The mass of a magnetic coupler increases with the output of its wireless power transfer system, limiting broader application of this technology. It is imperative to solve this trade-off between output power and coupler mass. Here, we present a high-power-density wireless power transfer system designed for autonomous underwater vehicles (AUVs) based on a variable ring-shaped magnetic coupler. A lightweight design is achieved through the system topology and magnetic coupler structure, and the system parameters are optimized and analyzed. Our magnetic coupler can eliminate the gap between the AUV and the platform when charging and fix the posture of the AUV to improve the system power output and stabilize the transmission process. An 800 W prototype was built, and manipulation of the variable ring-shaped magnetic coupler maintained the DC-DC transmission efficiency of the system at 86.4% and increased the output power by 69.47 W, or 9.1%. With these improvements, the system power density reached 1.6 W/g after using the variable ring-shaped magnetic coupler, realizing an increase of 9.6%. Experimental results validate the theoretical analysis and simulation outcomes to prove the effectiveness of this new method.

Comprehensive research on the wireless power transfer technology of autonomous underwater vehicles is necessary to address the issue of significant energy loss in such vehicles during wireless power transfer. Previous analysis on factors that affect wireless power transfer in seawater environment demonstrated that the eddy current loss generated during transmission and offset of the coupling mechanism are the main factors that degrade the efficiency. In this study, existing literature on wireless power transfer for autonomous underwater vehicles in recent years is reviewed, and it is concluded that the energy loss during underwater wireless power transfer can be effectively reduced through coupling mechanism optimization, adaptive control, and docking device design. This study analyses the challenges of low‐loss wireless power transfer for autonomous underwater vehicles and the prospects for future development trends and research areas, providing a reference for realizing efficient and flexible energy supply for autonomous underwater vehicles.

Combining wireless power transfer (WPT) technology with an underwater inclusive charging platform is an effective method to solve the problem of energy replenishment for autonomous underwater vehicles (AUVs). To ensure a stable charging state of the AUV at arbitrary positions, an antirotation flexible magnetic coupler (FMC) is proposed in this article. The transmitter structure can follow the retractable cage changes of the charging platform. Through the optimization analysis, the FMC, composed of a single-layer transmitter coil and a double-layer receiver coil and rotated 45° between the two layers of receiver coils, has excellent antirotation capability under 360° rotations. Moreover, the magnetic field of the FMC is evenly distributed and concentrated between the magnetic cores of the transmitter and receiver, causing little effect on the equipment inside the AUV. To address the coupling parameter variations due to AUV rotation and the transmitter contraction during FMC operation, soft switching of the WPT system is achieved by pulse density modulation and slight detuning of the resonator. An experimental prototype was established to verify the antirotation characteristics of the FMC as well as the soft-switching attributes of the system, and the experimental results matched well with the simulations.

Nanocrystalline magnetic cores have been applied in inductive power transfer (IPT) systems as novel magnetic materials for their high saturation capability and flexible application. However, the loss of eddy current is still a primary concern in nanocrystalline material. This letter investigates two crushing patterns, namely square-crushing and dot-crushing, for nanocrystalline flake ribbon (NFR) to mitigate the eddy current loss in IPT applications. In the experiment, a 1 kW IPT prototype with a curved coupler for autonomous underwater vehicles (AUVs) is built to verify the loss performance. As a result, the coil with NFRs in the square-crushing pattern (S-pattern) has a higher quality factor than those with the NFRs in the dot-crushing pattern (D-pattern). Furthermore, the IPT system with S-pattern NFR exhibits an AC-AC transmission efficiency of 93.51%, possessing 0.89% higher than that of the D-pattern NFR case. The utilization of the S-pattern NFR offers multiple benefits, including minimizing core loss and facilitating the advancement of IPT systems with increased power density and enhanced installation flexibility.

When autonomous underwater vehicles (AUVs) replenish energy through wireless power transfer (WPT) technology on the underwater charging platform, there are practical issues such as excessive transmission gaps and unstable positioning. Additionally, the fixed size of the charging platform leads to insufficient compatibility. This paper proposes a high compatibility WPT system based on a reconfigurable magnetic coupler (RMC) for AUVs replenishing underwater energy. The transmitter of the RMC is combined with the charging platform cage and can follow the charging platform cage in radial dimensions. RMC can provide better coupling performance, and its necessity and effectiveness have been verified through finite element simulation. When the proposed high-compatibility charging platform supplies energy to AUVs of different sizes, the RMC will reconfigure its structure, leading to changes in the transmitter's self-inductance. To address this issue, a switch-controlled capacitor (SCC) method was incorporated into the system to achieve dynamic tuning. Finally, an experimental prototype was built to test the functionality and performance of the proposed RMC structure and SCC method. Compared to existing methods, this approach significantly enhances the practical application capabilities of WPT technology in underwater charging platforms and positively contributes to the cluster deployment of AUVs.

The classical Cuk, Sepic, and Zeta converters have found wide applications in various fields. However, there has been limited research exploring their relationships. This letter aims to uncover their relationships by focusing on their capacitor-less circuits (CLCs). Initially, it is observed that these three converters exhibit highly similar performance characteristics, such as equal voltage gains and average component currents. Subsequently, this letter establishes that their equivalent CLCs are the reason behind these similarities, presenting a new perspective on understanding dc-dc converters with capacitors. Furthermore, based on the above findings, a novel topology derivation method is proposed by connecting capacitors to a CLC. Compared with the traditional methods, the proposed method can derive families of converters with comparable performance. Moreover, the proposed method is particularly suitable to leverage existing converter designs and modify them to meet specific requirements. The proposed method successfully derives several groups of converters from different CLCs. For a group of converters derived from an equivalent CLC, their effectiveness and their performance relationship are verified experimentally.