Noncoherent Power Combining for Free-Positioning Wireless Power Transfer in Large Area

In this article, we propose a new coil-energizing method for multitransmitter (Tx) wireless power transfer (WPT) systems that enable complete freedom of receiver (Rx) positioning in a large area. The principle is based on noncoherent power combining, where multiple Tx coils are supplied in a predefined pattern by mixing two slightly different frequencies and four different phase angles. The powers delivered from Tx coils at two frequencies are then combined incoherently at the Rx side, resulting in full positional and rotational freedom for the Rx charging. The power transfer blind spots in conventional WPT systems are completely eliminated with the proposed noncoherent power combining method due to its natural robustness against cancelations. The experimental setup shows constant dc–dc power transfer efficiency around 90% for arbitrary Rx movements without any further requirements on dynamic controls of Txs or Rxs other than the simplest activation/deactivation.