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There are practical applications requiring the wireless power transfer (WPT) system to supply multiple output voltages to a variety of loads. In this paper, in order to achieve this goal, multiple double T resonant circuits are connected to the common port of the receiver side. Based on the modeling and analysis of the double T resonant circuit, it is found that the load-independent output and input zero phase angle (ZPA) can be derived. The proposed WPT system presents the following merits: 1) output voltages are load independent and can be controlled synchronously against the disturbance from input DC source and mutual coupling by using only one closed loop; 2) the output voltages can be adjusted individually to different levels by configuring circuit parameters; 3) only passive components are used to achieve multiple outputs. The power loss can be reduced due to the parasitic resistance of the passive component is very small and can be negligible; and 4) the reactive power losses are minimized due to the input ZPA of the system. An experimental prototype with two output channels is built, based on which the load independent and the controllable characteristics of the output voltages are verified. [ABSTRACT FROM AUTHOR]

Traditional wireless power transfer (WPT) systems usually adopt the single-phase-shift (SPS) control method to maintain a constant output current or a constant output voltage for various applications. However, the current-stress on one side is much higher than that of the other side especially under operating conditions with high voltage conversion ratio and light-load. This phenomenon actually can be proven by the established mathematical model of the current-stress of WPT systems using SPS control. This large current-stress will damage power devices and lower the efficiency of WPT systems. In addition, it will result in an increase of system total cost because of the need for the devices with the higher volt-ampere rating. A control strategy based on dual-phase-shift control is developed for WPT systems with an active rectifier to reduce the maximum value of current-stresses on both sides as well as to maintain a constant output voltage or current. Consequently, the system efficiency can be improved compared to traditional WPT systems with SPS control. A scaled-down experimental prototype is constructed to verify the effectiveness of the proposed WPT topology and the control method. Experimental results show that the proposed method can reduce the maximum current-stress significantly and improve the system efficiency compared to traditional WPT systems under SPS control. [ABSTRACT FROM AUTHOR]