This study introduces an power-boosted wireless power transfer (PBWPT) system by concurrently utilizing both the 1stand 3rdharmonics of the square voltage generated from the inverter. The key is to integrate a bipolar coil inside the unipolar coil to establish two decoupled power transfer channels in the same space. Specifically, both sides adopt symmetric coil structures while the unipolar and bipolar coils resonant at the 1st and 3rd harmonics, respectively. Under the same input DC voltage and transfer distance, compared with the traditional fundamental-harmonic single-channel WPT system, this approach can improve the average output power by 66.03% and the average system efficiency by 12.43% in the load range of 1-100Ω, respectively. Finally, the theoretical analysis and simulation results are given to validate the effectiveness of the proposed PBWPT system.

Inductive power transfer (IPT) systems conventionally operate at the natural resonant frequency for efficient power transmission, but their output power is sensitive to mutual inductance changes. Recent studies have shown that parity-time-symmetric IPT systems have two splitting frequencies in the strongly coupled range, enabling robust wireless power transfer with constant output power and high efficiency. Self-excited oscillation circuits can automatically track these optimal frequencies without measuring circuit parameters. However, practical self-oscillating systems contain voltage harmonics and feedback delays, which are often ignored in the analysis of steady-state performance. In this paper, the effects of high-order harmonics and time delay on steady-state frequencies are systematically analyzed. First, the formula of ideal bifurcation frequency is derived based on the zero-phase-angle condition. Then, steady-state conditions under square wave voltage and feedback delays are obtained using the Fourier series and superposition theorem. Finally, numerical examples demonstrate that exceptional points shift towards stronger coupling due to harmonics, whereas time delay could eliminate frequency bifurcation.

In this paper, a robust closed-loop speed control for wireless motor systems is proposed with the consideration of maximum efficiency point tracking (MEPT). Firstly, the optimal load condition for maximum efficiency point tracking of wireless motor systems is derived, a buck converter with an optimal duty cycle is adopted to achieve impedance match of the wireless power transfer system such that maximum efficiency can be guaranteed. Then, an integral fixed-time sliding mode (FTSM) control strategy is designed to achieve robust speed tracking control for wireless motors in the presence of parameter variation and external disturbance. The simulation results illustrated superior tracking performance with 15.90% speed tracking overshoot reduction, 26.90% speed tracking error RMS reduction compared with the conventional PID control. And the efficiency of the WPT systems is well maintained at 85.55% simultaneously.

In a wireless power transfer (WPT) system, maximum efficiency can be achieved at specific load conditions by employing impedance matching (IM). Some researchers employ DC-DC converters or additional inductors and capacitors; however, this inevitably leads to an increase in both system cost and complexity. In this paper, we propose a receiver-side variable capacitor system, which comprises a series-connected switch-controlled capacitor (SCC) and a parallel-connected relay-controlled capacitor (RCC). This system aims to achieve maximum efficiency tracking (MET) for WPT across a wide range of load variations. The proposed system autonomously detects variations in the load and adjusts the equivalent capacitor value to achieve MET. Experimental results demonstrate that the proposed system can enhance system efficiency by approximately 5% to 20% when the load varies from 60 Ω to 180 Ω. Finally, we validate the feasibility of the proposed system through experimental verification.