Fast Maximum Efficiency Point Determination for Multiple Transmitters Wireless Power Transfer Systems With Unknown Receivers

Abstract

In wireless power transfer systems, particularly those with multiple transmitters (multi-Txs), transmission efficiency is a crucial performance metric for system evaluation. However, in practical operation, the receiver (Rx), especially its load resistance, can be uncertain due to the different charging status, which is not fully considered in conventional maximum efficiency point determination (MEPD) methods. In this article, a fast MEPD control method for multi-Txs WPT systems is proposed, which considers not only the coupling changing, but also the load variation. This control scheme is able to monitor both coupling changes and load variations by measuring the primary side current, enabling accurate determination of the maximum efficiency point. Furthermore, the dual-side communication and complicated calculation are not introduced in the proposed method, which largely improved the dynamic response. These enhancements are crucial for enhancing the user experience of wireless charging for portable electronic devices. By collecting primary current, both the mutual inductance ratio (MIR) and resistance ratio are derived. Then, by utilizing phase-shift control in primary inverters, the input voltage ratio is adjusted to be equal to the MIR, which satisfies the requirement of maximum efficiency point. The input voltage is finally determined by realizing constant output power. A practical system is built with two 100 × 100 mm transmitters (with 2 coils) and 200 × 100 mm (single coil) receiver. The results show that the MIR has the estimated relative error under 2%, and the resistance ratio under 7.5%. Meanwhile, the proposed scheme can maintain the system efficiency in varied coupling and load conditions, which is higher than 80.05%. The typical response time of the proposed MEPD is 12 ms. This article is accompanied by a video file demonstrating the proposed MEPD validation.