Songyan Niu

In this paper, the impact of interlayer parasitic capacitance in dual-layer coils for high-power wireless charging systems is investigated using a 22-kW, 800-VDC example with rectangular, DD, and polyphase pads. Distributed-parameter modeling and finite-element simulations show that the polyphase coil suffers the strongest degradation of effective inductive reactance and quality factor, the DD coil is least affected, and the rectangular coil is intermediate, leading to different efficiency margins and thermal safety risks. The resulting dielectric loss, driven by the combined magnitude of distributed capacitance and voltage stress, is analysed alongside the electromagnetic-thermal trade-offs of spacer materials, particularly regarding dielectric breakdown and thermal conductivity. Furthermore, two winding methods are compared across these coil topologies. The study reveals that the interleaved winding technique, viz., the method II, fundamentally alters the electric field distribution. By counteracting the linear voltage accumulation inherent to standard windings, this method achieves a uniform low-voltage profile for single-phase coils and a suppressed U-shaped profile for polyphase systems, thereby successfully mitigating local hotspots and ensuring reliability.

High brittleness severely restricts the practical use of nanocrystalline cores in low-frequency power electronics. To enhance mechanical strength and facilitate cutting and transportation, curing techniques are commonly employed, yet their influence on the magnetic properties of the cores remains unclear. In this work, three curing techniques, namely, fluid-phase adhesive curing, gel-phase adhesive curing, and vacuum-evacuated gel-phase adhesive curing (VGAC), are applied to prepare cores with varying curing degrees. The magnetic properties of them are quantitatively compared with those of uncured cores within the range of 50–550 Hz. Results show that all three curing techniques demonstrably reduce the eddy current losses of the cores. Specifically, the VGAC-based core exhibits a 50% reduction in eddy current loss compared to the uncured core at 550 Hz and 0.8 T. Meanwhile, high saturation flux density is retained in all cured samples. However, curing also reduces permeability and raises coercivity. Furthermore, cured cores demonstrate increased hysteresis and residual losses, leading to higher total losses. The relationship between core losses and temperature rise is also investigated to provide important guidance for the safe operation of cured cores. In addition, microscopic images under 200× magnification are presented to elucidate the mechanisms underlying these observed influences.

Internet-of-Things (IoT) bolts, which incorporate sensors and are embedded within rail fasteners, are used for monitoring environmental and train status in railway. Wireless power transfer (WPT) is a promising solution for powering these sensors due to its maintenance-free and highly reliable characteristics. However, the large number of bolts makes it costly to adopt the traditional approach where every receiver (Rx) coil is paired with its own transmitter (Tx) coil. To charge multiple Rx coils with a single transmitter, a dynamic-Tx-to-static-Rx (DTSR) WPT approach is proposed. Two key challenges remain. First, conductive and ferromagnetic rails might interfere with the coupling between Tx and Rx coils—a phenomenon that has not been explored previously. Second, due to high-speed trains, charging time is limited to milliseconds. This article is the first to quantify rail interference using a third-order circuit model. On this basis, the challenges and design requirements for DTSR-WPT systems are summarized. Multilayer asymmetrical coils and optimized frequency selection are employed to mitigate rail effects and maximize the energy transferred within a given time. A joule-level WPT prototype with capacitive loads is built. Experimental results indicate that capacitive voltage reaches 80% and 95% of steady-state levels within 6.4 and 9.6 ms, respectively.

This letter proposes an efficient direct-determination method for controller gains and nonlinear friction compensation values of surface-mounted permanent magnet synchronous motor (SPMSM) drive systems, enabling fast deployment and reliable control. First, by leveraging open-loop speed response (SR) characteristics of the high-speed region resulting from sequential signal injection, the inertia-to-flux ratio (i.e., the quotient of total inertia to rotor flux linkage) is directly obtained for gain tuning. Second, with aiding from an equivalent nonlinear friction model, friction compensation values are directly extracted from the natural-decay SR data triggered by zero-value signal injection. Departing from conventional approaches, the proposed method circumvents the need for complex model identification and cumbersome procedures, as well as for laborious internal parameter design. Experiments conducted on a 1.2-kW SPMSM drive system confirm the effectiveness of the proposed method.

Accurate identification of mechanical parameters holds great significance for optimizing control performance and monitoring working status in permanent magnet synchronous motor (PMSM) drives. This work proposes a parameter-tuning-free two-step mechanical parameter identification method using signal injection and algebraic operations. It is devised based on a nonlumped mechanical motion model that incorporates nonlinear and asymmetric friction modeling, which can accurately characterize real-world dynamics. More importantly, the proposed method circumvents the need for parameter adjustments, such as observer gain design and pole placement. With a two-step collaborative mechanism, the developed method is successfully implemented. In the first step, the open-loop speed response triggered by signal injection is exploited to accurately identify nonlinear friction along with the initial inertia value. With aiding from the results of the first step, the second step develops an online algebraic estimator to track the potentially time-varying load torque and inertia. Real-time experiments are conducted on a 1.2-kW practical PMSM drive system to validate the feasibility of the presented method.

Wireless electric vehicle charging (WEVC) is rapidly advancing as an enabling technology for convenient electrified transportation. The trend toward high-power WEVC systems is accelerating, which not only enhances charging speed and user convenience but also introduces new and complex safety challenges. These challenges are particularly acute at the coupler level, where electrical, thermal, and magnetic risks often interact. This review offers a comprehensive analysis of safety management technologies that are specific to WEVC, with an exclusive focus on coupler-related risks. System-level and coupler-level hazards associated with high-power operation are first examined, followed by an in-depth discussion of recent progress in passive safety materials, such as insulation, thermal dissipation, and electromagnetic shielding. Active safety management strategies are also reviewed in detail, including foreign object detection, live body detection, misalignment detection, and multifunctional detection schemes that integrate these capabilities. Emphasis is placed on the ongoing rapid iteration of safety technologies as power levels increase and on the necessity for solutions that are comprehensive, precise, orderly, and reliable. This review concludes by highlighting future research directions, such as data-driven safety management, intelligent sensor integration, regulatory evolution, and user-centered system design, aiming to support the safe and scalable deployment of WEVC in next-generation mobility.

With the growing use of unmanned surface vehicles (USVs) for underwater exploration, efficient wireless charging solutions like inductive power transfer (IPT) are crucial for addressing power limitations. This paper presents a novel IPT system for USVs and introduces a systematic design approach for optimizing magnetic couplers. The proposed design addresses three critical challenges: misalignment tolerance, lightweight construction, and thermal safety, which are intricately linked through a magnetic field. In terms of misalignment, this paper demonstrates that the coil length is a key factor in determining misalignment tolerance. For a lightweight design, replacing the ferrite plate with ferrite bars can significantly reduce the weight of the coupler without causing core saturation. The design is further validated through a two-way coupled electromagnetic–thermal simulation. The results reveal that, with proper thermal management, the system avoids thermal risks in underwater environments compared to air. Finally, a 3 kW prototype is constructed and tested in fresh water, achieving 55 V and 50 A wireless charging at an 85.7% full-load dc-to-dc efficiency, thus confirming the practicality and performance of the design.

Previous studies for calculating the maximum output power (MOP) of wireless power transfer (WPT) systems typically employ fundamental harmonic analysis, which is accurate for loosely coupled WPT systems since high-order harmonics are largely suppressed. However, in practical applications, such as automated guided vehicles, the transfer distance is limited, leading to tight coupling. Inevitably, harmonics are introduced, causing inaccuracies in evaluating the MOP ability and associated operating conditions. In this article, a harmonic model is developed for MOP calculation using a series–series compensated system as an example. On this basis, the critical coupling coefficient is defined to establish the threshold for tightly coupled condition. Under this condition, optimal frequency selection is implemented to improve the output power of system rather than limiting it to operate at the inherent resonant frequency. Furthermore, higher output power is attainable by tuning compensation parameters to enable different resonant states in primary and secondary sides, while ensuring zero-voltage switching. The contribution of high-order harmonics to the total power is quantified. At a transfer distance of 5 mm and coupling coefficient of 0.7, the experimental results validate the accuracy of the harmonic model across a broad load range from 5 to 50 Ω using a 400-W prototype.

As wireless electric vehicle charging (WEVC) technology moves toward commercialization, understanding its associated risks is crucial, particularly with the trend toward high-power fast charging. In this paper, thermal risks and factors exacerbating the risks in wireless EV chargers are investigated comprehensively, focusing on the magnetic coupler and foreign objects (FOs) intruding on the charging area. The power losses and temperatures of the coupler and FOs are obtained using a two-way electromagnetic-thermal coupled model, and the coupler will be assigned to a risk level according to the proposed four-temperature-level risk evaluation mechanism. In this model, practical considerations include coil types, misalignments, FO materials, ambient temperatures, etc. Moreover, a dynamic perspective is used to characterize the trend of risks so as to provide predictive insights. To validate the newly identified risks, two 6.6-kW WEVC prototypes are built employing circular coils and DD coils, respectively. Experimental studies confirm the necessity of implementing thermal risk management strategies for magnetic coupler under misaligned conditions such as enhanced cooling, including a wider range of materials for foreign object detection (FOD), expanding the FOD area, and so forth.