The wireless power transfer (WPT) system has been extensively studied for its safety, convenience and aesthetics, and has gradually been introduced into our life applications. In order to maintain battery performance, constant current (CC) and constant voltage (CV) charging outputs are generally regarded as the dominant charging modes. However, battery equivalent resistance changes significantly during the charging, so it is difficult to simultaneously achieve load-independent CC and CV charging outputs and zero phase angle (ZPA) condition. This paper proposes a new LCCC/S topology and its corresponding parameter tuning method to obtain CC and CV charging modes at two different ZPA operating frequency points, respectively. In addition, it is worth mentioning that the receiver has only one compensation capacitor, which follows the principle that the receiver of the WPT system should remain compact and portable. Furthermore, a simple frequency modulation controller is designed to solve the problem of inaccuracies of the charging outputs due to parasitic losses of components and fluctuations of DC input voltage. Finally, a verification setup with 3A output current in CC mode and 48V output voltage in CV mode was built to validate the feasibility and rationality of the proposed LCCC/S compensated WPT system and the corresponding control method.

The wireless power transfer (WPT) system has been gradually integrated into our daily applications due to its advantages of security, esthetics, and convenience. Generally, for a complete WPT system, two main goals need to be achieved: one is the constant voltage (CV) output and the other is the highest possible transfer efficiency. However, the highest possible transfer efficiency is difficult to achieve when the WPT system maintains the CV output against the time-varying load resistance and coupling coefficient. In this article, a new dual-side control scheme that employs transmitter-side high-frequency inverter (HFI) and receiver-side semi-active rectifier (SAR) is proposed to simultaneously achieve the CV output and maximum efficiency tracking (MET) control regardless of the variable load resistance and coupling coefficient. It is proved that the system can obtain the maximum transfer efficiency when the derivative of $\sin (\alpha /2)$ with $\sin (\beta /2)$ is a specific constant, which is determined by self-resistances of transceiver coils and system input and output dc voltage. In the above derivative, $\alpha $ and $\beta $ are phase shift angles of the HFI and SAR, respectively. The CV output is maintained by adjusting $\beta $ , while the MET control is performed by continuously adjusting $\alpha $ . A confirmatory experimental setup with the charging voltage of 72 V is built, and the experimental results fully prove the correctness and effectiveness of the proposed scheme.

Compared with the traditional plug-in charging system, the wireless charging system for battery charging has broad application prospects due to its significant advantages such as security, convenience and aesthetics. In practical applications, in order to prolong the battery lifecycles, it is preferred to charge the battery with constant current (CC) and constant voltage (CV) modes. However, since the battery equivalent resistance varies greatly during charging, it is not easy to design a complete charging system owning CC and CV output characteristics. Besides, the equivalent input impedance of the system is preferably resistive to improve efficiency and enhance power transfer capability, so achieving the zero phase angle (ZPA) operation is extremely important. Hence, a novel three-coil structure WPT system is proposed in this paper to solve the above issues. A comprehensive theoretical analysis for the three-coil system to realize the CC and CV charging modes with perfect ZPA operation at two fixed operating frequencies is presented. Furthermore, due to the parasitic losses of passive components and the instability of the dc input voltage, it is unrealistic to achieve accurate and stable CC and CV outputs through the inherent properties of the circuit itself. Consequently, a simple closed-loop controller is introduced into the system to enable the desired CC and CV charging characteristics with zero voltage switching (ZVS) operation by slightly adjusting the operating frequency. Finally, a confirmatory experimental prototype with 4.6 A charging current and 56 V charging voltage is fabricated to confirm the feasibility and validity of the proposed method. The experimental results agree well with the theoretical analysis.

Wireless power transfer (WPT) is a promising energy transfer method for its security, reliability and convenience, and has been applied in various scenarios. In practical applications, in order to prolong the battery lifecycles, the WPT system preferably has the load-independent constant current (CC) and constant voltage (CV) charging characteristics and zero phase angle (ZPA) operation for high power transfer efficiency. However, since the equivalent resistance of the battery significantly changes over the entire charging process, it is difficult to design a WPT system with the above functions. This manuscript proposes a S/S/P-compensated three-coil structure WPT system and its corresponding parameter tuning method to achieve CC and CV charging modes at two different ZPA operating frequencies. For the proposed three-coil structure WPT system, since only one compensation capacitor is required on the receiver, the compactness and portability of the receiver of the WPT system are guaranteed. Firstly, the comprehensive theoretical analysis for the CC and CV charging modes and ZPA operation is presented, and the detailed parameter design method of the proposed system is provided. Secondly, the sensitivity of variations in system parameters to CC and CV characteristics is analyzed, and the implementation of ZVS operation for further improving efficiency is introduced. Thirdly, a confirmatory experimental prototype with charging current of 4.6A and charging voltage of 56V is fabricated, and the experimental results are basically consistent with the theoretical analysis. Finally, a comprehensive comparison with previous WPT systems of the same type is carried out to highlight the superiority of the proposed three-coil structure WPT system.

In this paper, a novel long-distance wireless power transfer (WPT) system which achieves excellent constant current (CC) output based on Domino-Resonator is proposed. A thorough mathematical model of n-coil domino WPT system is established and the methodology of calculating and choosing the operating frequency in CC mode is put forward to achieve high efficiency and the best stability. Zero phase angle (ZPA) condition is proved to be realized in the meantime by theoretical derivation. The phenomenon that operating frequency slightly shifts away from the resonant frequency in CC mode due to the magnetic coupling between nonadjacent coils is studied. And the efficiency of the system is evaluated. Moreover, system efficiency can be further improved by optimizing number of the coils and layers when the transfer distance is fixed. An experimental setup with the output current of 0.6 A has been built to demonstrate the validity of the proposed system. The experimental results show that the maximum system efficiency of the experimental setup in CC mode can achieve 70% at the transfer distance of 0.7 m when the number of the coils is 8 and the radius of the coil is 100 mm.

In some practical applications such as battery charging and LED driving, it is desirable for the WPT systems to have load-independent constant current output (CCO) characteristic. However, the existing WPT systems with CCO function suffer from low efficiency, limited output current by the loosely coupled transformer (LCT) parameters, low space utilization and high cost. In order to solve the above issues, this manuscript proposes a new integrated LCC/S WPT system with CCO function, in which the transmitter-side compensation inductor and the transmitter-side coil are coaxially and symmetrically stacked on the same plane to save the space occupied when they are placed separately in the traditional structure. A detailed mathematical derivation of the proposed integrated LCC/S WPT system with both load-independent CCO characteristic and zero phase angle (ZPA) operation is carried out, and the explicit corresponding parameter design method is provided. It is worth emphasizing that the output current of the proposed integrated LCC/S WPT system is not limited by the LCT parameters due to sufficient design freedom. Then, a comprehensive theoretical analysis on the realization of zero voltage switching (ZVS) operation for higher overall efficiency and the impact on the CCO characteristic by slightly adjusting the parameters of the compensation capacitors is performed. Furthermore, a detailed and thorough efficiency comparison between the proposed integrated LCC/S WPT system and the SS WPT system is performed under alignment, long-distance and misalignment conditions to reflect the efficiency advantage of the proposed system. Finally, a demonstrative experimental prototype with 60-V DC input voltage and 4.9-A CCO is fabricated to validate the correctness and rationality of the proposed integrated LCC/S WPT system and the corresponding theoretical analysis.