Bifurcation Analysis in Weakly-Coupled Inductive Power Transfer Systems

Mobility, continuity and safety are crucial in charging and discharging system of electric vehicles (EV) in smart grid applications. Bidirectional inductive wireless power transfer (BIWPT) system is ideal choice for these services. With accurate and efficient system models in hand, the circuit designers can predict and optimize the system performance. In this paper, an accurate, intuitive, and comprehensive steady-state theoretical model is proposed and implemented in MatLab environment. This model is generalized and can be used for any magnetic design of BIWPT system with the same compensation topology. The model is able to predict the system currents, voltages, power, power factor and equivalent impedance. The proposed model is used to evaluate two different designs for LCL compensation topology based on impedance frequency response analysis. Also, general considerations for the filters design parameters are stated and verified in this paper. A Simulink MatLab model for 1 kW BIWPT system is built to verify the proposed theoretical analysis.

Wireless Power Transfer (WPT) systems have demonstrated their efficiency over a broad frequency spectrum. However, the design and the optimization of multi-MHz frequency WPT systems remain complex due to parasitic components specifically. This paper outlines a methodology for designing and optimizing a compact 13.56 MHz resonant inductive coupling WPT systems based on a GaN Class E inverter. The proposed design approach combines analytical modeling and advanced numerical simulations taking into account parasitic elements. The effectiveness of this approach is experimentally confirmed through a prototype, which shows an efficiency of 78% for a transmitted power of 43 W to a 5.54 cm³ coupler. The advanced modeling results perfectly match with the experimental ones (mismatch of only 2% for the evaluation of efficiency). The WPT system developed thanks to this method shows a power density among the highest ones in the non-mating connectors’ state of the art.

In an inductive wireless power transfer system, unavoidable lateral misalignment between the transmitter and the receiver leads to reactive power, which reduces the powertransfer-efficiency and limits the maximum output power under given input voltage. A tunable capacitor provides access to achieve low reactive power and maintain high power-transfer-efficiency. In this paper, the effects of misalignment on power transfer performance is investigated. A conventional capacitor tuning method is analyzed, and its limitations are identified. An innovative low loss online capacitor tuning method is proposed to automatically achieve low reactive power and maintain high power-transfer-efficiency under misalignment. The proposed designs are evaluated via simulation.

With the development of inductive wireless power transfer technology (IPT), electromagnetic compatibility (EMC) of the IPT system has attracted much attention. In this paper, the equivalent AC impedance model of LCC/S topology is established, and the conclusion that the output characteristics and power transfer efficiency (PTE) are related to mutual inductance M is obtained. To solve the problem of excessively large magnetic flux leakage of loosely coupling transformer (LCT), magnetic coupler with vertical and horizontal shielding is designed based on the method of magnetic flux constraint, and its finite element analysis (FEA) 3D model is established. A prototype is built for experiments. The maximum transmission efficiency of the prototype is 90.33%, and the minimum transmission efficiency is 88.20%. The FEA simulation and experimental results verify the feasibility of the magnetic shielding structure design method. The results show that the novel proposed magnetic shielding structure increases the strength of magnetic field, effectively reduces the eddy current loss caused by magnetic field leakage, and increases the anti-misalignment ability of the system.

Contactless power transfer is expected to be applied to many applications since it is convenience and safety. Inductive power transfer (IPT) is a kind of contactless power transfer schemes uses two coils. These coils are inductively coupled and power is transferred from primary coil to secondary coil when high frequency (a few tens of kHz) AC power supplies to primary coil. In many applications using IPT, received AC power is converted to DC power and then the power is charged to battery. Thus, two functions which are rectification and regulating voltage or current are required on the receiver (secondary) side. In this study, one of two types (buck type and boost type) of DC-DC converter connected to diode rectifier were applied to IPT system, and characteristics of each type were compared by experiments. As a result of the experiments, it was found that both rectifiers have two functions which are rectification and regulating voltage or current. It was also found that boost type is better in terms of regulation capability and of efficiency of resonant circuit.

An inductive power transfer (IPT) system usually consists of four parts: an AC-DC power factor correction (PFC) converter, a high frequency DC-AC inverter, a compensation network comprising a loosely coupled transformer (LCT) and the resonant capacitors, and a rectification output circuit. Due to the relative large air gap, the magnetic coupling coefficient of the IPT system is poor, different from the closely-coupled IPT systems. As a result, the efficiency of the IPT system is always a main concern for different applications. To ensure high power transfer efficiency, these IPT systems should have high tolerance for different gap variation and horizontal misalignment conditions. In this paper, some design considerations to reduce gap and misalignment effects for the IPT system is proposed. By using finite element analysis (FEA) simulation method, the performance of different transmitter and receiver coil dimensions are compared. In order to validate the performance of the proposed design considerations, a hardware prototype is built and the corresponding experiments are carried out. The experimental results shows that the LCT prototype could maintain coupling coefficient between 0.237∼0.212 within 40 mm horizontal misalignment.

Autonomous underwater vehicles (AUVs) are increasingly used for undersea exploration. The endurance of AUVs is limited by the onboard energy storage among which the battery systems dominate. Various underwater recharging methods are employed to increase the AUV range and autonomy. Currently, contact-based underwater recharging utilizes the wet-mate connector technology that requires a high-precision AUV docking, and is prone to electrical safety issues. To overcome these limitations, underwater wireless recharging techniques for AUVs have been explored in recent years. Wireless charging offers a safe and reliable method for autonomous power transfer between a charging station and a vehicle. This article reviews the state-of-the-art inductive wireless power transfer (IWPT) solutions for underwater applications and discusses the engineering challenges of the IWPT system design. Underwater environmental factors, such as seawater conductivity, temperature, pressure, water currents, and biofouling phenomenon, impose constraints on IWPT systems. A comprehensive review of AUV energy storage systems, docking methods, IWPT system control methods, and compensation networks is presented in this article. Based on the main operational and constructional principles, the AUV IWPT systems are categorized as loosely coupled transformers and resonant IWPT systems. Each of the categories is illustrated through their main design principles and implementations reported in the literature so far. Technical challenges, such as integration of IWPT system into an AUV hull, interoperability, alignment and retention issues, docking station sinking and stability, the design of pressure-tolerant charging electronics, data transfer, and the battery operation in the underwater environment are discussed in this article too. The article is concluded with the best practice overview of designing an IWPT system for AUVs.

The output characteristics and the transfer efficiencies of inductive power transfer (IPT) systems are affected by (but not limited to) the variation of parameters such as, variable load, misalignment between the primary and secondary coils, and resonance frequency detuning. This paper first analyzes the resonant conditions of all voltage-fed compensation topologies in IPT systems to achieve the load-independent voltage transfer characteristic at load-independent zero phase angle frequency. With these conditions, the parameters sensitivity to the key performance factors of the S-SP, LCC-S, LCC-P, and double-sided LCC compensated IPT systems are systematically investigated when considering the losses in coils and compensation networks. Comparisons of the quantitative sensitivity analysis and experimental results for all IPT systems are made in terms of the voltage transfer ratio and efficiency. These analyses can provide guidance for the selection of superior compensation networks to minimize the additional converter effort and simplify the control algorithm of closed-loop IPT systems.

For bidirectional inductive wireless power transfer systems, zero voltage switching (ZVS) of switching devices and system efficiency are always the keys to research. In this paper, the efficiency of the bidirectional dual-LCC compensation topology is firstly modelled, and the optimal bilateral modulation strategy is quantitatively derived. Then, a half-bridge modulation method under light load conditions is proposed. Compared with the full-bridge modulation strategy, the operating efficiency of the system is further improved. Finally, a 3.3 kW two-way wireless power transfer system simulation model is built in MATLAB. Compared with the full-bridge triple-phase-shift modulation strategy, it is proved that the half-bridge modulation scheme proposed in this paper has higher energy transfer efficiency under light load conditions.

The IPT system has been studied for underwater applications such as autonomous underwater vehicles (AUVs) and subsea sensors. However, it rarely comparatively shows the performance of the IPT system in air, freshwater, and seawater. Based on the fore‐mentioned research background, this paper presents a survey of the properties of the IPT system in different mediums. Here, a 100 W power‐level experimental IPT prototype is built and tested. The resonant frequency is set at 300 kHz with a gap range from 10 to 190 mm. The comparison is focused on the efficiency, mutual inductance, coupling coefficient, coil resistance, and quality factor of the IPT system. The IPT system is placed in air, freshwater, and seawater with the same settings. What's more, the magnetic fields of coupling coils in air, freshwater, and seawater are presented in this paper. This paper could be acted as a reference to optimize the IPT system and facilitate future IPT research for underwater applications by analysing the performance of the IPT system in different mediums. The 3D Ansys Maxwell simulation of the IPT system is also given here to study the magnetic fields.

Purpose This paper aims to present an approach to the design of the compensation networks (CNs) based on a genetic optimization algorithm. The algorithm is applied to CNs with T-topology and considers the effects of the parasitic series resistances of their inductive components. The effectiveness of the algorithm is verified using Bode diagrams and simulation results. Design/methodology/approach The paper at first describes the problem and the approach followed to reach a set of optimal solutions, then explains the optimization algorithm, reports the obtained solutions and selects the optimal CNs. Finally, the actual performance of the wireless power transfer system (WPTS) when the selected CNs are used are checked. Findings This approach gave interesting results and made available a number of different sizing solutions of complex networks in a very short time. Most of the obtained solutions outperform the widely used series-series compensation. An accurate post processing of the obtained result is mandatory to discriminate the solutions that could be implemented from those that in a real system would originate uncontrolled high frequency current oscillation. Originality/value This paper offers a rather new approach to solve the problem of sizing the CNs of a dynamic WPTS. This approach makes available a large number of optimal solutions to the problem in a short time, without solving complex system of equations.

This paper suggests a high efficiency inductive wireless power transfer system can be achieved by improving beaming field. Theoretical analysis, simulation results and experimental results are presented in this report. The coupling coefficient is enhanced through the use of multi-coils on the primary, ensuring a long distance transfer over a wide operating frequency range. It is a significant technique to overcome the shortcomings of wired charging. A prototype is constructed and the optimum air gap between the primary side and the secondary side for the power transmission is 15mm with 60 kHz of switching frequency. The results obtained reveals that asymmetric 4-coil resonator has greater power transfer efficiency for a similar gap compared to symmetric 4-coil resonator as the source coil effective inductance is boosted two times by intermediate coils at the primary side.

In this study, a series compensated WPT system is presented for low power DC load applications. Series LC resonant circuits are applied for both transmitter and receiver sides of WPT system to reduce the impedance at a specified operation frequency, and thus, ensure low power losses. The operation frequency is chosen as 109 kHz for the series compensated WPT system. Then, the series resonant LC filter is designed according to the operation frequency and WPT rating values. In addition, the power electronics systems with their controller and operation principle are demonstrated in depth. To investigate the performance of the proposed system, a 100 W series compensated WPT model is designed and constructed in Matlab/Simulink enviroment. Different simulation results are provided to illustrate the performance of the proposed WPT model. The simulation results show the stable operation of the proposed system under the designed system parameters.

Although the demand for high-power inductive power transfer (IPT) systems is on the rise, implementation of such IPT systems using low-cost semiconductor devices has been a challenge. This study presents a new IPT topology that facilitates easy integration of multiple IPT modules, which are made of low cost and freely available semiconductor components, to cater for high-power applications. An intermediate circuit, comprising an inductor-capacitor-inductor resonant network, serves as a contactless interface through which the modules of primary and secondary (pick-up) systems can be either series or parallel integrated. Inductor coils of the intermediate circuit and both primary and pick-up systems are magnetically coupled to allow for contactless power transfer. The proposed topology is parallel compensated to minimise its var requirement, and both the direction and amount of power flow are controlled by phase and/or magnitude modulation of voltages generated by primary and pick-up side converters. Theoretical analysis, together with simulations and experimental evidence of integrating four prototype bi-directional IPT systems to cater for 1.8 kW demand, is presented to show that the proposed new IPT topology is suitable for high-power applications, and flexible for both bi-directional and uni-directional contactless power transfer.

SummaryRectifier load in inductive power transfer system has nonlinear characteristics. However, the traditional analysis method equates it to a pure resistor, which leads to a certain deviation between the theoretical analysis and the actual circuit. This will reduce the accuracy of the inductive power transfer (IPT) system model and affect the soft switching operation of the inverter. In this paper, the IPT system with S‐type topology on the secondary side is studied. Firstly, the resistance–inductance characteristics of the rectifier load are analyzed by simulation, and then a second‐order circuit response model is established to solve the time‐domain expression of voltage and current. Then, the fundamental component of voltage and current is extracted by Fourier transform to calculate the impedance value of the rectifier load, and the mathematical calculation model of the rectifier load is established. On this basis, the influence of the inductive component of the rectifier load on the input impedance of the IPT system is analyzed. Then, a parameter design method for zero voltage switching is proposed for S‐S and LCC‐S topologies. Finally, an experimental platform of S‐S and LCC‐S IPT system is built. The correctness and effectiveness of the theoretical analysis and the proposed parameter design method are verified by experiments.