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This paper presents the framework for the applications of double-source wireless systems in charging for movable electronic devices. To acquire the real-time mutual inductances between the receiving coil and the transmitting coils, a detection strategy on the basis of primary parameters (currents and voltages) is introduced, which can replace the wireless communications between the receiving side and the transmitting side. Coordinated control of two source voltages is employed to deal with the power fluctuation of load, which is caused by load position variations. In specific, the constraint of two source voltages, which can maintain the output power stable, is derived. Based on these feasible combinations of source voltages, numerical calculations are further carried out to identify the optimized voltage combination, which can achieve high power transfer efficiency. Finally, an experimental prototype is built up and the results show that the proposed coordinated control strategy can minimize power fluctuation and maintain relative high efficiency at the same time.

The operation of wireless power transfer systems (WPT) with a single relay, which could charge one or multiple receivers simultaneously, is investigated. Besides, a new method for ensuring the optimized transfer efficiency and the output power by configuring the operating frequency is presented, even when the coupling coefficients between all the coils are very small. An issue of concern is that the couplings between receivers cannot be ignored due to limited operating space, which adds to the complexity of both the system design and the control method. The contribution of the research presented here is to propose an optimized strategy which can charge each receiver with identical power and simplify the coupling complexity thereof. Specifically, the efficiencies and outputs of the introduced WPT systems are discussed. In addition, the distribution design according to different numbers of receivers is proposed to guarantee that both the system operating frequency and the output power remain stable. The theoretical analysis is confirmed by both simulation and experimental results.

The monitoring equipment for overhead 110 kV high-voltage power lines plays an important role in the smart grid operations and may be required to work for years without maintenance; therefore, many varieties of energy harvesting devices have been investigated with a variety of problems remained though. In this study, a hybrid wireless power charging proposed system, integrated with magneto-electric and electric-electric conversion, is presented. It consists of an inductive energy harvesting device, an AC–AC frequency inverter, the transmitting and receiving coils, the rectifier systems connected in series, a wind turbine to drive the rotation of the receiving coils, etc. In particular, three receiving coils were designed for symmetrical disposition so that the angle between each pair of receiving coils was 120°. The design of the series rectifier circuit was explored to improve the input voltage level for charging the monitoring equipment more easily. The dynamic wireless power transfer system would bring about four energy-increased outputs with three symmetrical receiving coils when they were driven to rotate. The proposed scheme, born out of the existing methods of energy harvesting for monitoring equipment would provide stable and safe power at any time and it has been verified effectively by both simulation and experiment.

An opportunity wireless charging system for electric vehicles when they stop and wait at traffic lights is proposed in this paper. In order to solve the serious power fluctuation caused by random access loads, this study presents a power stabilization strategy based on counting the number of electric vehicles in a designated area, including counting method, power source voltage adjustment strategy and choice of counting points. Firstly, the circuit model of a wireless power system with multi-loads is built and the equation of each load is obtained. Secondly, after the counting method of electric vehicles is stated, the voltage adjustment strategy, based on the number of electric vehicles when the system is at a steady state, is set out. Then, the counting points are chosen according to power curves when the voltage adjustment strategy is adopted. Finally, an experimental prototype is implemented to verify the power stabilization strategy. The experimental results show that, with the application of this strategy, the charging power is stabilized with the fluctuation of no more than 5% when loads access randomly.

On-road charging systems for electric vehicles (EVs) have shown revolutionary potential in extending driving range and reducing battery capacities. The optimal equivalent load resistances to maximize receiving power of each EV according to different EV amounts are investigated. This paper introduces a typical on-road charging system with a single transmitting coil and multiple receiving coils. The equivalent circuit models according to different numbers of EVs are built. Power control strategies with regard to a varying number of EVs are then presented. Specifically, self-adaptive source voltage based on primary current detection is utilized to charge EVs, while the source can support enough EVs by providing the rated power. Otherwise, the source voltage is regulated to its maximum value and the charging energy of each EV is suggested to be controlled by adjusting the individual driving speed. A remarkable feature of the power control strategies is that the charging power for each EV is stable and can compensate for energy losses efficiently. As for urgent power demand from a particular EV with a low battery capacity, the adjustment of the corresponding load resistance is applied to alter the power distribution. The proposed technique has been verified in an experimental prototype.