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.