Jeff Po Wa Chow

Use of primary-side information to perform online estimation of the secondary-side information and mutual inductance in wireless inductive link

It is well-known that the power transfer efficiency of wireless inductive link depends on factors including the mutual inductance between the primary and secondary coils, quality factors of the coils, and resonant tank components. It is thus advantageous to have the real-time information about the aforesaid factors, in order to determine the optimal operating frequency and monitor the load condition. This paper will present a technique that utilizes the primary-side electrical quantities to perform real-time estimation of the mutual inductance, value of the secondary-side resonant capacitor, and electrical quantities on the secondary side. The technique can be applied to three scenarios: 1) with unknown value of the secondary-side resonant capacitor and known secondary-side voltage, 2) with known value of the secondary-side resonant capacitor and unknown secondary-side voltage, and 3) unknown value of the secondary-side resonant capacitor and unknown secondary-side voltage. Detailed mathematical treatment will be given. An experimental prototype using planar transformer has been built and evaluated on a test bed. This technique is also implemented as a control scheme of a cascaded converter to regulate the output power. Experimental results are found to be in close agreement with the theoretical predictions.

An Investigation Into the Use of Orthogonal Winding in Loosely Coupled Link for Improving Power Transfer Efficiency Under Coil Misalignment

It is sometimes unavoidable to use loosely coupled coils in applications, like biomedical devices, for transferring electric energy wirelessly. However, coil misalignment causes degradation of the power transfer efficiency. It is well known that the power transfer efficiency of classical parallel coils is primarily determined by the quality factors of the coils and the coupling coefficient between the coils, and is maximized by choosing an optimal turns-ratio between the coils. Changing the number of turns of the coils cannot effectively overcome such misalignment effect. This paper presents a structure that comprises two orthogonally placed windings for lessening the variation of the coupling coefficient due to the coil misalignment. An output current summing technique that keeps the windings concurrently energized and combines the output currents of the windings will be studied. A canonical model will also be derived to describe the interactions between the coils. An experimental prototype has been built and evaluated on a test bed, which allows different degrees of lateral and angular misalignments. Results reveal that the proposed structure can effectively increase the minimum efficiency zone, allowing more lateral and angular misalignments. These investigations lay the foundation for future understanding more complex loosely coupled winding structures.

Misalignment tolerable coil structure for biomedical applications with wireless power transfer

Coil-misalignment is one of the major hurdles for inductively coupled wireless power transfer in applications like retinal prosthesis. Weak magnetic flux linkage due to coil misalignments would significantly impair the power efficiency. A novel receiver configuration with high misalignment tolerance is presented in this paper. The proposed receiver is composed of two receiver coils placed orthogonally, so as to reduce the variation of mutual inductance between transmitting and receiving coils under misalignment conditions. Three different receiver coil structures are analyzed and compared using the same length of wire. Theoretical predictions have been confirmed with measurement results.

Use of Transmitter-Side Electrical Information to Estimate Mutual Inductance and Regulate Receiver-Side Power in Wireless Inductive Link

It is well-known that the power transfer efficiency and the power transmitted over a wireless inductive link are significantly affected by the strength of the magnetic coupling and the spatial displacement between the transmitting and receiving coils. Misalignment between the transmitting and receiving coils is practically unavoidable. In order to control and regulate the receiver-side power, on-the-spot measurement of electrical quantities and establishment of communication link between the transmitter and receiver are typically required. This paper will present an investigation into the use of the transmitter-side electrical information to estimate the mutual inductance and regulate the power consumption of the receiver side. The nonlinear input voltage-current characteristics of the diode-bridge rectifier, which causes current distortions in the system, are taken into account in the mathematical formulations. The proposed technique is successfully implemented on a 4-W wireless-powered LED driver prototype. Experimental results reveal that the LED power can be regulated within ±25% spatial misalignment over the operating zone. The estimated mutual inductance is also found to be in close agreement with the theoretical predictions.

Online regulation of receiver-side power and estimation of mutual inductance in wireless inductive link based on transmitter-side electrical information

It is well-known that the power transfer efficiency and the power transmitted over a wireless inductive link are significantly affected by the strength of the magnetic coupling and the spatial displacement between the transmitting and receiving coils. Misalignment between the transmitting and receiving coils is practically unavoidable. In order to control and regulate the receiver-side power, on-the-spot measurement of electrical quantities and establishment of communication link between the transmitter and receiver are typically required. This paper will present an investigation into the use of the transmitter-side electrical information to estimate the mutual inductance and regulate the power consumption of the receiver side. The nonlinear characteristics of the diode-bridge rectifier are taken into account in the mathematical formulations. The proposed technique is successfully implemented on a 4W wireless-powered LED driver prototype. Experimental results reveal that the LED power can be regulated within ±25% spatial misalignment over the operating zone. The estimated mutual inductance is also found to be in close agreement with the theoretical predictions.

Design of a wireless power transfer system for devices carried by a freely moving animal in cage

Techniques of long-term in-vivo electrophysiological recording play important roles in brain research and neural rehabilitation. To avoid interruption of experiment and risk of infection, use of wireless power transfer (WPT) technique has recently been suggested to eliminate cumbersome wires and batteries attached to the animals in rodent electrophysiological applications. This paper presents a holistic assessment of the relationships among the physical sizes of the transmitting and receiving coils, power transfer characteristics, and specific absorption rate (SAR) in animals of a simple WPT system using two rectangular coaxial transmitting coils. A 100mW prototype with an operating zone of 400 × 240 × 40mm3 and a receiving coil with a diameter of 11.45mm is built and studied. The SAR in the animal is evaluated and compared with the recommended restriction level.

Impedance-based stability criterion for multiple offshore inverters connected in parallel with long cables

In this paper, the stability study of a multiple offshore parallel long-cable-connected inverters (MOPLI) systemhs has been presented. It is shown that, since this MOPLI system is consisted of a large number of different inverters and long cables, its stability assessment actually faces big challengs. In addition, though there are lots of existing impedance-based stability criteria about prallel inverters, most of them are based on two assumptions: all the inverters are the same and the impacts of the cables can be ignored. However, the above two assumptions are not established in the real MOPLI system. In order to solve this problem, this paper first rederive the models of the inverters and long cables one by one. Based on the rederived models, a general and concise three-step impedance-based stability criterion has been proposed for the MOPLI system. The proposed criterion is not only simple and practicable, but also fully takes account of the inverters difference and the impacts of the cables. Finally, the effectiveness of the proposed criterion has been validated by a 4.9 kW MOPLI system, which is composed of 3 totoally different inverters & non-negligible cables.

Use of Transmitter-Side Electrical Information to Estimate System Parameters of Wireless Inductive Links

The power transfer efficiency and power transfer characteristics of wireless inductive links are determined by several intrinsic and extrinsic factors, such as coupling coefficient, quality factors, matching conditions of the transmitting and receiving coils, and operating frequency. The nominal component values, such as the capacitors used in matching the coils, are chosen by considering the optimal power transfer efficiency and power transfer requirement at the nominal operating condition. However, due to manufacturing tolerance, temperature effect, and aging, electronic components are subject to parameter variations. Such unavoidable issue would cause performance degradation of the link. Typically, it is tackled by conducting on-the-spot measurements of the electrical quantities together with sophisticated communication links and protocols to provide the transmitter with the operating condition of the receiver. To reduce system complexity, this paper presents another perspective by processing transmitter-side electrical information with an evolutionary computation technique to estimate several system parameters, including coil inductances and quality factors, resonant frequencies of the transmitting and receiving networks, and coupling coefficient, for the transmitter to manage power transfer. The proposed technique has been applied to a 4-W wireless-powered LED driver prototype for regulating the load power under parametric variations.

Modeling and experimentation of loosely-coupled coils with transmitter having orthogonally-placed windings

It is sometimes unavoidable to use loosely-coupled coils in applications, such as biomedical devices, for transferring electric energy wirelessly. However, coil misalignment would cause unwanted degradation of the power transfer efficiency. A coil structure that consists of two orthogonally-placed windings in the transmitter is investigated in this paper. Such structure lessens the variation of the coupling between the transmitting and receiving coil sets under the misalignment situations. A driving mechanism for maximizing the power transfer efficiency will be discussed. An experimental prototype has been built and evaluated under lateral and angular misalignments. Experimental results confirm the merits and are in close agreement with the theoretical predictions.

Modeling and experimentation of misalignment-tolerable loosely-coupled coil structure

The misalignment of the transmitting and receiving coils in a wireless inductive link can degrade the link efficiency and limit the amount of power transfer. A coil structure, which is composed of two orthogonally-placed windings for the receiver, will be presented. Such structure lessens the variation of the coupling between the transmitting and receiving coils under coil misalignment. A canonical model for describing the interactions between the transmitting and receiving coils will be firstly presented and then applied to model the entire coil structure. An experimental prototype has been built and evaluated on a test bed under lateral and angular misalignments. Experimental results are found to be in close agreement with the theoretical predictions.