Inductive Power Transfer Charging Research Articles

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 Family of IPT Battery Chargers With Small Clamp Coil for Configurable and Self-Sustained Battery Charging Profile

To self-sustain the constant current (CC) output to constant voltage (CV) output transition for inductive power transfer (IPT) chargers, the clamp coil assisted IPT battery chargers are better than the existing solutions due to the merits of no additional switching components, sensors, and control circuits. However, the clamp coil of these IPT chargers is bulky and hard to design, as the mutual inductances between the clamp coil and the main coupler coils are significant to the output performances. To facilitate the small clamp coil in the transmitter, this paper proposes a family of IPT battery chargers with a proper secondorder compensation network on the secondary side. The output thresholds of the IPT charger with the proper compensation can be readily configured to cope with the desired charging profile, and the clamp coil can be designed very small to decrease the corresponding cost and size. In addition, the proposed threecoil IPT charger still features automatic and smooth CC-to-CV transition to eliminate wireless communication, near unity power factor to minimize voltage-ampere (VA) ratings, soft switching to improve transfer efficiency, and open-circuit protection during CC charging. An experimental prototype of a 48 V/2.5 A battery charger is built to verify the analysis.

Design and Implementation of an IPT Charger with Minimum Number of Elements for Battery Charging Applications

Inductive power transfer (IPT) systems have been extensively studied and incorporated into various industrial applications. An IPT system with the capability to provide constant current output (CCO) and constant voltage output (CVO) is necessary to ensure optimal battery performance. However, the resistance of the battery will continue to increase during the charging process, making it difficult for the system to realize load-independent CCO and CVO with zero phase angle (ZPA) operation. Therefore, this paper proposes an LC/S compensated IPT system, which can provide CCO and CVO at fixed frequencies. ZPA operation can be maintained in both CC and CV modes for low reactive power loss. Moreover, the total number of compensation elements of the system is minimized, with only one compensation capacitor on the receiving side, which ensures not only the low cost of the system but also a compact receiver. Finally, the correctness and feasibility of the proposed system are verified with simulations and experiments.

A Load-Independent Current/Voltage IPT Charger with Secondary Side-Controlled Hybrid-Compensated Topology for Electric Vehicles

The inductive power transfer (IPT) method is an emerging charging technology that has some advantages over traditional plug-in systems. For example, it is safer, more convenient, and efficient, leading to its widespread acceptance. To design an IPT charger capable of providing a load-independent output, this paper proposes a secondary side-controlled hybrid-compensated topology used in the IPT system to charge the battery with a constant current/voltage output. According to an analysis of the Π-type network, effectively using the existing configuration compensation parameters and adding two AC switches to perform hybrid-topology switching reduces the system’s passive components. Additionally, the proposed IPT charger can easily realize zero-voltage switching. The secondary side-based control omits wireless communication links. Moreover, the control strategy is relatively simple, enhancing the system’s reliability. We designed a 1.4 kW experimental prototype with a 15 cm air gap between the transmitter and receiver to verify the proposed hybrid-compensated IPT system’s feasibility.

Overall Loss Compensation and Optimization Control in Single-Stage Inductive Power Transfer Converter Delivering Constant Power

A typical battery charging process consists of a constant-current (CC) charging phase which is followed and completed by a constant-voltage charging phase. Moreover, replacing the CC charging by constant-power (CP) charging can eliminate thermal problems and enhance the cycle life of the battery. This work aims to maximize the system efficiency of a single-stage inductive power transfer (IPT) charger by minimizing the overall losses using a CP charging scheme. The single-stage CP IPT charger employs series-series compensation and adopts an active rectifier on the secondary side. Based on a time-domain model, the conditions of zero voltage switching (ZVS) and minimum circulating reactive power are derived. Then, the power losses in the magnetic coupler, inverter and active rectifier are analyzed and optimized under CP output condition. Combining the conditions of ZVS, minimum circulating reactive power, and minimum overall losses, we propose a novel optimal control strategy to maintain CP output and maximum efficiency throughout the charging process. In addition, the proportional integral controller is not needed. Finally, a 120-W experimental prototype is built to verify the performance of the proposed control strategy. Experimental results demonstrate high precision CP output and an efficiency of around 87.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> for the proposed single-stage inductive power transfer battery charger.

Design and Realization of an Inductive Power Transfer for Shuttles in Automated Warehouses

The inductive power transfer (IPT) is expected to greatly contribute towards electrification in transportation. In fact, IPT charging technology has the potential to overcome several limitations of conductive charging: in particular, the process can be fully automatable, and both static and dynamic charging are allowed, thus reducing the size of the battery pack. Additionally, safety is increased due to the absence of safety issues related to loss of cable insulation or to the unwanted interruption of the plug-socket connection. This paper presents, from a systematic approach, the design and realization of a prototype for IPT charging of autonomous shuttles in automated warehouses. First of all, the typical mission profile of the shuttle was properly identified, and a storage system based on power-oriented electrochemical cells was sized. Based on that, the architecture of the IPT system was chosen, both for transmitting and receiving sections. The pads were designed for this purpose, by considering the geometric constraints imposed by the manufacturer, through the utilization of the finite elements method. Finally, the power electronic circuitry was also designed. Numerical simulations of the components, as well as of the complete system, were performed and a prototype was built to widely verify the correspondence of the simulation outputs with the results obtained from an experimental measurements campaign.

A Novel Clamp Coil Assisted IPT Battery Charger With Inherent CC-to-CV Transition Capability

A constant current (CC) output followed by a constant voltage (CV) threshold is usually needed for an inductive power transfer (IPT) charger to comply with the battery charging profile. This letter proposes a novel clamp coil assisted IPT battery charger that features inherent, passive, automatic, and smooth CC-to-CV transition. Since the CC-to-CV transition eliminates the necessity of state-of-charge detection, wireless feedback communication, and active control, the proposed IPT charger is rugged and reliable. The inherent CC-to-CV transition capability also tackles the open-circuit risk during a CC charging process. As minimalist design is achieved in the secondary, the proposed IPT charger is suitable for wireless onboard charging applications. Near-unity power factor design is also considered to minimize the voltage-ampere rating and permits soft switching. Experiment results validate the inherent CC-to-CV transition capability.

A brief review: basic coil designs for inductive power transfer

The inductive power transfer (IPT) has contributed to the fast growth of the electric vehicle (EV) market. The technology to recharge the EV battery has attracted the attention of many researchers and car manufacturers in developing green transportation. In IPT charging system, the coil design is indispensable in enhancing the EV battery charging process performance. This paper starts by describing the two charging techniques; static charging and dynamic charging before further presents the IPT system descriptions. Afterwards, this paper describes a brief review of coil designs which discusses the critical factors that affect the power transmission efficiency (PTE) including their basic designs, design concepts and features merits. The discussions on the basic coil designs for IPT are of the circular spiral coil (CSC), square coil (SC), rectangular coil (RC), and double-D coil (DDC). Furthermore, the significant advantages and limitations of each research on different geometries are analyzed and discussed in this paper. Finally, this paper evaluates some essential aspects that influence the coil geometry designs in practical.

Control Scheme of a Bidirectional Inductive Power Transfer System for Electric Vehicles Integrated into the Grid

Inductive power transfer (IPT) systems have become a very effective technology when charging the batteries of electric vehicles (EVs), with numerous research works devoted to this field in recent years. In the battery charging process, the EV consumes energy from the grid, and this concept is called Grid-to-Vehicle (G2V). Nevertheless, the EV can also be used to inject part of the energy stored in the battery into the grid, according to the so-called Vehicle-to-Grid (V2G) scheme. This bidirectional feature can be applied to a better development of distributed generation systems, thus improving the integration of EVs into the grid (including IPT-powered EVs). Over the past few years, some works have begun to pay attention to bidirectional IPT systems applied to EVs, focusing on aspects such as the compensation topology, the design of the magnetic coupler or the power electronic configuration. Nevertheless, the design of the control system has not been extensively studied. This paper is focused on the design of a control system applied to a bidirectional IPT charger, which can operate in both the G2V and V2G modes. The procedure design of the control system is thoroughly explained and classical control techniques are applied to tailor the control scheme. One of the advantages of the proposed control scheme is the robustness when there is a mismatch between the coupling factor used in the model and the real value. Moreover, the control system can be used to limit the peak value of the primary side current when this value increases, thus protecting the IPT system. Simulation results obtained with PSCADTM/EMTDCTM show the good performance of the overall system when working in both G2V and V2G modes, while experimental results validate the control system behavior in the G2V mode.

Variable parameter and variable frequency‐based IPT charging system with configurable charge current and charge voltage

Variable parameter (VP) or variable frequency (VF) methods for load-independent output current or output voltage in inductive power transfer (IPT) systems have been widely studied. This study proposes an IPT system based on series-series compensation topology with VP and VF methods to achieve constant-current–constant-voltage (CC–CV) charging for electric bicycles (EBs). The proposed IPT system can operate in CC and CV modes regardless of load conditions at two different operating frequencies with corresponding values of compensation capacitors. The rating current/voltage of the proposed method is configurable by altering the compensation capacitor and operational frequency. Therefore, one charging stand can be shared by various EBs to save the space and to cut the overall cost. Only one capacitor is needed for one EB specification. The proposed IPT system can achieve zero-voltage switching under all load conditions. An experimental prototype with two ratings of 48 V/3A and 60 V/4A is built to verify the feasibility of the proposed method. The experimental results demonstrate the feasibility of the proposed method.

Development of a Cross-Type Magnetic Coupler for Unmanned Aerial Vehicle IPT Charging Systems

Inductive power transfer (IPT) is an optimal way for the unmanned aerial vehicle (UAV) wireless charging. The magnetic coupler is the key component in the IPT system, which determines the power transmission capacity and efficiency in IPT system. Due to the particularity of UAV application, the magnetic field height should be strictly limited to avoid the damage caused by high frequency magnetic field heat the UAV's metal equipment. A cross-type magnetic coupler with receiving coil placed on UAV's one landing gear was proposed to solve this problem, but it has the possibility of making UAV fuselage imbalance. Therefore, a novel cross-type magnetic coupler is proposed to overcome its difficulties in this paper, and most of magnetic fields are restrained to be lower than UAV's landing gear height h 1 = 145mm, which will not cause damage to the UAV's equipment. And a simple and practical iterative method for designing the magnetic coupler geometry parameters is proposed, with simplification of the complex design process for the finite element analysis, improves the design efficiency. The experimental results show that the system can charge the 260W UAV normally with the system efficiency of 91.577% within the misalignment range of X-axis direction 25mm, Y-axis direction 40mm and rotation 25.

Decoupling Circuit for Automated Guided Vehicles IPT Charging Systems With Dual Receivers

It is more efficient to employ inductive power transfer (IPT) systems to charge automated guided vehicles (AGVs) than traditional plug-in systems. In order to provide independent and different charging power for the driven system and the control system of AGVs simultaneously, this letter proposes a coaxial dual-receiver structure and a decoupling circuit, which utilizes a passive component connected with two receiving coils to cancel out the mutual inductance between each other. By using this decoupling method, the two receiving coils could be treated as independent receivers without precise placement or additional transformers. First, the decoupling model is analyzed in detail, and the value of the decoupling component is given without any restriction of the ratio of their current. Then, the structure of the dual receiver is designed. Finally, an IPT system with one transmitter and dual receivers is built to verify the feasibility of the proposed method. Experimental results show that when one of the loads varies from 20 to 80 Ω, the voltage fluctuation of the other load is as small as 1.36% with decoupling, whereas 54.46% of voltage fluctuation without decoupling. The results validate that the proposed method is suitable for the application requiring dual independent outputs in the same equipment.

Variable-Parameter T-Circuit-Based IPT System Charging Battery With Constant Current or Constant Voltage Output

Load-independent output characteristics of inductive power transfer (IPT) systems are increasingly popular in battery charging. This paper proposes a novel variable-parameter T-circuit (VT) for an IPT system charging a battery with constant current (CC) or constant voltage (CV) output. The VT can transfer a CC/CV input to a CC or CV output by using an ac switch and a passive component (inductor or capacitor). An IPT system with a VT for CC–CV charging can reduce the number of passive components and ac switches. Besides, the proposed VT merits more design freedom of charge current/voltage with the constraints imposed by the loosely coupled transformer parameters compared to that of the traditional one. In addition, there are three kinds of VTs for various IPT charging systems with different requirements. A 400 W laboratory-scale prototype with a 150 mm air gap was built to verify the theoretical analyses. Both electronic load and lead-acid battery are utilized to verify the charging profile of the proposed method. The experimental results of the IPT system indicate that the fluctuation of the charging current in CC mode is less than 2%, and the change rate of charging voltage in CV mode is within 2.9%. The maximum overall efficiency 93.93% of the charging system is achieved from a dc 110 V input to a dc 100 V output.

An IPT Battery Charger With Near Unity Power Factor and Load-Independent Constant Output Combating Design Constraints of Input Voltage and Transformer Parameters

Inductive power transfer (IPT) techniques are becoming popular in battery charging applications due to some unique advantages compared to the conventional plug-in systems. A high-performance IPT charger should provide the battery with an efficient charging profile consisting of constant charging current and constant charging voltage. However, with a wide load range, it is hard to realize the initial load-independent constant current (CC) and the subsequent load-independent constant voltage (CV) using a single IPT converter while maintaining nearly unity power factor and soft switching of power switches simultaneously. This paper systematically analyzed the characteristics of an LCC – LCC compensated IPT converter and proposed a design method to realize the required load-independent CC and CV outputs at two zero-phase angle frequencies. The design also combats the constraints of an IPT transformer and input voltage, thus facilitating the use of a simple duty cycle control operating at two fixed frequencies for both CC and CV operations. The design criteria, control logic, and sensitivities of compensation parameters to the input impedance and load-independent output are discussed. Finally, an IPT battery charger prototype with 1 A charging current and 24 V battery voltage is built to verify the analysis.

Multiple Output Inductive Charger for Electric Vehicles

Multiple output chargers have widely been adopted in various electronic devices due to their benefit concerning cost, power density, and space for installation. On the contrary, inductive power transfer (IPT) has been applied increasingly in electric vehicles (EVs) since it is safer and more convenient as compared to conductive chargers. However, research works on multiple output chargers using an IPT system for EV charging applications are rarely presented. This paper proposes a new concept of a multiple output IPT charger, which can charge several output batteries independently and simultaneously by adopting only one full bridge inverter at the primary side combining with multiple transmitters. A total of two possible IPT-coil structures are analyzed, and the minimum distance between each channel's coils is determined to neglect the cross-coupling between them. A total of two options are proposed to attain a zero phase angle (ZPA) condition for the primary inverter of the proposed system. First option is to operate the compensation tanks of every output channel at exact ZPA frequencies. The other option is to let one channel work in the inductive region of its input impedance and other channel work in the capacitive region. By adopting an appropriate design, the reactive powers of these tanks can be nearly canceled by each other and the phase of inverter current can be nearly in-phase with the input voltage as a result. A total of two proposed options are compared to give recommendation whether option 1 or 2 should be selected according to various applications’ requirements. To simplify control complexity, IPT output current sources topologies are selected, compared, and analyzed to construct the proposed multiple output system in both above-mentioned options. Double-sided LCC and series–parallel topologies are adopted to demonstrate the proposed idea for options 1 and 2, respectively. In order to verify feasibility and validity of the proposed method, experimental results of two output channels with the total output power of 1.5 kW are provided. Experimental results indicate that the ZPA is achieved for the primary inverter with both of the above-mentioned options even under different load conditions. Some comparisons between the conventional and the proposed IPT charging structure in terms of cost, reliability, and complexity are included in the discussion section.

Cost‐effective inductive power transfer charging system for electric bicycles with variable charging current using primary‐side detuned series‐series topology

Due to the convenience and long travelling distance, electric bicycles (EBs) are becoming more and more popular. Charging EBs with inductive power transfer (IPT) technology can free people from wearisome plugging actions and avoid electric shock hazards. However, the cost, including component cost and control cost, is a big challenge for the extensive promotion of the IPT charging systems (IPTCSs) for EBs. This article proposes an IPTCS using primary-side detuned series-series (SS) compensation topology, cancelling control scheme and reducing the component cost. With the proposed parametric design method, the IPTCS can operate with variable charging current according to the variable equivalent resistance of a battery. Besides, the inductive input impedance is guaranteed to achieve soft switching for the high-frequency inverter. An experimental setup is constructed to validate the proposed method. The performance shows that the charging current decreases from 1.8 to 0.1 A, and charging voltage increase from 42.23 to 54.01 V during the whole charging process, where the maximum efficiency of the IPTCS can reach up to 92.8%. The results demonstrate the proposed IPTCS is a cost-effective and potential solution for charging EBs.

A Misalignment-Tolerant Series-Hybrid Wireless EV Charging System With Integrated Magnetics

Electric vehicles (EVs) are becoming increasingly popular as a mean of mitigating issues associated with fossil fuel consumption in transportation systems. A wireless inductive power transfer (IPT) interface between EV and the utility grid has several key advantages, such as safety, convenience, and isolation. However, physical misalignments between the pads of IPT charging systems used in EVs are unavoidable and cause variations in key system parameters, significantly increasing losses and affecting power throughput. This paper presents a novel series-hybrid topology in which the series inductors of the primary and pick-up inductor–capacitor–inductor ( LCL ) networks are integrated into polarized magnetic couplers to improve the system performance under pad misalignment. A mathematical model is developed to investigate the behavior of the proposed system under misalignment. To demonstrate the viability of the proposed method, the results of a 3.3-kW prototype series-hybrid IPT system are presented, benchmarked against a conventional IPT system. Experimental results clearly indicate that the proposed system maintains the output power within ±5% of its rated power despite the pad misalignment. The proposed system is efficient, reliable, and cost effective in comparison to conventional LCL- and CL -compensated IPT systems.

Simulation Model of a 2-kW IPT Charger with Phase-Shift Control: Validation through the Tuning of the Coupling Factor

When applied to road vehicle electrification, inductive power transfer (IPT) technology has the potential to boost the transition from combustion engines to electric motors powered by a battery pack. This work focuses on the validation of a PSpice circuit model developed as a replica of a 2-kW IPT prototype with series-series compensation operating at 18.65 kHz. The laboratory prototype has the three stages commonly found in an IPT system: an inverter, controlled by the phase-shift technique, a coil coupling and a load. Simulations were run with the circuit model for three different distances between the two coils of the inductive coupling, all of which are of interest for practical chargers: 125, 150 and 175 mm. The validation approach was based on tuning the magnetic coupling factor for each distance and a set of ten load resistances, until the best match between the simulated and the experimental peak currents supplied by the inverter was found in each case. The coupling factors obtained from the simulation work are in good agreement with their experimental counterparts for the three distances, provided the duty cycle of the inverter output voltage is not too small. The circuit model developed is, therefore, able to reproduce the behavior of the laboratory prototype with sufficient accuracy over a wide range of distances between coils and loading conditions.

Comparison of Tripolar and Circular Pads for IPT Charging Systems

Recently, a magnetic pad called the tripolar pad (TPP) has been introduced for inductive power transfer (IPT) systems. This paper evaluates the effective coupling factor and leakage magnetic field of a 20-kW IPT system that uses a combination of TPP and circular pad (CP) topologies over a range of lateral displacements. The results show that the effective coupling factor and the leakage magnetic field of the TPP–TPP system are substantially better when the secondary is displaced away from ideal alignment. Leakage magnetic field is reduced up to 43% compared to the CP–CP system at the worst-case misalignment, which is due to the ability of the TPP–TPP system to generate and capture different types of magnetic field shapes. Simulation methods for both the TPP and CP are validated in the laboratory using a 2-kW system operating at 85 kHz.

Inductive Power Transfer for Massive Electric Bicycles Charging Based on Hybrid Topology Switching With a Single Inverter

It is more convenient and safer to employ inductive power transfer (IPT) systems to charge the battery pack of electric bicycles (EBs) than conventional plug-in systems. An IPT charging method suitable for charging massive EBs is proposed to achieve constant current (CC) and constant voltage (CV) output without feedback control strategies or communication link between transmitter side and receiver side. Two ac switches (ACSs) and an auxiliary capacitor utilized at receiver side are employed to be operated once to change the charging modes from CC mode to CV mode. The characteristics of the load-independent current output in the CC mode and load-independent voltage output in the CV mode are achieved by properly selecting the passive parameters of inductances and capacitors, so that no sophisticated control strategies are required to regulate the output as per the charging profile. The feasibility of proposed method has been verified with an experimental prototype in form of efficiency, stability of output current and voltage in CC/CV mode. The simple and economical approach is suitable for the massive EBs charging system with only one inverter, especially in China.