Fast and Anti-starvation Charging Device Grouping for Magnetic Wireless Power Transfer

Magnetic resonant coupling (MRC) enabled wireless power transfer (WPT) can support charging multiple receiver (RX) devices simultaneously without the need for precise alignment. However, the charging performance of MRC-WPT systems is severely limited by impedance mismatching issues. RX grouping has been identified as an effective way to solve this problem, but has not been extensively researched. In this paper, we propose CharGroup, a fast and anti-starvation RX grouping mechanism that maximizes charging power in MRC-WPT systems. We first leverage the group-level impedance decomposability to obtain the equivalent impedance for all the RX groups rapidly by using a limited number of RX-independent measurements, and then filter them via impedance matching. Next, we use a two-level decomposition approach to capture detailed power distribution among RXs inside each group candidate. Finally, we perform time resource allocation among the candidates to ensure proportional fairness charging at the RX-level. We design and implement the CharGroup prototype, and conduct extensive experiments. The results validate the effectiveness of our scheme, i.e., CharGroup can achieve 462.67% and 21.06% average charging performance improvements over two state-of-the-art baselines, respectively, while guaranteeing RX-level proportional fairness.