Underwater Wireless Power Transfer Research Articles

Wireless Power Transfer for Unmanned Underwater Vehicles: Technologies, Challenges and Applications

Unmanned underwater vehicles (UUVs) are key technologies to conduct preventive inspection and maintenance tasks in offshore renewable energy plants. Making such vehicles autonomous would lead to benefits such as improved availability, cost reduction and carbon emission minimization. However, some technological aspects, including the powering of these devices, remain with a long way to go. In this context, underwater wireless power transfer (UWPT) solutions have potential to overcome UUV powering drawbacks. Considering the relevance of this topic for offshore renewable plants, this work aims to provide a comprehensive summary of the state of the art regarding UPWT technologies. A technology intelligence study is conducted by means of a bibliographical survey. Regarding underwater wireless power transfer, the main methods are reviewed, and it is concluded that inductive wireless power transfer (IWPT) technologies have the most potential. These inductive systems are described, and their challenges in underwater environments are presented. A review of the underwater IWPT experiments and applications is conducted, and innovative solutions are listed. Achieving efficient and reliable UWPT technologies is not trivial, but significant progress is identified. Generally, the latest solutions exhibit efficiencies between 88% and 93% in laboratory settings, with power ratings reaching up to 1–3 kW. Based on the assessment, a power transfer within the range of 1 kW appears to be feasible and may be sufficient to operate small UUVs. However, work-class UUVs require at least a tenfold power increase. Thus, although UPWT has advanced significantly, further research is required to industrially establish these technologies.

Anti-Offset Multicoil Underwater Wireless Power Transfer Based on a BP Neural Network

Autonomous underwater vehicles (AUVs) are now widely used in both civilian and military applications; however, wireless charging underwater often faces difficulties such as disturbances from ocean currents and errors in device positioning, making proper alignment of the charging devices challenging. Misalignment between the primary and secondary coils can significantly impact the efficiency and power of the wireless charging system energy transfer. To address the issue of misalignment in wireless charging systems, this paper proposes a multiple transfer coil wireless power transfer (MTCWPT) system based on backpropagation (BP) neural network control combined with nonsingular terminal sliding mode control (NTSMC) to enhance further the system robustness and efficiency. To achieve WPT in the ocean, a coil shielding case structure was equipped. In displacement experiments, the proposed multi-transmitting coil system could achieve stable power transfer of 40 W and efficiency of over 78.5% within a displacement range of 8 cm. The system robustness was also validated. This paper presents a new AUV energy supply solution based on MTCWPT. The proposed MTCWPT system can significantly improve the navigation performance of AUVs.

Underwater Power Conversion and Junction Technology for Underwater Wireless Power Transfer Stations

Underwater wireless power transfer (UWPT) systems are appropriate for battery charging of compact, submerged devices without a complicated and expensive sealing structure or human contact because the power source and load are not physically connected. For the shore-based power supply situation, the underwater power conversion and junction technology should be required to drop down shore-based voltage to the target voltage for the underwater energy supply of the UWPT system. This paper proposes a lightweight, high efficiency and power density underwater power conversion connector system for the UWPT system, in which the LLC resonant converter is constructed with SiC transistors. The full load range zero-voltage switching (ZVS) and load adaptive characteristics have been achieved. The optimized RC level shift driver is adopted to highly reduce the switching loss of SiC transistors. Shore-based voltage of 1000 V was converted to the target voltage of 375 V for the UWPT system. The highest measured efficiency is over 98% at a load power level of 1500 W underwater conditions.

Experimental Results and Analysis of Midrange Underwater Asymmetric Wireless Power Transfer

The eddy current loss caused by the conductivity of seawater results in a relatively low transfer efficiency of underwater wireless power transfer (WPT). And the transfer distance of the current WPT system is relatively short. Considering that most of the wireless power transfer devices in practical applications are asymmetric, few studies have explored the transfer characteristics of asymmetric midrange WPT in seawater. In this study, it is experimentally found that the load voltage and transfer efficiency of an asymmetric midrange WPT system with reduced primary balancing resistance in seawater are nearly twice as high as those of a symmetric one at a 50 cm transfer distance and a 410 kHz operation frequency with a 44.4 Ω load resistance. A new circuit model of the underwater WPT system with complex impedance and complex mutual inductance is then presented, and the load voltages predicted by the model are consistent highly with the experimental values; the model is then utilized for the explanation of the experimental observations. Changing the load resistance also improves the transfer efficiency of the system; however, the eddy current loss results in a relatively low transfer efficiency of 30.9% at an optimal load resistance of 90 Ω. The asymmetric midrange underwater WPT system can be applied in scenarios where the transfer distance is prioritized.

Design of a Capacitive Coupler for Underwater Wireless Power Transfer Focused on the Landing Direction of a Drone

Design of a Capacitive Coupler for Underwater Wireless Power Transfer Focused on the Landing Direction of a Drone

Six-Plate and Hybrid-Dielectric Capacitive Coupler for Underwater Wireless Power Transfer

Six-Plate and Hybrid-Dielectric Capacitive Coupler for Underwater Wireless Power Transfer

A Survey on Underwater Wireless Power and Data Transfer System

A Survey on Underwater Wireless Power and Data Transfer System

A Novel Pendulum-Type Magnetic Coupler With High Misalignment Tolerance for AUV Underwater Wireless Power Transfer Systems

A Novel Pendulum-Type Magnetic Coupler With High Misalignment Tolerance for AUV Underwater Wireless Power Transfer Systems

Research on Double LCC Compensation Network for Multi-Resonant Point Switching in Underwater Wireless Power Transfer System

This paper introduces a control method suitable for AUVs to transmit underwater radio energy that improves the stability of AUV charging under water based on double LCC compensation. The coupling coefficient decreases with the rise of the coil offset in the underwater wireless power transfer system, such that the power transmission capability is reduced. To solve the above-mentioned problem, a double LCC resonant compensation network impedance characteristic is proposed in this study through the analysis of the double LCC resonant compensation network. To be specific, the wireless power transmission method for multi-resonant point switching of the LCC compensation network is developed. The multiple resonance points of the developed method are not correlated with the load impedance in the double LCC resonance compensation network, and the multiple resonance points are consistent with the power transmission characteristics. Moreover, the appropriate resonance frequency is matched based on different coupling coefficients, and the multi-resonance points are switched to each other to increase the system’s transmission power and transmission efficiency. As revealed by the results of the simulation and experimental studies, the double LCC compensation network with multi-resonance point switching is capable of achieving the output characteristics of constant-voltage/constant-current of the wireless power transfer system, reducing the system current harmonics effectively, and enhancing the power transmission capability and anti-offset capability.

Design of a Highly Compatible Underwater Wireless Power Transfer Station for Seafloor Observation Equipment

Conventional cabled seafloor observatories (CSOs) power in-situ instruments via wet-mated or dry-mated direct electrical contact (DEC) connectors to achieve long-term and real-time observation. However, the DEC connectors have high risks of water leakage and short circuits in power feeding, especially under high water pressure. This paper proposes a highly compatible underwater station based on inductive wireless power transfer (IPT) technology to address the above reliability issue. A novel energy transmitter with runway-structure coils is applied to the proposed underwater station to cover a sufficient power feeding area so that various in-situ equipment can be powered with desirable misalignment tolerance. The magnetic field distribution is analyzed by both derivation and finite element analysis (FEA) methods, and the principal parameters of the transmitter are further optimized and compared with both the mixed-integer sequential quadratic programming (MISQP) algorithm and the evolutionary algorithm (EA) for better performance. The same results show a reliable optimization process. The WPT circuit characteristics are also investigated to power different loads and improve the power transmission efficiency. The output power decreases, and the transmission efficiency rises and then decreases as the load increases. In addition, receivers with higher mutual inductance have better transmission performance. A prototype of the underwater station has been tested both in air and in water, and the experimental results have proven it can power multiple seafloor observation instruments stably and achieve compatibility requirements. The maximum output power of the station prototype for testing is 100 W, and the maximum overall transmission efficiency is 61%.

Bidirectional inductive underwater wireless power transfer converter with variable structure

The undersea sensor networks have an important function in marine resource exploration. To prolong the lifetime of the sensor networks, a bidirectional inductive underwater wireless power transfer (BI-UWPT) system with variable structure is proposed. With the proposed system, the autonomous underwater vehicle (AUV) could receive energy from the undersea docking station and transmit energy to the undersea sensor networks. The two full bridge topologies and the SS compensation networks are adopted in the system to achieve the bidirectional power transfer. To achieve bidirectional energy transmission of different power levels, two different operating frequencies and variable compensation capacitors are employed by the AUV. The system mathematical model is also presented. To verify the theoretical analysis, a 432 W simulation model when the AUV receiving electric energy and a 96 W simulation model when the AUV transmitting electric energy are constructed, respectively. The theoretical analysis is verified by the simulation results. Simulation results show that the variable compensation networks can obtain high transfer efficiency of the BI-UWPT system.

Frequency selection for underwater wireless power transfer based on the analysis of eddy current loss

Wireless power transfer (WPT) technology is ideal for wireless charging of unmanned underwater vehicles (UUV). However, in underwater WPT systems, the eddy current loss (ECL) caused by the conductivity of seawater cannot be ignored. This paper obtains the expressions of the equivalent ECL resistance and mutual inductance by calculating the complex power generated by the current in the electric field. An intuitive circuit model is used to describe ECL and its superposition effect. Based on the system efficiency expressions, the influence of the medium conductivity, coil gap and operating frequency on the transmission efficiency is analyzed. Results show that there is an optimal frequency to achieve the maximum dc–dc efficiency in the seawater. Simulated and experimental results verify the validity of the method in calculating ECL and capturing the optimal transmission frequency.

A review of underwater inductive wireless power transfer system

AbstractThe IPT system has been studied for underwater applications such as autonomous underwater vehicles (AUVs) and subsea sensors. However, it rarely comparatively shows the performance of the IPT system in air, freshwater, and seawater. Based on the fore‐mentioned research background, this paper presents a survey of the properties of the IPT system in different mediums. Here, a 100 W power‐level experimental IPT prototype is built and tested. The resonant frequency is set at 300 kHz with a gap range from 10 to 190 mm. The comparison is focused on the efficiency, mutual inductance, coupling coefficient, coil resistance, and quality factor of the IPT system. The IPT system is placed in air, freshwater, and seawater with the same settings. What's more, the magnetic fields of coupling coils in air, freshwater, and seawater are presented in this paper. This paper could be acted as a reference to optimize the IPT system and facilitate future IPT research for underwater applications by analysing the performance of the IPT system in different mediums. The 3D Ansys Maxwell simulation of the IPT system is also given here to study the magnetic fields.

Experimental results and analysis of midrange underwater wireless power transfer

SummaryIt is reported generally in previous studies that the transmission efficiency of wireless power transfer (WPT) system in seawater is lower than that in air due to eddy current loss. In this study, it is found experimentally that the transfer efficiency in seawater can reach 17 times of that in air on average at midrange for a WPT system with two 22.5‐cm planar coils and a 460‐kHz resonance frequency. These show that the eddy current assists wireless transfer in seawater, and then the eddy current is treated as a relay coil to explain the experimental observations. Compared with the model from electromagnetic field theory, which is complex and difficult to grasp, the circuit model proposed in this study is concise and easy to understand. Though the underwater WPT system has a relatively low average transfer efficiency of 20% at midrange, it can be used in a transfer distance priority scene.

An Underwater Simultaneous Wireless Power and Data Transfer System for AUV With High-Rate Full-Duplex Communication

This article proposed an underwater simultaneous wireless power transfer and data transfer system for the autonomous underwater vehicle. The double-sided <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLCC</i> compensation topology is proposed to effectively suppress the interference to the data channel at switching instant. With the increase of the size and turns of the coupling coils, the self-resonance frequency gradually decreases. However, the frequency of data carriers is usually much lower than the self-resonant frequency, which will reduce the data rate or improve the bit error rate at a high data rate. Moreover, the high voltage generated by coupling coils causes high voltage stress on the data channel. To deal with these two issues, the last turn of each coupling coil is used to transfer data in the proposed system. The two transceivers are, respectively, connected with the last turn of the two coupling coils, which excites the entire coils to self-resonate and generates two resonant frequencies. The two resonant frequencies are utilized to realize high-speed full-duplex communication. And the voltage stress of the data channel is effectively reduced. A 518-W full-duplex prototype is built, and the maximum data rate is 700 kb/s, which verifies the feasibility of the proposed system.

Adaptive Wireless Power for Subsea Vehicles

Abstract Wireless power transfer in seawater removes the inherent risks and complexities of mating conductive surfaces in seawater. An effective underwater wireless power transfer system for subsea vehicles must maintain power transfer despite the potential for dynamic misalignment between the power transmission and receive elements and therefore requires an adaptive system. We describe the development and characterization of a subsea wireless power system, including a transmit-receive coil pair optimized for seawater performance. Built on the adaptive resonant wireless power transfer technology of WiBotic, Inc., the system automatically adjusts for misalignment and separation between the transmit and receive coils. We demonstrate that transmit-receive coil pairs can be effectively tuned to provide adaptive wireless power transfer in salt water, with no significant effects of increased pressure at depth. Furthermore, we describe the full system marinization of the wireless power system and its application to a system that uses a wave energy converter for subsea vehicle charging.

Enabling Underwater Wireless Power Transfer towards Sixth Generation (6G) Wireless Networks: Opportunities, Recent Advances, and Technical Challenges

In recent decades, wireless power transfer (WPT) has gained significant interest from both academic and industrial experts. It possesses natural electrical isolation between transmitter and receiver components, ensuring a secure charging mechanism in an underwater scenario. This ground-breaking technology has also enabled power transmission in the deep-sea environment. However, the stochastic nature of the ocean highly influences underwater wireless power transmission and transfer efficiency is not up to that of terrestrial WPT systems. Recently, the research fraternity has focused on WPT in the air medium, while underwater wireless power transfer (UWPT) is challenging and yet to be explored. The major concerns are ocean current disturbance, bio-fouling, extreme pressure and temperature, seawater conductivity and attenuation. Thus, it is essential to address these challenges, which cause a substantial energy loss in UWPT. This study presents a comparison between various WPT techniques and highlights the research contributions in UWPT in recent years. Research and engineering challenges, practical considerations, and applications are analyzed in this review. We have also addressed influencing factors such as coil orientation, coil misalignment and seawater effects in order to realize an efficient and flexible UWPT system. In addition, this study proposes multiple-input and multiple-output (MIMO) wireless power transmission, which can significantly improve the endurance of autonomous underwater vehicles (AUVS). This idea can be applied to the design of an underwater wireless power station for self-charging of AUVs.

Experimental Investigation of Transfer Characteristics of Midrange Underwater Wireless Power Transfer

The transfer characteristics of an underwater Wireless Power Transfer (WPT) system with a resonant frequency of 460kHz are studied experimentally. The coils have an outer diameter of 22.5 cm. Through this study, it was found that when the transfer distance is small, the transmission effect of WPT system in seawater is similar to that in air; when the transfer distance is larger than 20 cm, the load voltage of the WPT system in seawater is 4 times higher than that in air, and the transmission efficiency in seawater can reach 17 times of that in air on average. The experimental results in this paper are compared with studies published, and a circuit model is proposed to explain and predict the experimental phenomena, but the specific model still needs further work. Finally, the underwater WPT system has a low transfer efficiency of only 20% at midrange, so the findings of this research may be used for distance first scenarios.

Review of low‐loss wireless power transfer methods for autonomous underwater vehicles

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.

Comparison Survey of Effects of Hull on AUVs for Underwater Capacitive Wireless Power Transfer System and Underwater Inductive Wireless Power Transfer System

Underwater wireless power transfer (UWPT) system has attracted widespread attention. It has been used for power delivery for underwater equipment in the marine environment with high safety and convenience. However, the material of metal plates and the shape which will affect the high frequency alternating electromagnetic fields and the high frequency alternating electric fields for the inductive wireless power transfer (IPT) system and the capacitive wireless power transfer (CPT) system. This paper presents the effects of the hull of the autonomous underwater vehicle (AUV) on the underwater wireless power transfer system including the underwater capacitive wireless power transfer (UCWPT) system and underwater inductive wireless power transfer (UIWPT) system. The features of underwater wireless power transfer systems have been carefully studied with simulation and experimental work. The experimental water tank has been constructed with the 35‰ salinity water. The hull of AUVs has been respectively simulated and built with rectangle metal plates and curved metal plates. The original experimental data and phenomenon have been presented in this paper. The different performance of the UCWPT system and UIWPT system is provided and discussed in this paper. The comparison work with the related paper has been analyzed. This paper could be acted as the reference for designing the underwater wireless power transfer system for AUVs.