The lightweight design of the receiver plays a pivotal role in the application of wireless power transfer (WPT) technology to intelligent devices, such as unmanned underwater vehicle (UUV) and autonomous aerial vehicles (UAVs). This article utilizes frequency-variable auto-resonance technology to tackle the problems of weak antideviation capability and non monotonic control curve encountered in lightweight design of traditional series-series (SS) topology. Additionally, since this technology can maintain constant efficiency under the desired power, antideviation control can be achieved through frequency regulation solely based on input voltage and current information, eliminating the need for wireless communication. The experimental prototypes demonstrate that this study can achieve 100-W constant power transmission with a 5- $\mu $ H receiving coil, weighing only 4 g and achieving an efficiency of 90.7% under load and position variable conditions.

For the fully resonant wireless power transfer (WPT) system, the high coupling of the converter and the resonant network introduced many problems, such as frequency splitting, the power curve peak limit, and the strict switch strategy. To solve these problems, this paper proposed a new six-switch topology based on the full–-bridge converter. With the unique structures containing two capacitor-isolated switches and a source-isolated diode, the system decouples the converter and the resonant network, and its modes have been decoupled, called the independent power injection and free resonance WPT (IPIFR–WPT) system. The capacitor-isolated switches and the source-isolated diode make the converter operate only when the voltage on the primary capacitor is equal to the source voltage, and the source will be isolated by the diode when the capacitor voltage is great than the source, which provides a wide time margin for the switches of the converter to turn on in advance. In this margin, the operation point is self-determined the same whenever the switches turn on so that the system’s performance is consistent. Based on this characteristic, the system can self-adapt a dynamic change in system parameters, with at least 15% tolerance for the coupling coefficient and 14% for the load resistance.

In wireless power transfer system, the frequency splitting phenomenon occurs due to over-coupling and low impedance loads, which lead to reduced transmission power. This letter proposes a method using series-connected variable inductors (VIs) on both primary and secondary sides to avoid frequency splitting under fixed frequency condition, while zero voltage switching and zero current switching can be realized over a wide range Lastly, a 100W experimental prototype was constructed, and results indicate that at a fixed input voltage of 50V, the system achieves an efficiency of 87.3%. In comparison to the condition of FSP, the input power shows a 336% improvement, rising from 22.9W to 99.3W.

The coupling of converters with resonant networks poses significant challenges for frequency tracking and power control in inductive power transfer (IPT) systems. This paper presents an implementation method that addresses these issues by dividing the system’s operation into two distinct states: self-oscillating and power-injecting. Based on these states, a phase-closed loop is constructed. Within this closed loop, the phase tracking unit detects and tracks frequency drift, while the power regulating unit incorporates an integrator and adopts a control variable to adjust the output power by modifying the duration of the power injecting state. Meanwhile, the oscillating unit operates in the self-oscillating state. Operating in this manner, the system achieves self-oscillation and demonstrates the capability to effectively track and compensate for system variations within a single cycle. A verification prototype has been constructed, and it demonstrates that the converter within it completely decoupled from the resonant network. Experimental results validate that altering the control variable solely affects the duration of the power-injecting state, allowing for independent control of the output power. When the control variable changes from 2.0 V to 3.5 V, the output power changes from 178 W to 519 W while the self-oscillating state remains unchanged. Furthermore, the system accurately tracks frequency changes, even under significant variations in the coupling coefficient or load, without compromising the power injection state. When the air gap changes from 3 cm to 12 cm, the duration of the self-oscillating state changes from 22.1 μs to 26.3 μs, while the power injecting state remains unchanged. This approach exhibits a robust performance, particularly suitable for dynamic IPT systems sensitive to parameter variations.

Wireless power transfer requires multilevel energy conversion for energy transfer, resulting in a bulky system. This paper proposes a direct AC-AC converter topology denoted as double half-bridge series-matrix converter and introduces a symmetric modulation method that eliminates the need for input voltage polarity detection. The converter circumvents DC conversion and operates at a unit power factor without the assistance of power factor correction. A 1kw prototype was constructed and the same control strategy was adopted, without considering the polarity or magnitude of the input voltage, verifying the accuracy and reliability of the proposed topology. The transmission efficiency was achieved at 91.43%.