Peng Zhao

In series–series compensated bidirectional inductive power transfer systems, the resonant currents are cross coupled due to the influence of multiresonant elements. This makes it difficult to analyze the system behavior using conventional state-plane analysis (SPA) method. To address this challenge, a novel decoupled SPA approach is proposed. It establishes two decoupled equivalent circuits and corresponding state-plane trajectories by decoupling the coupling coil model. Thus, resonant voltages and currents in switching instants can be derived. In addition, the zero-voltage-switching (ZVS) range with different phase shifts and frequency ratios can be determined, and the rms currents of coils can be analyzed quantitatively. To validate the proposed model, a 400-W-rated laboratory prototype is designed and tested. The experimental results align well with the theoretical predictions, and confirm the ZVS among all mosfet s. The proposed method is universal and can be used to analyze other compensation networks.

This letter proposes an inductive power transfer system to maintain stable output power in an ultrawide coupling variation range. Taking the series–series compensation as an example, the theoretical limit of detuned compensation is studied by defining two general impedance factors. Based on the circuit transformation, various detuned compensations can be studied in a unified manner, and then used to explain the mechanism of the proposed LCC/S-S system. The soft-switching consideration is incorporated in the design of proper factors. When a real system adopts the proposed compensation, it would naturally ensure 20% power fluctuation (from 130 to 163 W) in an ultrawide coupling coefficient range (from 0.07 to 0.33), and maintain the efficiency above 80%.

Due to the compatibility considerations, it is not attractive for the commercial wireless charger to modify the Qi-standard coils for charging multiple loads. This paper would explore the potential of a power relay module (PX) to address this issue. The multiple-coil PX would enhance the effective coupling when the standard coupler fails. In this paper, different types of PXs are developed for various applications, including a two-coil PX using series compensation, a two-coil PX using high-order compensation, and a three-coil PX using high-order compensation. Their power and efficiency characteristics are analyzed in a uniform manner, and the benefits of different PXs are justified through a planar charger and a bowl-shape charger in the experiment. The implemented bowl-shape charger is able to offer one fast-charging channel for a single device (30 W) and one multiple-load channel for at most four devices (each 10 W) simultaneously. The peak efficiency is 88% when the overall delivered power of PX is 70W.

This paper proposes a five-coil bowl-shape wireless charger based on a H5 bridge inverter. Inside the bowl, the five coils are customized and placed at different charging areas, which are able to offer two power channels for fast charging and multi-load charging respectively. A five-switch H5 bridge inverter is used to feed the optimal voltage through its multi-mode operation, which helps enhance the efficiency under various load conditions. The zero voltage switching is discussed for all the switches and achieved under the worst case, which is justified by the harmonic analysis. Finally, a 50-W experimental prototype is built and measured under various load conditions, and the peak charging efficiency is 88%.

An inductive power transfer system is able to charge multiple receivers (RXs) through a single transmitter. In order to develop suitable control methods, this article explores and compares the influence of driving current and loading resistance on the efficiency and power distribution. It starts from a simple system with equal coupling and then extends the discussion to a general one. With proper simplification, an optimization problem is defined to derive several important factors, including the optimal driving current, optimal loading resistance, and the corresponding optimized efficiency under various application constraints. In the final experiments, the dynamic tuning of driving current is able to maximize the system efficiency to 92.1% for a general three-RX system. In another customized system with equal coupling, the maximum error between the achieved efficiency and the real maximum efficiency is 0.4% through the calculation-based current control.

The LCC–LCC compensation is widely used in the inductive power transfer systems. However, there is no simple and accurate small-signal equivalent circuit model for this resonant converter. Based on the extended describing function method, this article proposed a full-order (17th-order) equivalent circuit model to accurately predict the small-signal behaviors. For simplification, the full-order model is gradually simplified to a ninth-order model and finally to a fifth-order model. The input to output transfer function are analytically derived for the first time. Both simulation and experimental results are presented to justify the effectiveness of the model, and the model is accurate up to one-fifth of the switching frequency.

This article explores the potential of relay coils (ReXs) to extend the horizontal charging area for planar inductive couplers. It focuses on the coupling mechanism and derives the equivalent coupling coefficient for model simplification. Based on the new model, a one-ReX coupler is proposed to enhance the coupling under large misalignment. Besides, the influence of coupling polarity change is evaluated and well compensated. In order to further enhance the coupling, a multiple-ReX technique is proposed and justified by a two-ReX coupler and a three-ReX coupler. The experimental result shows that the enhanced coupling coefficient helps maintain the efficiency to be above 92.5% under large misalignment when the one-ReX coupler is used. With three ReXs, the achieved efficiency is further improved by 2.3%.

Most of the existing wireless offline chargers would employ redundant power conversion and isolation stages to charge a low-voltage battery, which leads to limited overall efficiency. In order to address the redundancy issue, this article proposes a wireless fast charger by using a two-stage configuration. An unregulated inductive power transfer (IPT) stage can not only offer galvanic isolation, but also provide high step-down voltage ratio, and then, only a simple buck converter is needed for voltage regulation. This article evaluates the influence of voltage gain on efficiency and voltage stress of an LCC-C compensated IPT stage. The zero-voltage-switching (ZVS) lost mechanism is also studied and evaluated by a proposed ZVS model. Finally, a 45-W fast charger prototype is designed for 264-V/12-V conversion. The measured peak efficiency is 78%, which is much higher than the Qi-based charger.

This article proposes a parametric fault detection method for switching power converters. The method generates a health indicator to represent the health condition of the entire power converter, and parametric faults are detected with any abnormality of the health indicator. The method first introduces a systematic mathematical modeling framework to describe all the physical laws of the switching power converter during healthy conditions. Afterwards, the dynamic state estimation via batch mode regression is applied to solve the states of the system and to generate the health indicator. The health indicator sensitively reflects the consistency between the actual measurement and the healthy circuit model by taking the statistic characteristics of solution into consideration. The proposed method only requires terminal measurements of the switching power converter, and does not have further assumptions on the topology of the converter. Compared to the existing observer based approaches, the method presents higher sensitivity during parametric faults. Compared to the existing parameter identification based approaches, the method does not need to estimate all the parameters of the converter in order to detect parametric faults. Simulation and experimental results on an example buck converter prove the validity of the proposed parametric fault detection method.