Analytical Optimization of a Litz Wire Spiral Coil Based Underwater IPT System

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.

This article studies magnetic forces between transmitter (Tx) and receiver (Rx) coils in an inductive power transfer (IPT) system aiming to use those forces to align the coils and, consequently, improve power transfer. Due to its popularity, the analysis is conducted on a series–series compensated IPT system with planar spiral coils. The proposed method utilizes the bifurcation operation mode of the system and unloaded resonating receiver to maximize attractive force between magnetic couplers. Three-dimensional finite-element method simulations indicate that high-power IPT systems can develop enough attractive force to align coils even under nominal current. Regardless of the coil shape, e.g., spiral or Double-D (DD), the attractive forces tend to align the coils. Hence, a smart charging station can be devised based on self-aligning capability. Furthermore, this article proposes a mechanical structure to facilitate the attractive lateral force for the alignment of high power applications, i.e., wireless fast-charging stations. The forces are analyzed, modeled, and simulated for a 100-kW IPT system with an operating frequency of 20 kHz, while the self-aligning capability is experimentally verified on a downscale 11-kW prototype.

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 relatively large air gap, the magnetic coupling coefficient of the IPT system is significantly lower than that with tightly coupled transformer. As a result, the efficiency of the IPT system is always a main concern for applications with possible gap variation or misalignment condition. To ensure high power transfer efficiency, these IPT systems should have high tolerance for different gap variation and horizontal misalignment conditions. In this paper, the effect of coupling coefficient deviation to compensation network efficiency is analyzed, and design considerations to reduce gap and misalignment effects for the IPT system are proposed. By using finite-element analysis simulation method, the performance of different transmitter and receiver coil dimensions is compared. In order to validate the performance of the proposed design considerations, a 100-W hardware prototype with two sets of LCT is built and the corresponding experiments are carried out. As compared to the symmetrical LCT architecture, the proposed asymmetrical LCT prototype improves the coupling coefficient reduction from 68% to 28% when the gap varies from 6 to 20 mm and from 89% to 31% when the misalignment ranges from 0 to 50 mm. Therefore, the efficiency deviation for the asymmetrical LCT is maintained within 3.5% over the entire tested gap variation and misalignment ranges.

A dynamic inductive power transfer (IPT) system is a safe and convenient solution to address the issues related to the limited battery capacity and travel distance of electric vehicles (EVs). In recent years, practical aspects of dynamic IPT systems have been investigated to advance various IPT technologies from laboratories to roadways. This paper suggests a configuration to mitigate some of the installation and maintenance concerns of IPT roadways by proposing a switchable inductively coupled connector. Besides providing galvanic isolation, the inductively coupled connector helps maintain a constant and load-independent current in the primary coupler. Moreover, each primary coupler is connected to a common H-bridge through a single DC switch minimizing the number of components required to energize each coupler independently. A mathematical analysis and simulation results have been provided to validate a scaled 3.3kW prototype IPT system employing the proposed configuration.

To improve misalignment tolerance for an inductive power transfer (IPT) system, a third-coil is employed to reversely connect with the primary coil of the loosely coupled transformer (LCT) in series. The LCT with a third-coil (LCT-TC) not only can improve the misalignment performance in x - and y -directions, but also does not affect the inherent output characteristics (such as constant current or voltage output) of original compensation topologies. In addition, the proposed approach can keep the IPT system operating with relatively high efficiency against misalignment. Then, a detailed design method of LCT-TC is presented. Finally, a double-side LCC-compensated IPT system is chosen as an example to verify the feasibility of proposed LCT-TC. A 3.4-kW prototype is constructed, and experimental results show that the proposed method has a good misalignment performance. The LCC-LCC IPT system with LCT-TC can retain 96% of the well-aligned power at 40% misalignment, and the end-to-end (dc–dc) overall system efficiency is at least 92%. Besides, the fluctuation of the output current is [–2%, 5%] while the load varies from 15 to 34 Ω within 40% misalignment.

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.

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.

The efficiency of an inductive power transfer (IPT) system is greatly affected by lateral misalignment between the transmitter and receiver coils. This study proposes a hexagonal arrangement of multi-coil configuration IPT system to improve misalignment tolerance while maintaining the transfer efficiency. Key parameters including equivalent self and mutual inductance of various coil connections are examined. The magnetic characteristics including flux distribution and density, and mutual inductance are simulated using COMSOL Multiphysics software package. Experimental results of the proposed multi-coil IPT system are given and compared with the conventional two-coil IPT system. Simulation and experimental results have shown that the proposed multi-transmitter coil configuration can increase misalignment tolerance compared with conventional system.

This paper proposes a self-tuning controller for a multi-level inductive Electric Vehicle (EV) battery charger application. By controlling the energy injection frequency of the Inductive Power Transfer (IPT) system, multiple charging levels (4 in number) are achieved. Maximum performance is leveraged by the proposed IPT system using its capability of self-tuning the switching operations to the natural resonant frequency of the IPT system, thereby benefiting from soft-switching operations (zero-current switching).Either a digital or analog control circuit can be used to implement the proposed controller. The results are shown by simulating the proposed controller with different charging levels using MATLAB/Simulink. These results show that the proposed controller effectively enables IPT-based contactless EV charging at multiple charging levels, with soft-switching operations. This self-tuning capability is specifically useful in IPT systems that have variable resonance frequency.

The single resonant inverter is widely employed in typical inductive power transfer (IPT) systems to generate a high-frequency current in the primary side. However, the power capacity of a single resonant inverter is limited by the constraints of power electronic devices and the relevant cost. Consequently, IPT systems fail to meet high-power application requirements, such as those in rail applications. Total harmonic distortion (THD) may also violate the standard electromagnetic interference requirements with phase shift control under light load conditions. A power regulation approach with selective harmonic elimination is proposed on the basis of a parallel multi-inverter to upgrade the power levels of IPT systems and suppress THD under light load conditions by changing the output voltage pulse width and phase shift angle among parallel multi-inverters. The validity of the proposed control approach is verified by using a 1,412.3 W prototype system, which achieves a maximum transfer efficiency of 90.602%. Output power levels can be dramatically improved with the same semiconductor capacity, and distortion can be effectively suppressed under various load conditions.

In this paper, a new Modular differential-mode Class-D Power Amplifier (PA) is analyzed and designed for Inductive Power Transfer (IPT) systems that are compatible with the A4WP standard. Multiple receivers IPT systems need more power, especially with integrating more receivers, and an ultra-wide range of power processing. The modular structure of the proposed PA offers flexibility, higher reliability, and inherent power scalability. The transmitted power range can be optimized and scaled to any power level making the PA design effectively suitable for multiple receivers’ IPT systems. Also, independent control for Class-D PA is proposed to increase efficiency and enhance overall performance. The proposed control has a feature of disabling needless legs in low power range which happened at activating a low number of utilized receivers. GaN power transistors are used in the proposed modular PA to enhance the performance at high frequency and provide high efficiency while achieving zero voltage switching (ZVS) operation. Detailed mathematical analysis along with simulation results are provided to validate the performance features of the proposed modular PA.

This paper presents a method for finding the optimum load resistance that maximizes the power efficiency of a tuned-resonant inductive power transfer (IPT) system. In this method, the equivalent AC circuit of the IPT system is transformed to match the topology of a reference ladder prototype. This simplifies the design problem, because the ladder prototype offers intuitive and accurate closed-form approximations for the optimum load resistance and maximum power efficiency. The process is graphical in the sense that manipulations and transformations are made directly on the circuit diagram. Compared to traditional circuit analysis, the ladder prototype approach does not entail complicated systems of equations or matrix manipulations. We show the utility of our method by designing a practical IPT system.

This paper presents the hardware design of a novel and reliable data link for charging electric vehicles by an inductive power transfer (IPT) system. The simultaneous transmission uses the contactless near field of one common pair of coils. The data link can amongst others exchange the status information between the vehicle and the charging station. Due to its structure, most existing systems can be upgraded by this highly integrated data link without significant changes. One key component for the data link is the frequency separating filter (FSF). Its structure and design as part of the communication system as well as the interaction with the IPT system will be presented.

Efficiency maximization based on load optimization has been thoroughly investigated for the conventional single-input single-output (SISO) inductive power transfer (IPT) system. This paper further extends the problem for multiple-input multiple-output (MIMO) IPT system operating at a single frequency. For the MIMO IPT system, efficiency maximization requires a joint optimization of loads—at the receivers—and input currents—in the transmitters. The optimal complex values of input currents and loads are derived by applying the first-order necessary condition, followed by the second partial derivative test. The derived maximum efficiency expression enables performance evaluation for any coil configuration, under any coil arrangement and at any frequency. Effectiveness and feasibility of the derived formulas are evaluated by electromagnetic simulations. Our work generalizes a theory on efficiency maximization for SISO, single-input multiple-output, multiple-input single-output, and MIMO systems.