Modular parallel multi-inverters (MPMIs) with master-slave phase synchronization control is proposed for high-power wireless power transfer (WPT) where the MPMI output voltage phase is synchronized to suppress current circulation by compensating for the time delay of the slave inverters caused by signal propagation delay. Different power levels can be conveniently satisfied by flexibly adjusting the number of MPMIs. A modeling method based on the energy-amplitude and phase is developed and linearized to get the slowly changing phase variable and to analyze the system dynamic characteristics at its operating point. To achieve the required dynamic performance of the proposed model, the parameters of a PI controller are obtained by calculating the required settling time and overshoot of the closed-loop dominant poles. A 20.07 kW WPT prototype supplied by three MPMIs with an efficiency of 92.17% was designed and tested. Experimental results show that the proposed modeling method and controller design achieved both good performances of circulating current suppression and MPMIs output voltage phase synchronization.

In this brief, a novel wireless individual-drive system for variable-reluctance(VR) stepping motor is proposed and implemented. The key is to use coil groups to drive each phase of the VR stepping motor individually through magnetic resonance coupling. Based on the proposed structure, the VR stepping motor can be driven wirelessly while the motor side is free of active components. Meanwhile, the constant current drive is achieved without a chopper. The proposed system enables the VR stepping motor to work with higher independence and robustness compared with the cable-powered motor. The system design is described at first. Then, the equivalent circuit model is derived and analysed. In addition, the operation principle is displayed. Finally, a system prototype is constructed in the laboratory to validate the effectiveness of the proposed system. The experimental results show that 87.5% efficiency from dc power source to motor winding is achieved with the transmission distance of 50 mm. Moreover, the motor speed can reach up to 150 r/min and the motor torque can be regulated with the duty-ratio modulation.

Wireless power transfer system (WPT) is an interesting alternative for charging electric vehicles and has a broad prospect in public transport applications. In order to obtain optimal power transfer, the existing WPT systems often require perfect alignment between the primary and secondary coils, which can hardly be met in real applications. To relieve this problem and achieve the goal of free positioning, a one-to-multiple WPT topology being able to improve the misalignment tolerance at secondary side is proposed in this letter. Based on circuit analysis and Matlab simulation, a mixed mode is proposed to obtain a steady power transfer with horizontal misalignment. To verify the proposed topology, a one-to-two WPT system with a three winding transformer is developed in this letter, showing that proposed topology with the mixed mode can significantly increase the positioning adaptability.

Wireless charging has become increasingly popular for electric vehicles (EVs) in recent years. However, possible device damage may happen because of the sharp variations of inverter output current and ZVS angle due to the alignment variation between resonant coils especially while charging. To design a protection strategy, the characters of inverter output current and phase angle are analyzed when the wireless charging EV leaves. The protection strategy is composed of the insufficient angle protection, overcurrent protection, and the excessive angle protection. A detection circuit is designed to measure the variation of inverter output current and phase angle. A wireless charging EV prototype is established to validate the proposed methods. The experimental results show that the designed detection circuit and protection strategy can catch the abnormal working state of the system when the wireless charged EV leaves and take measures immediately to protect the main circuit of the system from device damages.

In this paper, a parallel modular multi-inverter (PMMI) topology is proposed to supply high power for wireless charging electric vehicles (EVs). A major challenge in the implementation of PMMI topology is zero-voltage switching (ZVS) for all inverters to avoid high-frequency switching losses. Therefore, a centralized-ZVS control and master–slave frequency following (MSFF) strategy are presented to realize ZVS for all PMMIs by a single controller structure without extra controllers needed on the slave inverters. Meanwhile, a modeling method directly related to the ZVS angle and operating frequency for an arbitrary number of PMMIs is proposed and linearized to analyze the system dynamic characteristics at the operating point. Additionally, to obtain the desired dynamic performance, an optimal controller coefficient (OCC) configuration method is proposed for the design of controller parameters. Finally, a laboratory wireless power transfer (WPT) prototype supplied by three PMMIs is designed, built, and tested to verify the correctness of the theoretical analysis. Experimental results show that the ZVS angle of all PMMIs can maintain at the preset value with the desired settling time under designed the PI controller parameters. The measured whole system power transmission efficiency is $94.1\%$ at a 10 $\mathsf{\Omega }$ load.