It is more convenient and safer to employ inductive power transfer (IPT) systems to charge the battery pack of electric bicycles (EBs) than conventional plug-in systems. An IPT charging method suitable for charging massive EBs is proposed to achieve constant current (CC) and constant voltage (CV) output without feedback control strategies or communication link between transmitter side and receiver side. Two ac switches (ACSs) and an auxiliary capacitor utilized at receiver side are employed to be operated once to change the charging modes from CC mode to CV mode. The characteristics of the load-independent current output in the CC mode and load-independent voltage output in the CV mode are achieved by properly selecting the passive parameters of inductances and capacitors, so that no sophisticated control strategies are required to regulate the output as per the charging profile. The feasibility of proposed method has been verified with an experimental prototype in form of efficiency, stability of output current and voltage in CC/CV mode. The simple and economical approach is suitable for the massive EBs charging system with only one inverter, especially in China.

Inductive power transfer (IPT) for battery charging applications has significant advantages over the traditional plug-in system. Since misalignment between the primary and secondary windings is inevitable, it is of significance to improve the misalignment tolerance of IPT systems with constant-current (CC) and constant-voltage (CV) outputs for battery charging. In this paper, the load-independent output characteristic of the hybrid topology and the function switching between CC and CV of the reconfigurable topology are analyzed. Besides, a hybrid and reconfigurable IPT system with 3-D misalignment tolerance for CC and CV outputs is proposed, simplifying or even canceling control schemes. Moreover, a novel parametric design method is given for the IPT system, which can suppress the fluctuation of the output voltage/current within a certain range of misalignment. In order to validate the performance of the proposed topology, a 1-kW prototype is built, and the corresponding experiments are carried out. In the CC/CV mode, the system can operate with the longitudinal misalignment to 50% when the load varies from 36 to 480 Ω, and the fluctuation of the output current/voltage is within 5%. Similarly, the misalignment in Y- and Z-axis is 12.5% and 33.3%, respectively.

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.

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.

Pad misalignments are almost inevitable in most inductive power transfer (IPT) systems. It tends to cause parameter variations and thus significantly affecting the performance of the IPT system. In this paper, a hybrid IPT system with misalignment tolerance using quadruple D quadrature pads (QDQPs) is proposed to tolerate x-, y-, z- and diagonal misalignments with load-independent output voltage, simplifying or even canceling control schemes. Besides, the proposed approach can restrict the increase of the primary current when the secondary side moves out of the operating region. Moreover, a new parametric design method is presented according to the misalignment characteristics of QDQPs. The method can limit the output voltage fluctuation to a certain range given a predetermined misalignment distance. A 3.5-kW prototype was built to verify the proposed hybrid IPT system. The primary and secondary coil sizes are both 400 mm×400 mm and the air gap is 150mm. Experimental results demonstrate that the proposed hybrid system can tolerate -150 mm to +150 mm x-misalignment, -150 mm to +150 mm y-misalignment, -20 mm to +35 mm z-misalignment, and -100mm to +100mm diagonal misalignment with load-independent output voltage. Within the predetermined mis-alignment range, the output voltage fluctuation is less than 5%.

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.