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.

This article identifies how constant voltage load characteristics cause inductive power transfer systems to exhibit a poorly damped oscillation mode. When operated with pulse skipping strategies such as pulse density modulation (PDM), the skipped voltage pulses can excite this mode and cause severe oscillations that do not appear in systems with a constant resistance load. The critical mode is identified from a linearized state-space model of the system and two control approaches are proposed for attenuating the oscillations in current amplitude and power flow. First, the influence of the operating frequency on the critical eigenvalue is analyzed and it is shown how slightly off-resonant operation can increase the damping of the oscillation mode. Second, an active damping method based on sending current feedback control is studied. The active damping is based on phase shift modulation with limited phase shift angles applied to the PDM signal when oscillations are detected. The effectiveness and feasibility of the proposed methods are validated by simulations and experimental results from a small-scale laboratory prototype.

The three level converters have an inherent problem of the neutral point (NP) voltage unbalance due to the split dc-link capacitors. This NP voltage unbalance degrades the output voltage/current waveform quality. A carrier based discontinuous pulse width modulation (CB-DPWM) with NP voltage balancing strategy- that involves the injection of calculated zero-sequence voltages to the original modulation signal - is implemented for the three level T-type converter in this paper. The zero-sequence voltages are determined from the space vector synthesis of the converter output voltages. This method allows the determination of the zero-sequence voltages with few judgment conditions. Unlike the space vector based discontinuous pulse width modulation (SVB-DPWM), the CB-DPWM is easier to realize in practical applications. Moreover, the proposed CB-DPWM can also be directly used in parallel systems, which can suppress NP voltage ripples and circulating currents simultaneously by a coordinated strategy. The efficacy of the proposed method in balancing the neutral point voltage in single and parallel systems is demonstrated by simulations and experiments.

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.

This letter proposes a conditional pulse density modulation (PDM) method for inductive power transfer (IPT) systems, which can automatically adapt the generated output patterns to effectively suppress current/power ripples. The proposed conditional PDM introduces a sending current limitation as an additional condition to skip pulses, which modifies the output patterns generated by conventional delta-sigma-based PDM. Thus, the PDM pulse pattern is continuously adapted to attenuate any excited current/power oscillations. The presented modulator is simple to implement and well-suited for IPT systems with poorly damped constant voltage load characteristics. Simulations and experiments demonstrate the effectiveness of the proposed modulation method.

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.