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%.

Traditional wireless power transfer (WPT) systems usually adopt the single-phase-shift (SPS) control method to maintain a constant output current or a constant output voltage for various applications. However, the current-stress on one side is much higher than that of the other side especially under operating conditions with high voltage conversion ratio and light-load. This phenomenon actually can be proven by the established mathematical model of the current-stress of WPT systems using SPS control. This large current-stress will damage power devices and lower the efficiency of WPT systems. In addition, it will result in an increase of system total cost because of the need for the devices with the higher volt-ampere rating. A control strategy based on dual-phase-shift control is developed for WPT systems with an active rectifier to reduce the maximum value of current-stresses on both sides as well as to maintain a constant output voltage or current. Consequently, the system efficiency can be improved compared to traditional WPT systems with SPS control. A scaled-down experimental prototype is constructed to verify the effectiveness of the proposed WPT topology and the control method. Experimental results show that the proposed method can reduce the maximum current-stress significantly and improve the system efficiency compared to traditional WPT systems under SPS control.

The design of operating frequencies and compensation topologies for load-independent output current or output voltage in two-coil wireless power transfer (WPT) system has been widely studied. The three-coil WPT system has been proven to be more efficient and shows a better performance compared to the two-coil WPT system with an increasing transmission distance. However, the research on load-independent output voltage or output current of the three-coil WPT system is still at pilot stage. This paper systematically investigates the load-independent output voltage and output current characteristics of a three-coil WPT system to achieve a constant output voltage (CV) and constant output current (CC) with near zero reactive power, which can simplify the control. The CV and CC characteristics are achieved by welldesigned passive parameters of the receiver side compensation. Additionally, a hybrid receiver side compensation with two additional switches for the three-coil WPT system is developed to charge the electric vehicle (EV) battery by combining the CC and CV characteristics. Finally, a scaled-down experimental setup with 4A charging current and 96V cell voltage is constructed to verify the proposed approach. The experimental results agree well with the theoretical analysis.

To maintain a stable output voltage under various operating conditions without introducing extra DC/DC converters, phase-shift (PS) control is usually adopted for wireless power transfer (WPT) systems. By using this method, however, zero voltage switching (ZVS) operation cannot be guaranteed, especially in light load conditions. To achieve high efficiency and reduce electromagnetic interference (EMI), it is significant for WPT systems to achieve ZVS operation of all switching devices in the whole operation range. In this paper, an auxiliary variable inductor (VI), of which the equivalent inductance can be controlled by adjusting the DC current in its auxiliary winding, is designed for series-series compensated WPT systems under PS control to mitigate the loss arising from hard switching. As a result, a wide ZVS operation range of all switching devices can be achieved. A laboratory prototype is built to verify the theoretical analysis. The experimental results show that, under load and magnetic coupling variations, ZVS operation at fixed operation frequency as well as a constant DC output voltage can be maintained. Compared to the conventional method with only PS control, the proposed WPT can achieve higher overall efficiency in a wider load range owing to the wide ZVS operation range.

In this letter, a compact battery charger based on wireless power transfer (WPT) technology without any communication requirement is proposed. Here, a new intermediate coil is developed to achieve load-independent constant current (CC) and constant voltage (CV) outputs. The intermediate coil is split into two coils and is overlapped with the receiver coil to form a compact structure. Two switches on the receiver side are used to reconfigure the intermediate resonant circuit in order to select different charging modes, i.e., CC mode or CV mode. The communication between the transmitter side and the receiver side as well as complex control strategies is not needed in the proposed structure. Besides, the proposed system can achieve zero phase angle operation, fixed operating frequency, and zero-voltage switching, which not only can lower the power rating of power devices but also improve the efficiency. A laboratory prototype with a 3.6 A charging current and a 48 V charging voltage is built to verify the feasibility of the proposed method.

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.