Wireless power transfer (WPT) is the preferred charging method for electric vehicles (EVs) powered by battery and supercapacitor. In this paper, a novel WPT system with constant current charging capability for sightseeing car with supercapacitor storage is designed. First, an optimized magnetic coupler using ferrite cores and magnetic shielding structure is proposed to ensure stable power transfer and high efficiency. Compared with the traditional planar shape ferrite core coupler, the proposed magnetic coupler requires lesser ferrite material without degrading the performance of the WPT system. Second, the model of supercapacitor is applied to the WPT system and the relationship between equivalent load resistances of supercapacitor and charging time is analyzed in detail. Then, a Buck converter with proportional integral (PI) controller is implemented on the secondary side to maintain constant charging current for the variable load. Finally, the proposed design is verified by experiments. Constant charging current of 31.5 A across transfer distance of 15 cm is achieved. The peak transfer power and system efficiency are 2.86 kW and 88.05%, respectively.

This paper proposes a new control technique, which only employs the primary-side controller and load identification approach to adjust the charging voltage/current for both series-series (SS) and series-parallel (SP) compensated wireless power transfer (WPT) systems. The advantage is that dual-side wireless communication for real-time charging current/voltage adjustment is avoided as well as it is suitable for different charging modes, e.g. constant voltage (CV) and constant current (CC) charging defined by the battery charging profile. The load identification approach, which utilizes the reflected impedance theory and quadrature transformation algorithm for calculating the active power, is proposed to estimate the equivalent load resistance. Then, the CV/CC charging for both SS and SP compensation are achieved by PI controlled phase shift H-bridge inverter. The simulation and experimental results validate the feasibility of the proposed method. During the CC charging, the 3.01A and 3.03 A for SS and SP compensation with the error of 1.2% and 1.4% are achieved. During the CV charging, the 25.8 V and 25.7 V for SS and SP compensation with the error of 1.1% and 1.3% are realized. The proposed method improves the performance of both SS and SP compensated WPT systems to be more suitable for the applications that require compact and light weight receiver.

Charging current and efficiency of a wireless power transfer (WPT) system depend on the equivalent load resistance of supercapacitor load, which varies during charging. To achieve constant current (CC) charging and maximized efficiency under variable loads, control method that uses primary-side phase shifted H-bridge inverter and secondary-side semi-active rectifier are proposed. The secondary-side control method not only achieves CC charging, but also ensures no reactive impedance seen into the semi-active rectifier. On the other hand, the maximum efficiency tracking is based on searching the minimum system dc input current for any given output power and realized by the phase shifted H-bridge inverter controlled by the perturbation and observation algorithm. Experiments are performed to validate the feasibility of the proposed control method. During CC charging of 3 A, the maximum efficiency is 81% and the largest efficiency improvement is 15.2% at light load. The proposed method improves the system performance and is suitable for practical applications that require compact receiver and no wireless communication link between the transmitter and the receiver.

To prevent magnetic flux leakage to the maximal extent, increase the coupling coefficient of high-power inductive power transfer (IPT) system, and reduce the electromagnetic radiation in water medium, a novel underwater loosely coupled transformer (LCT) based on the semiclosed magnetic core structure is proposed in this paper. Power loss of the devised LCT is investigated comparatively in three media including air, freshwater, and seawater. It is shown that winding loss and core loss in the three media are basically identical. However, additional eddy current (AEC) loss in various water media is different for the sake of the difference in conductivity. In particular, AEC loss is extremely low in freshwater and relatively significant in seawater. Furthermore, when the operating frequency exceeds a certain value, AEC loss will be greater than core loss and winding loss, and become the major factor in restricting transmission efficiency of LCT in seawater. Finally, theoretical analysis and simulation are demonstrated by the underwater experiment on an IPT prototype system, which can transfer 10 kW at 91% maximal transmission efficiency and over a 25 mm air gap.