Fault Detection of Coil Misalignment in Multi-Receiver Wireless Power Transfer Systems With the Estimated Mutual Inductance

In a multi-receiver wireless power transfer (WPT) system, mutual inductance is a key determinant of electrical performance. In small mobile-device applications, receivers (RXs) can be placed or moved arbitrarily on a single transmitter (TX) pad, making coil misalignment unavoidable; therefore, reliable fault detection is essential for stable operation. This study proposes a two-stage approach to estimate the full set of mutual inductances. In Stage 1, each receiver is sequentially activated with a fixed pulse width modulation duty cycle to estimate the TX–RX mutual inductanceMTiand equivalent load resistanceReq,i. In Stage 2, receiver pairs are activated under the same condition to estimate the RX–RX mutual inductanceMik. Then, misalignment faults can be detected by comparing the estimated mutual inductance values with predefined thresholds. A three-receiver prototype (10 mm airgap) validates accurate mutual inductance estimation and reliable fault detection.