Maximum efficiency tracking is an important issue for wireless power transfer (WPT) system. Traditional maximum efficiency tracking method normally focuses on load impedance matching with fixed coupling condition. However, WPT system is a loosely coupling system, the coupling coefficient varies due to relative movement between the primary and secondary sides. Unknown to this variation may result in failure of the tracking. In this paper, a novel maximum efficiency tracking method is proposed with integrated dynamic coupling coefficient estimation. This method can take almost all requirements for maximum efficiency tracking into account including adaption for coupling coefficient and load variation, and output controllability. The tracking method is easy to implement because no additional circuitry or measurement is required. Experimental results have verified the correctness of the proposed coupling coefficient estimation method. And the maximum efficiency tracking results show the system can achieve a good performance against coupling coefficient and load variation with the proposed tracking method.

Dynamic wireless power transfer is a promising solution to address electric vehicle range anxiety and to reduce the ca-pacity and the cost of the on-board batteries. In the traditional DWPT system, the mutual inductances among transmitters make the design of compensation networks very complex. Besides, the power null phenomenon and the power pulsation phenomenon cause a fluctuating DC output voltage or current on the receiver side. To address these issues, this paper proposes a new magnetic coupler. Unipolar and bipolar coils are laid alternately to form segmented transmitters, which are turned ON or OFF according to the position of the overhead receiver coil. LCC compensations, whose inputs are connected in parallel to a common inverter for cost reduction, are adopted. At the receiver side, unipolar and bipolar coils are overlapped in the same plate in order to effec-tively smooth out the mutual inductance variations and hence, reduce the output voltage or current fluctuations. Also, a con-figurable resonant circuit is designed on the receiver side to achieve constant voltage (CV) charging and constant current (CC) charging. Moreover, an optimization design by using Fi-nite-element analysis software Maxwell is developed to choose the best turns of the receiver coil to further improve the output quality. A laboratory prototype with 4-A charging current and 96-V charging voltage, using 85kHz operation frequency, is con-structed to verify the proposed DWPT system. The experimental results show that constant output voltage and current can be achieved within 2% fluctuation, and the overall efficiency is 90.37%.

Current imbalance in multistring light-emitting diodes (LEDs) is a critical issue. It may cause overcurrent in one or more LED strings, leading to rapid degradation. In this paper, a mixed high-order compensation networks-based wireless power transfer system is proposed to generate multiple constant current outputs. It is composed of an LCC resonant network in the transmitting side, a series resonant network, and multiple CLC resonant rectifiers in the receiving side. The CLC resonant rectifiers are connected in parallel to form multiple independent output channels, and each channel is then connected to an LED string. Based on the analysis of the T resonant circuit and the modeling of coupling coils, multiple constant output currents can be derived. As a result, current balance can be achieved, which is very suitable for driving multistring LEDs. The proposed system also offers a modular, scalable, and maintenance-free design, which can significantly reduce the construction cost and the control complexity. In addition, the inverter in the transmitting side can achieve zero phase angle. A laboratory prototype with dual independent output currents is built to verify the proposed method. The experimental results agree well with the theoretical analysis.

A new parallel transmission method of power and data is proposed for peer-to-peer wireless power transfer (WPT) systems. Essentially, data are modulated and transferred via high-frequency electric field generated by the parasitic capacitances of the coupling coils and the metal shield plates, while power is transferred through relatively low-frequency magnetic field generated by the coupling coils. Coupling structure and operation principle are illustrated and analyzed. Besides, the signal to noisy ratio performance is studied and optimized. With the proposed method, a 40 W prototype is built and the data transmission rate reaches 230 kbps. Experimental results have verified that the proposed method is valid and has the advantages of good flexibility and large spatial position offset redundancy. Because the method does not do any modification on the main circuit of the WPT system, it also has advantages of low cost and easy to implement.

In this letter, a new coupling structure for dynamic wireless power transfer (DWPT) systems is proposed. Bipolar coils are symmetrically placed on the transmitter unipolar coils, resulting in natural decoupling between the bipolar coils and the unipolar coils. This special structure can mitigate the self-couplings between the adjacent unipolar transmitter coils and hence, facilitate the design of the compensation circuit. Another remarkable advantage of this design is that it can lead to a stable mutual coupling between the transmitter array and the receiver when the receiver moves along the transmitter, making it a natural fit for DWPT applications. Furthermore, to reduce the electromagnetic interference (EMI) and power loss, an automatic segmented control scheme is implemented, and a position detection method by monitoring the primary current is developed. The feasibility of the proposed coupling structure and the position detection method are verified on a laboratory prototype with 72V output voltage. The experimental results show that, the power fluctuation is within ±2.5%, and system efficiency is around 90%. (This letter is accompanied by a video demonstrating the experimental test).

In this paper, a robust wireless power transfer system is proposed with self alignment capability and controllable output current characteristics for static charging of automatic guided vehicles (AGVs). A reconfigurable circuitry is designed to work initially in an inductor-capacitor-capacitor-series (LCC-S) compensation mode for achieving magnetic field self alignment, then switched to an LCC-LCC configuration for wireless charging. Apart from the passive components used for wireless power transfer, no additional components such as cameras, sensors, or dedicated sensing coils are needed for self alignment. The induced voltage of a series tuned Q-coil on the load side is used for the AGV to automatically adjust its position. The vehicle will be self aligned when the induced voltage becomes null, then the system is switched to a controllable constant current (CC) charging mode. A prototype is built which demonstrates that the output charging current is controllable and can be kept constant against load variations. The experimental results show the proposed system can realize an 89.1% dc-dc power transfer efficiency (PTE) at an output current of 30A and output voltage of 48V.