Due to the electrical isolation nature of wireless power transfer (WPT) system, a method that can obtain the receiver side parameter only based on transmitter side information is desirable. However, typical estimation scheme assume that the coil inductance and compensation capacitance are constant, which will cause large estimation errors in high frequency system. Therefore, a multiple parameters estimation algorithm that can simultaneously identify load resistance, mutual inductance and receiver coil inductance is proposed in this paper, where only the input current and voltage are needed to be measured. Moreover, in order to cope with capacitor aging effect and manufacturing tolerance, compensation capacitance estimation algorithm is also presented. Mathematical model and algorithm procedure are depicted thoroughly and the gradient descent approach is adopted to obtain the optimal estimated parameter. The uniqueness of solution and the validity of this approach are strictly proved as well. Finally, a WPT experimental prototype with Class-D inverter is implemented and the experimental results are provided to verify the availability and accuracy of the proposed algorithm. INDEX TERMS Wireless power transfer, parameter estimation, gradient descent approach.

A foreign metal object will deteriorate the performance of wireless power transfer (WPT) systems and cause insecurity issues. Therefore, the influence principles and rules of foreign metal objects on soft-switching conditions of Class-E inverters and the performance of WPT systems are developed in this paper. The effects of different metal materials on coil parameters at different frequencies and positions are analyzed first, then the effects of foreign metal objects on soft-switching conditions of Class-E inverters and the power transfer capability of WPT systems are investigated. Principle analyses and simulation results demonstrate that there are significantly different effects on the soft-switching conditions and power transfer when a foreign metal object is placed near the transmitter coil or the receiver coil. In addition, the monotonicity of the variation in power transfer also depends on the position of the foreign metal object. Finally, a WPT experimental prototype with a Class-E inverter is implemented to verify the influence principles and rules of foreign metal objects. The experimental results are highly consistent with the principle analyses and simulation results.

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