In order to improve misalignment tolerance for an inductive power transfer (IPT) system, a third-coil is employed to reversely connect with the primary coil of the loosely coupled transformer (LCT) in series. The LCT with a third-coil (LCT-TC) not only can improve the misalignment performance in x- and y-directions, but also do not affect the inherent output characteristics (such as constant current or voltage output) of original compensation topologies. In addition, the proposed approach can keep the IPT system operating with relatively high efficiency against misalignment. Then, a detailed design method of LCT-TC is presented. Finally, a double-side LCC compensated IPT system is chosen as an example to verify the feasibility of proposed LCT-TC. A 3.4kW prototype is constructed, and experimental results show that the proposed method has good misalignment performance. The LCC-LCC IPT system with LCT-TC can retain 96% of the well-aligned power at 40% misalignment, and the end-to-end (dc-dc) overall system efficiency is at least 92%. Besides, the fluctuation of the output current is [-2%, 5%] while the load varies from 15 Ω to 34 Ω within 40% misalignment.

Wireless power transfer (WPT) chargers for electric bicycles (EBs) have many advantages over transitional plug-in systems. However, to meet the charge requirements, the traditional charger needs a dedicated inverter to achieve constant current (CC) output or constant voltage (CV) output. A hybrid topology based EBs charging strategy is proposed using a single high-frequency inverter (HFI) to charge massive EBs, and one charging stand can be shared to charge EBs with various specifications of batteries. Configurable CC and CV outputs can be realized by turning on/off two AC switches (ACSs) without adopting sophisticated control schemes or wireless communication links. Besides, zero phase angle (ZPA) switching of HFI can be realized, and then the system efficiency is increased. Finally, the proposed method is verified by experiments with various charging conditions. The results show that the fluctuation margins of charging currents and charging voltages in the whole charging process are both less than 2.5% and the maximum efficiency reaches 91.90%. With the merit of the proposed approach, the reduction of construction cost and the control complexity is achieved. Thus, it might be one of the most promising solutions for charging massive EBs in some regions like China.

Electric bicycles (EBs) are becoming increasingly popular in some regions such as China and Europe. However, wireless power transfer (WPT) for charging massive EBs poses a challenge related to the cost of WPT system (WPTS), especially in China, where EBs application is so sensitive to the product price. This paper presents an optimization method of the passive components for the S-LCC topology to decrease the cost of the overall system. With the novel method, the number of passive components can be optimized to the minimum and still with constant current and constant voltage outputs. A novel compensation method with an inductor array is also proposed to guarantee an inductive input impedance of WPTS, achieving soft switching and reducing the high switching losses of the high-frequency inverter (HFI). To demonstrate the validity of the proposed methods, an experimental setup is built. The performance of two WPTS indicates that massive EBs can be charged with only one HFI, and the cost of the overall system decreases accordingly.

The detuning of an inductive power transfer (IPT) system caused by the component tolerance and aging of the inductors and capacitors can decrease the system efficiency, accordingly. To tune the receiver circuit of the IPT system dynamically, an inductor is parallelly connected with a diode full-bridge rectifier cascaded with a buck converter serving as a tuning circuit in this paper. By changing the duty cycle of the buck converter, the impedance of the tuning circuit can be adjusted to compensate the reactance caused by detuning. The tuning range of the proposed method is analyzed in detail. A corresponding control method, in which an auxiliary measurement coil is utilized, is proposed to tune the receiver circuit dynamically while regulating the output voltage. Because the buck converter is with the dc side of the receiver, no synchronization is required for the switches of the buck converter, and the switching frequency of the buck converter can be much lower than the inverter frequency. A 400 W prototype is established to validate the proposed method. The experimental results show that with 15% tolerance of the resonant capacitor in the receiver side, the system efficiency with the proposed tuning method can reach 91% with an improvement by 7.9% compared to the detuned system.

For a traditional 2-coil system outputting constant voltage (CV), the transfer efficiency decreases drastically as transfer distance increases. To solve this problem, this essay proposes a 3-coil system which could achieve CV output and Zero Phase Angle (ZPA) conditions with specific parameter values. This 3-coil system could partly relief transfer efficiency fall at a long transfer distance, without any complicated controls. In order to achieve CV and ZPA condition, this essay devises the parameter values based on the decoupling 3-coil model, and a prototype is designed accordingly to verify these characteristics. With 10 cm transfer distance, output voltage deviation is 5.5% as the load varies from 12 Ω to 200 Ω, proving that the output voltage almost keeps constant with load change. Furthermore, with software simulation, a comparison experiment between the proposed 3-coil system and a Series-Inductor-Capacitor-Inductor (S-LCL) compensated 2-coil system is built to verify the efficiency improvement. The transfer distance change leads to the differentiation of voltage gain for both 2-coil and 3-coil systems. So, the input voltage for both systems and the compensated capacitor in receiver loop of the 3-coil system are manipulated for keeping 60 V output voltage on the 12 Ω load. With distance increasing from 10 cm to 20 cm, transfer efficiency varies from 92.61 to 48.9% for the 2-coil system, and from 92.89 to 84.26% for the 3-coil system, effectively proving the efficiency improvement. The experiment and simulation results prove the effectiveness of the proposed method.