Wireless capacitive energy transfer system – preliminary results

PurposeThis paper aims to develop mathematical models of variously compensated wireless energy transfer (WET) systems. Attention is primarily paid to the derivation of the most important energy transfer characteristics such as efficiency and amount of transferred power. This paper discusses the main advantages and disadvantages of various compensation techniques to show their possible application areas. On the basis of these results, a designer will be able to quickly identify which compensation type suites as the best solution to fulfill a given system’s requirements.Design/methodology/approachFirst, the current state in the field of mathematical modeling of WET systems is introduced. Next, the non-resonant magnetic-coupled circuit together with four most common resonant magnetic-coupled circuits is analyzed. The equivalent circuit models using loop currents methodology is applied to the analyses. The proposed methodology is experimentally verified by the laboratory measurement of selected circuit topology. The main contribution of the proposed methodology lies in its quick applicability on more complicated or extended systems while keeping a relatively good match with the real system’s behavior.FindingsThe authors have presented the usage of a simple and accurate methodology for investigating variously compensated WET systems. Electrical engineers who require effective and powerful tools for the identification of basic WET systems properties will find this methodology to be of extensive help.Research limitations/implicationsThe analyses consider only the sinusoidal type of supply voltage; so, it is valid mainly for the close range of the resonant state. Nonlinearities cannot be taken into account.Practical implicationsThis research may be applied in the field of WET systems.Originality/valueResearch in the area of power electronic systems, which provides a clear and straightforward procedure for WET system identification, will be helpful to most practical technicians who are not well versed in areas of physical-based phenomena.

The current trend puts emphasis on the efficiency of the all electronics devices. For this reason, it is necessary to maximize the efficiency of the wireless energy transfer system as well as on other electronic devices. Therefore, this article deals with the most suitable working point analysis of the serial–serial WET system. The core of the article contains the simulation analysis at the various loads and various coupling coefficients. Experimental measurements were made on the existing prototype and the results were compared with the results from the simulation analysis. The main outcome of this paper is thus detailed investigation of operational point of WET system in order to meet the highest possible system efficiency together with the highest possible level of transferred power.

Wireless energy transfer (WET) is potentially a promising solution to provide convenient and reliable energy supplies for energy-constrained networks, and has drawn growing interests recently. To overcome the significant propagation loss over distance, employing multi-antennas at the energy transmitter (ET) to more efficiently direct wireless energy to desired energy receivers (ERs), termed energy beamforming, is an essential technique for WET. However, the achievable gain of energy beamforming crucially depends on the available channel state information (CSI) at the ET, which needs to be acquired practically. In this paper, we study the optimal design of one efficient channel-acquisition method for a point-to-point multiple-input multiple-output (MIMO) WET system, by exploiting the channel reciprocity based on which the ET estimates the CSI via dedicated reverse-link training from the ER. Considering the limited energy availability at the ER, the training strategy should be carefully designed so that the channel can be estimated with sufficient accuracy, and yet without consuming excessive energy at the ER. To this end, we propose to maximize the net energy at the ER, which is the total energy harvested offset by that used for channel training. The optimal training design, including the number of receive antennas to be trained, as well as the training time and power allocated, is derived. Our result shows that training helps only when the following conditions are satisfied: (i) the channel coherence time is sufficiently large; (ii) the number of antennas at the ET is large enough; and (iii) the effective signal-to-noise ratio (ESNR) is sufficiently high; otherwise, no training should be applied and isotropic energy transmission is optimal.

This letter considers spectrum sharing between a multiuser multiple-input multiple-output (MIMO) wireless energy transfer (WET) system and a coexisting point-to-point MIMO wireless information transmission (WIT) system, where WET generates interference to WIT and degrades its throughput performance. We show that due to the interference, the WIT system suffers from a loss of the degrees of freedom (DoF) proportional to the number of energy beams sent by the energy transmitter (ET), which, in general, needs to be larger than one to optimize the multiuser WET with user fairness consideration. To minimize the DoF loss in WIT, we further propose a new single-beam energy transmission scheme based on the principle of time sharing, where the ET transmits one of the optimal energy beams at each time. This new scheme achieves the same optimal performance for the WET system, and minimizes the impact of its interference to the WIT system.

The effect of various parameters on the resonance-based wireless energy transfer system has been investigated to obtain the design steps for efficient wireless energy transfer. Both theoretically and experimentally, it has been observed that every system has its own strongly coupled region that is an optimum frequency band for which maximum energy transfer occurs. The frequency band of the strongly coupled region changes with the coil size, structure, physical spacing, relative location, and material properties of the wire. Based on the theoretical results, experiments have been carried out to demonstrate the effectiveness and characteristics of the resonant wireless energy transfer method. It is found that the energy transfer efficiency reaches maximum at resonant frequency. The energy transfer efficiency is further enhanced by changing the configuration of coil and through low-resistance wire with high-quality factor. The analyses will give future guidelines for designing a compact efficient wireless energy transfer system to energize macro as well as micro devices used for various applications.

This paper presents a miniature wireless energy transfer system design for implantable pressure sensor used for health monitoring applications. The implantable pressure sensor can be wirelessly powered through strongly coupled magnetic resonance based wireless energy transfer system. The wireless power transfer system has been built up by using a power transmitting circuit which will be placed outside the body and a receiving unit connected to the implantable pressure sensor to be kept inside the body. Experimentally, it has been found that the wireless power transfer from the transmitting coil to the implantable receiving coil depends on the operating frequency, separation distance between the coils and configuration of the coils. It has been found that maximum wireless power transfer occurs from the transmitting unit to the implantable receiving unit at the operating resonant frequency of the system. At the resonant frequency of 562 kHz and optimum load of 40 Ω, a maximum power of 0.186 W and energy transfer efficiency of 26% have been achieved wirelessly with a separation distance of 3 cm between the transmitter and receiver resonators. Electromagnetic simulation has also been carried out using the different forms of transmitting and receiving coils in order to obtain a strong magnetic coupled wireless energy transfer system, which plays an important role in the energy transfer efficiency.

A compact wireless energy transfer scheme for delivering power to the implantable electronic devices has been presented here. The wireless energy transfer system is built by using a printed spiral receiving resonator with a cylindrical source resonator to transfer energy wirelessly through strongly coupled magnetic resonance. Experimentally, it is found that the wireless power transfer efficiency reaches the maximum at the resonant frequency, and the efficiency decreases with the increase of the distance between the source and receiver coils. The proposed design has the significant advantage of being easier to implement for biomedical applications due to sizeable reduction in volume required on the implantable devices.

This chapter provides an overview of the main energy harvesting (EH) technologies and their relevant role in present and future internet of things (IoT) deployments. EH technologies for wireless machine-type devices can be mainly classified into the following two categories: ambient EH, and dedicated EH. The chapter emphasizes on RF–EH, and highlights its advantages compared to competing EH technologies reduced form-factor implementation and native multi-user support. RF–wireless energy transfer (WET) systems consist of three key components: RF transmitters, medium, and EH node. It focuses on the non-decreasing EH transfer function with the incident RF waveform power as sole input. The chapter describes the general architecture of an RF–EH IoT network, and the main layouts for wireless information transfer (WIT) and WET along with potential applications. WET, as a pivotal component of RF–EH networks, is fundamental for realizing the Internet of Energy paradigm.

This paper presents a wireless transcutaneous energy transmission system utilizing the magnetic coupling of coils. No physical wire connection is required between the circuits inside and outside the body. Because the transformer is the contactless transformer, the coupling efficient of the transformer is not good as normal transformer. The parameter of the leakage inductance of transformer will be larger than the magnetizing inductance of transformer. An LLC resonant converter is used outside the body. The LLC resonant converter could have higher power conversion efficiency to improve wireless transcutaneous energy transmission system efficiency. In addition, the soft-switching structure of a LLC resonant converter is utilized. A phase locked loop is adopted to control the LCC resonance to facilitate the steady electrical energy transfer. According to the experimental results, the system can deliver an output power around 1W to the load circuits inside the body and the output voltage can be regulated at 4V.

This chapter examines simultaneous wireless information and power transfer (SWIPT) scenarios. It discusses the main SWIPT receivers, namely, separate and co-located receivers. The chapter provides numerical examples on the performance of the designed SWIPT precoding strategy. It focuses on a co-located SWIPT system, where a HAP serves a set S of devices performing both energy harvesting and information decoding in a given frequency band. The chapter illustrates some numerical results on the performance of the time switching and power splitting protocols. It also discusses some specific promising approaches to boost the performance of SWIPT systems for general wireless energy transfer (WET)-powered internet of things networks. WET and SWIPT systems are subject to non-linear responses that are often model-intractable unless too strong assumptions are adopted. The chapter concludes with an overview of some potential techniques to enable efficient SWIPT in future networks.

A general equivalent circuit model is developed for a wireless energy transfer system composed of multiple coils via coupled magnetic resonances. To verify the developed model, four types of wireless energy transfer systems are fabricated, measured, and compared with simulation results. To model a system composed of n-coils, node equations are built in the form of an n-by-n matrix, and the equivalent circuit model is established using an electric design automation tool. Using the model, we can simulate systems with multiple coils, power sources, and loads. Moreover, coupling constants are extracted as a function of the distance between two coils, and we can predict the characteristics of a system having coils at an arbitrary location. We fabricate four types of systems with relay coils, two operating frequencies, two power sources, and the function of characteristic impedance conversion. We measure the characteristics of all systems and compare them with the simulation results. The flexibility of the developed model enables us to design and optimize a complicated system consisting of many coils.

Accomplishing equilibrium in terms of transfer efficiency for dual-band wireless energy transfer (WET) system remains as one of key concerns particularly in the implementation of a single transmitter device which supports simultaneous energy and data transfer functionality. Three stages of design method are discussed in addressing the aforementioned concern. A single layer dual-band printed spiral resonator for non-radiative wireless energy transfer operating at 6.78 MHz and 13.56 MHz is presented. By employing multi-coil approach, measured power transfer efficiency for a symmetrical link separated at axial distance of 30 mm are 72.34% and 74.02% at the respective frequency bands. When operating distance is varied between 30 mm to 38 mm, consistency of simulated peak transfer efficiency above 50% is achievable.

This paper proposes a novel channel estimation method and a cluster-based opportunistic scheduling policy, for a wireless energy transfer (WET) system consisting of multiple low-complex energy receivers (ERs) with limited processing capabilities. Firstly, in the training stage, the energy transmitter (ET) obtains a set of Received Signal Strength Indicator (RSSI) feedback values from all ERs, and these values are used to estimate the channels between the ET and all ERs. Next, based on the channel estimates, the ERs are grouped into clusters, and the cluster that has its members closest to its centroid in phase is selected for dedicated WET. The beamformer that maximizes the minimum harvested energy among all ERs in the selected cluster is found by solving a convex optimization problem. All ERs have the same chance of being selected regardless of their distances from the ET, and hence, this scheduling policy can be considered to be opportunistic as well as fair. It is shown that the proposed method achieves significant performance gains over benchmark schemes.

Energy beamforming (EB) is a key technique for achieving efficient radio-frequency (RF) transmission enabled wireless energy transfer (WET). By optimally designing the waveforms from multiple energy transmitters (ETs) over the wireless channels, they are constructively combined at the energy receiver (ER) to achieve an EB gain that scales with the number of ETs. However, the optimal design of transmit waveforms requires accurate channel state information (CSI) at the ETs, which is challenging to obtain in practical WET systems. In this paper, we propose a new channel training scheme to achieve optimal EB gain in a distributed WET system, where multiple separated ETs adjust their transmit phases to collaboratively send power to a single ER in an iterative manner, based on one-bit feedback from the ER per training interval which indicates the increase/decrease of the received power level from one particular ET over two preassigned transmit phases. The proposed EB algorithm can be efficiently implemented in practical WET systems even with a large number of distributed ETs, and is analytically shown to converge quickly to the optimal EB design as the number of feedback intervals per ET increases. Numerical results are provided to evaluate the performance of the proposed algorithm as compared to other distributed EB designs.

This work presents the study of two transformers with high tolerance to misalignments for application in battery charging of Autonomous Vehicles (AUV). These transformers are composed of two topologies normally used in wireless energy transfer systems: Solenoid-Solenoid and Solenoid-Planar Spiral. To develop the study, a single-phase Inductive Power Transfer (IPT) system was simulated in the PSIM software. A voltage source inverter is the power supply of the transformer and a full wave rectifier with a capacitor filter is the load. The IPT system was simulated with the series-series compensation and the transformers were simulated at FEMM software. The results show that the transformer coupling factor ranges from less than 10 %, in both cases, even with a 50 % coaxial misalignment between primary and secondary.