D prototype is inferior, because with coil misalignment the efficiency decays faster than for the rectangular winding prototype. Flux density measurements show that both the prototypes fulfill the ICNIRP 2010 standard at 800 mm lateral distance from the coil center. However, the measured magnetic stray field is a factor of two lower for the double-D prototype, which is a key advantage in high-power applications.

Multi-Objective Optimization of 50 kW/85 kHz IPT System for Public Transport

Inductive power transfer (IPT) is an attractive solution for the automated battery charging of public transport electric vehicles (EVs) with low maintenance requirements. This paper presents the design of a 50 kW/85 kHz contactless EV charger, with a focus on the IPT transmitter and receiver coils. The multi-objective magnetics optimization reveals the Pareto tradeoffs and performance limitations in terms of high efficiency, high power density, and low stray field for high-power IPT systems without moving mechanical parts. A full-scale hardware prototype is realized and experimentally investigated. The dc-dc conversion efficiency, including all the power electronics stages, is measured as 95.8% at 50 kW power transfer across an air gap of 160 mm (coil dimensions $410\times 760\times 60$ mm3). With 150 mm coil misalignment in the worst case direction, the dc-dc efficiency drops to 92%. The measurements of the magnetic stray field show compliance with ICNIRP 2010 at 800 mm distance from the IPT coil center.

Electromagnetic field patterns and energy flux of efficiency optimal inductive power transfer systems

The design of contactless power supplies with inductive power transfer (IPT) is still a challenge even though such systems have become more and more established for various applications. This article presents an intuitive, educational introduction to IPT system design for practicing engineers who are new to the field. While following the path of the energy through the IPT system, the contactless power transfer is explained with a circuit-oriented approach, extended by an analysis of the field patterns and the energy flux across the air gap. Finite element method simulation results for the Poynting vector are shown to illustrate the power transfer process. Finally, a minimization of the reactive power demand of the IPT coils is performed, from which the general requirements for an efficiency optimal design of the IPT system can be intuitively understood.