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Long-range underwater wireless power transfer (WPT) systems have great application prospects in many industrial fields. However, conventional WPT systems may suffer different kinds of technical issues in this highly unstable operation environment, such as large output decay when the transmission distance increases, and output fluctuation caused by instability of the water flows. To solve these problems, this article proposes a novel solution to achieve an enlarged resonance range, higher efficiency, and more stable output. The LCC-S-S compensation circuit is adopted in the system with a highly stable primary current, which improves its fault tolerance ability to adapt to the unstable underwater environment. A portable omnidirectional magnetic resonant extender is designed as an intermediate device to extend the underwater transmission distance and raise the system’s efficiency. The specially designed structure enables it with two separate but complementary three-coil WPT systems which solves the conventional angular dead zones issue. Theoretical analysis proves that under the idealized conditions, both the magnitude and phase of the load current can be effectively maintained as absolute constant, with arbitrary water flow direction or velocity. Both circuit simulation and finite element analysis (FEA) results are presented to validate that the system is possessed with high fault tolerance. For further assessment, an experimental prototype is established, and the practical test results confirm that the system can maintain a relatively high transmission efficiency under large lateral and angular misalignments ranging from −90° to +90°.

High-frequency power converters are gaining increasing attention and popularity due to the high power density and high efficiency demand in electric vehicles (EVs). In this condition, high-frequency current sensing accuracy is essential. However, existing current sensing methods cannot meet the needs in terms of low power loss, small size, being contactless, or large bandwidth. This article proposes a new current sensing technique with bandwidth enhancement. First, a skin effect model for commonly used rectangular conductors is investigated. Then, variations of out-of-plane and in-plane magnetic fields caused by skin effects are analyzed theoretically. It reveals that measuring out-of-plane magnetic fields shows a larger bandwidth than measuring in-plane magnetic fields. Subsequently, a circle trace for current sensing is proposed. The corresponding simulation results illustrate necessary considerations in a circle trace-based printed circuit board (PCB) design. Then, the current responses of a proposed circle trace and a conventional straight trace are compared in experiments. In experiments, the step current response has an average improvement of 48%, and the measurement bandwidth is extended from 10 to 200 kHz using the circle trace method. These experimental results confirm that the circle trace shows better performances. Thus, the proposed method is validated for application in high-frequency current sensing.

This article proposes and implements a wireless hybrid stepper motor (HSM) system, which offers high controllability of speed, direction, and position without physical contact and electrical connection between the power source and the motor. By transmitting electrical pulses to each motor winding in different frequencies, duty ratios, and sequences, the speed can be regulated to expected values, and the rotation angle of each step and direction can be controlled without any sensors or controllers at the secondary side. Two orthogonal bipolar coils and double-frequency resonant networks are adopted to provide four decoupled current channels to control the four self-drive switches independently at the secondary side. Thus, various operating modes can be realized for different working requirements. To equalize the power output at all phases, pulse frequency modulation is adopted to maintain robust zero-voltage switching. The motor can carry a 1.5-N·m load at the speed of 430 rpm and provides speed and position control capability. The theoretical analysis, computer simulations, and hardware experimentations are given to verify the feasibility of the proposed wireless HSM system.

High-temperature superconducting tapes can be stacked together to form cables which are then wound into coils for potential use in electrical machines. The tapes in the cable can either be uncoupled (insulated from each other), coupled at ends (coupled at the terminals of the cable), or fully coupled (electrically connected with each other along the whole length of the cable). The integral method can readily model the uncoupled scenario, and this article extends the integral method to model the coupled-at-ends and fully coupled scenarios. We find that the proposed method has a time advantage over the well-established T–A formulation of Maxwell's equations.