The development of capacitive power transfer (CPT) as a competitive wireless/contactless power transfer solution over short distances is proving viable in both consumer and industrial electronic products/systems. The CPT is usually applied in low-power applications, due to small coupling capacitance. Recent research has increased the coupling capacitance from the pF to the nF scale, enabling extension of CPT to kilowatt power level applications. This paper addresses the need of efficient power electronics suitable for CPT at higher power levels, while remaining cost effective. Therefore, to reduce the cost and losses single-switch–single-diode topologies are investigated. Four single active switch CPT topologies based on the canonical Cuk, SEPIC, Zeta, and Buck-boost converters are proposed and investigated. Performance tradeoffs within the context of a CPT system are presented and corroborated with experimental results. A prototype single active switch converter demonstrates 1-kW power transfer at a frequency of 200 kHz with >90% efficiency.

Single Active Switch Power Electronics for Kilowatt Scale Capacitive Power Transfer

Improved magnetic mirror models (IM3) for mono and dual coils with a finite width and infinite permeability are proposed in this paper. By introducing a mirror current, which is located at the same distance from a source current but with a smaller magnitude than the source current, the magnetic flux density of the mono and dual coils can be determined in a closed form. The ratio of the mirror current and source current is identified as a function of the width of the core plate and the distance between the source current and core plate, as rigorously derived from finite-element method simulations. Applying the proposed IM3 to the mono and dual coils used for wireless electric vehicles, the magnetic flux density over an open core plate is analyzed and its maximum points on the plate are found, which is crucial in the design of the coils to avoid local magnetic saturation. Furthermore, the magnetic flux density when a pick-up core plate is positioned over a primary core plate is also analyzed by introducing successive mirror currents. The proposed magnetic mirror models were extensively verified by experiments as well as site tests, showing quite promising practical usefulness.

Finite-Width Magnetic Mirror Models of Mono and Dual Coils for Wireless Electric Vehicles

One of the main concerns in traditional wireless sensor networks (WSNs) is energy efficiency. In this work, we analyze two techniques that can extend network lifetime. The first is ambient energy harvesting (EH), i.e. , the capability of the devices to gather energy from the environment, whereas the second is wireless energy transfer (ET), that can be used to exchange energy among devices. We study the combination of these techniques, showing that they can be used jointly to improve the system performance. We consider a transmitter–receiver pair, showing how the ET improvement depends upon the statistics of the energy arrivals and the energy consumption of the devices. With the aim of maximizing a reward function, e.g. , the average transmission rate, we find performance upper bounds with and without ET, define both online and offline optimization problems, and present results based on realistic energy arrivals in indoor and outdoor environments. We show that ET can significantly improve the system performance even when a sizable fraction of the transmitted energy is wasted and that, in some scenarios, the online approach can obtain close to optimal performance.

Joint Transmission and Energy Transfer Policies for Energy Harvesting Devices With Finite Batteries

charging is a method of moving power wirelessly. A power generating source system is placed near a power storing or power transferring system. An electromagnetic field is generated between the two objects and power is moved from one system to the other. Inductive charging is a way of moving power from a main system to a subsystem such as moving the power from the power grid to a local transformer. It is applied to a wide variety of systems from small hand-held devices to robotic platforms and electric vehicles. In this study, the working principle, advantages, disadvantages and limitations of inductive charging mats/pads used for electronic devices are discussed. The new advancements in inductive charging for transportation are also reviewed in this study.

State of the Art in Inductive Charging for Electronic Appliances and its Future in Transportation

One of the main concerns in traditional Wireless Sensor Networks (WSNs) is energy efficiency. In this work, we analyze two techniques that can extend network lifetime. The first is Ambient \emph{Energy Harvesting} (EH), i.e., the capability of the devices to gather energy from the environment, whereas the second is Wireless \emph{Energy Transfer} (ET), that can be used to exchange energy among devices. We study the combination of these techniques, showing that they can be used jointly to improve the system performance. We consider a transmitter-receiver pair, showing how the ET improvement depends upon the statistics of the energy arrivals and the energy consumption of the devices. With the aim of maximizing a reward function, e.g., the average transmission rate, we find performance upper bounds with and without ET, define both online and offline optimization problems, and present results based on realistic energy arrivals in indoor and outdoor environments. We show that ET can significantly improve the system performance even when a sizable fraction of the transmitted energy is wasted and that, in some scenarios, the online approach can obtain close to optimal performance.

Joint Transmission and Energy Transfer Policies for Energy Harvesting Devices with Finite Batteries

Strong coupled magnetic resonance has been convinced to be a new and efficient wireless power transfer way by the previous work conducted by MIT and Intel researchers. It offers the promise for automobile electric vehicles and mobile consumer electronic devices to be wireless charged efficiently and safely. For the first time, a wireless charger prototype based on this technology is presented in this paper. Schematics and design considerations are also discussed. Experimental results show that this prototype can wirelessly charge a NOKIA cell phone over a distance 40cm with an input power of less than 4 watt, and has an efficiency of 52% over a 32cm distance.

Wireless charger prototype based on strong coupled magnetic resonance

We present herein for the first time the physical pictures of wireless power transfer via evanescent fields. Our results show that the evanescent fields store energy in a localized domain and can exchange energy between two modes through evanescent waves. We also show that the energy transfer efficiencies can be greatly improved when long-tailed slowly-evanescent fields are adopted. We investigated the energy transfer efficiency and performance of wireless power transfer systems in detail and established their relationship with respect to the coupling strength and the output load parameters. Our theoretical analysis and computer simulations show that the work, radiation and absorption efficiencies are monotone functions of the coupling strength for a given output load parameter and there exists a global optimal output load configuration and a global optimal transfer rate for a fixed coupling strength parameter. The effectiveness, robustness and safety of this class of systems are also verified via the derivation of asymptotic behaviors of the optimum solutions.

Zheng Geng

Papers

Wireless charger prototype based on strong coupled magnetic resonance

Physical Pictures and Performance Analysis of Wireless Power Transfer via Evanescent Fields