A Wide Charging Range Wireless Power Transfer Control System With Harmonic Current to Estimate the Coupling Coefficient

In the wireless power transfer (WPT) control system, estimating the coupling coefficient ( k ) is an essential step to achieving optimal control over a wide charging range. The estimate required signal of the traditional WPT system is mainly the currentand voltage generated by fundamental. It requires many parameters and complex calculations to estimate k by analyzing these electrical signals, which makes the traditional method of estimating k difficult to achieve good robustness and application in practice. To reduce the process of estimation, a method of estimating k only by the harmonic current is proposed in this article. According to this method, a wide charging range WPT control system is designed. The main feature of the control system is that it is very easy to estimate k because the high frequency harmonic can simplify the circuit. By analyzing the system characteristics under different harmonic currents, the system can achieve optimal control over a wider charging range. In addition, a WPT system that meets the Qi standard is designed and tested. The experimental results show that the original 10 mm Qi standard charging distance can reach 20 mm.