Abstracts:To address the issues of limited output power and harmonic interference in existing multifrequency and multiload magnetic coupling resonant wireless power transfer (MFML-MCR-WPT) systems, this article proposes a MFML-MCR-WPT system based on a cascaded H-bridge multilevel inverter (CHB-MLI). The system utilizes the phase disposition multifrequency modulation technique, achieving arbitrary frequency and quantity power output and control through the design of modulation wave quantity, frequency, and amplitude. First, the structure of the CHB-MLI-based MFML-MCR-WPT system is proposed, and the working principle of the multifrequency modulation method is analyzed. Subsequently, a five-level dual-frequency and dual-load system is taken as an example to establish the mathematical model. Then, system parameter optimization is conducted to suppress cross-coupling and interfrequency interference. Furthermore, to address the power and loss imbalance among H-bridge units under multifrequency low modulation indices, a carrier reconstruction method is adopted to balance power distribution and switching losses. Finally, an experimental platform is constructed to validate the proposed theory. Simulation and experimental results demonstrate that the system achieves multilevel multifrequency power output with continuous power and frequency control, maintains minimal interchannel interference, and achieves H-bridge unit balancing ratios of 1:1.19, while exhibiting excellent system compatibility and controllability.

Abstracts:Currently, coil misalignment is recognized as one of the primary factors limiting the transmission efficiency of wireless power transfer (WPT) systems, presenting a substantial barrier to the large-scale adoption of WPT. To enhance transmission efficiency under misalignment, mitigate the impacts of misalignment, and increased transmission distance of WPT systems, research on Hilbert fractal curves in related fields was referenced, mutual inductance expressions for coils with Hilbert-extended structures and conventional coils were derived based on their mathematical formulations, and the potential advantages of Hilbert curves in wireless power transfer applications were analyzed. Supported by extensive simulation outcomes, a fractal coil incorporating a Hilbert structure was designed without altering coil manufacturing costs. The transmission performance advantages of this coil were investigated through simulations. A WPT system verification platform utilizing an LCC-S circuit was constructed, where 300 W power and efficiency tests were conducted under relatively consistent zero voltage switch (ZVS) conditions for both coil types. Experimental results across varying transmission distances and misalignment distances were obtained. The results demonstrate that the proposed coils comprehensively optimize the power transfer capability of conventional coils, delivering more stable output power and improving the transmission efficiency by over 10% (up to 24%).

Abstracts:Parameter identification-based control strategies are considered the preferred solution for achieving constant current (CC) and constant voltage (CV) charging control in communication-free inductive power transfer systems. However, identification errors in mutual inductance, load resistance, and other parameters can affect control accuracy. To improve control accuracy and response speed, a communication-free control strategy based on neural networks and deep transfer learning is proposed. This strategy eliminates the need to identify parameters like mutual inductance and load resistance. Only a few measured datasets are required to train the network model offline, and a trained model can online estimate output voltage/current. By combining with a controller, CV/CC charging control can be achieved under conditions of real-time variations in mutual inductance and load resistance. The experimental results show that the proposed control strategy achieves a static error of only 1.5% and a response time of no more than 24 ms. Compared to the parameter identification-based control strategy, the proposed strategy demonstrates lower static error, shorter response time, and a wider dynamic range.

Abstracts:Synchronized switch interface circuits demonstrate good performance for electromagnetic energy harvesting applications, but lack adaptability in terms of harvested power. This article introduces an additional control degree of freedom by proposing two power control methods and implementing them in a synchronous current inversion and energy extraction (SCIEE) circuit. Theoretical analysis indicates that the single-stage system achieves higher efficiency for approximately 41.3% of the supported load range compared to using a commercial dc–dc regulator. In the load transient experiments, the proposed system maintains the output voltage well-regulated, with undershoot and overshoot below 0.2 V. The output voltage ripple is 0.15 V at an 18 mA load current. The proposed system is compared to three other options: a direct ac–dc harvesting circuit, the synchronous switch energy extraction (SSEE) circuit, and a two-stage harvesting system using a commercial dc–dc regulator and an open-loop SCIEE circuit. The proposed system supports a maximum load current of 29.47 mA, the highest among these options. In a field test, the proposed system supports successful integrated circuit long range (LoRa) packet transmissions and exhibits a broader supported load range than the SSEE or direct ac–dc harvest scheme.

Abstracts:Misalignment tolerance represents a critical challenge in uncrewed aerial vehicle wireless power transfer (UAV-WPT) systems. Conventional approaches enhance positional and angular misalignment tolerance by generating wide-range omnidirectional magnetic fields through transmitter design or rotating field techniques. However, these methods exhibit a low magnetic field utilization rate since UAVs typically require only specific field orientations postlanding rather than omnidirectional fields. This article proposes a UAV-WPT system employing two orthogonal bipolar transmitting coils with a targeting magnetic field to achieve omnidirectional powering and enhance the magnetic field utilization rate simultaneously. COMSOL simulations are used to analyze the magnetic field distribution of the transmitter, and the principles for generating a targeting magnetic field through excitation current control are explained. The amplitude and phase of the excitation currents are controlled by adjusting the duty cycle and phase difference of the two half-bridge inverters. The mathematical relationships between maximum output power, maximum input power, and maximum transmission efficiency with respect to duty cycle and phase difference are established. A targeting magnetic field control method combining phase difference and duty cycle scanning is proposed. Experimental results show that the system can establish a targeting magnetic field within 85 ms, with a maximum output power of 216.2 W and a peak dc-to-dc efficiency of 89.5%. The dc-to-dc efficiency exceeds 76.1% across ±100 mm positional misalignment and arbitrary angular misalignment. The dc-to-dc efficiency of the targeting magnetic field mode is at least 5% higher than that of the rotating magnetic field mode.

Abstracts:The elliptical ultrasonic tool holder (EUTH) is a critical core component in elliptical ultrasonic vibration-assisted milling. Traditional EUTH employ conductive slip rings for power transmission, which severely restricts milling speed. This study investigates an efficient noncontact power transfer method for EUTH, utilizing a dual-channel rotary transformer to replace conductive slip rings. Electrical energy is transferred through air coupling between the primary and secondary sides of the rotary transformer, and this frictionless power transmission method eliminates limitations on milling speed. A finite element model of the elliptical ultrasonic transducer was used to analyze its modal shape, impedance, and resonant frequency temperature drift characteristics, thereby determining the transducer's resonant frequency, vibration amplitude, and node positions. The rotary transformer was designed using ferrite core material with high magnetic permeability and low electrical conductivity to reduce eddy current losses. An equivalent circuit model of the EUTH was established, and compensation circuits were designed to improve the efficiency of noncontact power transfer. A dual-channel ultrasonic generator (DCUG) was developed using a Class D amplifier, enabling adjustable voltage amplitude, phase, and frequency. A Fuzzy-PID algorithm was implemented to achieve automatic resonant frequency tracking for the DCUG. Finally, a milling platform was set up to conduct elliptical ultrasonic vibration-assisted milling experiments, where the DCUG drove the EUTH. Experimental results show that below 40 kHz, the maximum driving voltage of the dual-channel ultrasonic generator reaches 300 Vp-p, while the elliptical vibration displacements at the tool tip in the X- and Y-directions are both approximately 20 μmp-p. The output amplitude current remains stable, and the system automatically tracks the resonant frequency of the EUTH during milling. This provides an effective method for achieving high-efficiency noncontact power transfer in EUTH.

Abstracts:Wireless power transfer (WPT) systems with battery loads exhibit low damping, which results in significant current overshoots and sustained oscillations when subjected to disturbances. Pulse skipping control is frequently employed in WPT systems and can be considered a significant disturbance. However, the accurate analysis of the resulting system dynamics and current envelope remains a challenge. To allow accurate evaluation of the performance of WPT systems with pulse skipping, this article introduces a new reduced-order model for WPT systems through balanced truncation. The derived second-order model enables real-time computation of the current envelopes on both sides of the system, facilitating a comprehensive analysis of the overall performance. This article presents two case studies that utilize this reduced-order model to optimize pulse skipping control in WPT systems. The first study proposes a pulse skipping soft-start strategy based on this model. The second study investigates the optimal pattern of pulse skipping modulations. Simulations and experimental results from a laboratory prototype validate the effectiveness and feasibility of the proposed reduced-order model and the design and refinement of the pulse skipping patterns.

Abstracts:To reduce the volume of the secondary side of an electric vehicle wireless power transfer system, integrated LCC compensation has become a prevalent approach. However, integrated inductors introduce additional coupling effects among the integrated inductors and the power coils, which may influence the input impedance angle, and increase electrical stresses. To circumvent this problem, this article proposes a nonpolar method for integrated compensation inductor design. The main idea behind the proposed method is to first separate a single compensation inductor into two bipolar inductors, then reconfigure the wirings so that the currents flow in opposite directions, which helps to mitigate their cross interactions. Since this approach decouples the compensation inductors from the power coils, the system becomes more compact and, at the same time, the symmetrical layout results in lower coil current stresses and reduced electromagnetic interference. The universal harmonic-considered time-domain model for vehicle-side magnetic integration is deduced. Furthermore, a systematic comparison of soft-switching behavior between conventional integrated solutions and the proposed topology is carried out under varying misalignment conditions. Experimental results obtained from a 11-kW prototype show that the proposed system achieves zero-voltage switching over the specified misalignment range, with a peak efficiency of 93.4%. A video showing the waveforms of the system during the misalignment process is provided in the Supplementary Material.

Abstracts:The switched mode power amplifier (PA) is widely used for high frequency high power applications due to its high efficiency. In the switched mode PAs, impedance matching network (IMN) is usually needed to ensure that the varying load impedances can be matched to the target impedances for high efficiency. The existing IMN design methods usually depend on empirical trial and error, load pull simulation, and numerical optimization, which cannot achieve actual region-to-region impedance matching. Therefore, this article proposed a novel impedance matching design approach for switch mode PAs based on the property of circle preservation in Möbius transformation which guarantee that all the impedance points in a region or trajectory can be precisely transferred to the target region or trajectory. The proposed approach gives the simple and explicit formulas to design the IMN parameters, which helps solve the design challenge of accurate impedance matching for large load region. And the impedance matching design for frequency tuning control is also presented to achieve high efficiency and multilevel power modulation over a large impedance region. For verification, a 500 W 13.56 MHz GaN-based class E PA is built and the experiments show that the PA with proposed matching design can achieve 87.2%–95% efficiency over a large load region. And the high speed pulsing (200 kHz) and multilevel (25.6 kHz) power modulation can be also achieved by frequency tuning with ultra-fast transitions (369 ns) and 91% average efficiency by using the proposed design.