Multistate Voltage Balancing of UAV’s Cell String: A Reconfigurable WPT-Based Multiport Hybrid Charging Approach

Wireless power transfer (WPT)-based voltage equalizers (VEs) are desired for flexible and secure balanced charging of unmanned aerial vehicles (UAVs). However, the existing WPT-based VEs fail to balance the cells once the onboard receiver (Rx) is away from the transmitter (Tx), and the efficiency and capacity are limited. This article proposes a reconfigurable WPT-based multiport hybrid charging approach to achieve UAV’s cell string balancing under multiple states. By converging one Tx port, one Rx bidirectional port, and two voltage-balance (Vx) driving ports, the approach enables the source-to-cell (STC) and pack-to-cell (PTC) charging/balancing, which achieves cell balancing during charging, discharging, and standing conditions. Circuit analyses of the corresponding topology validate its operating principles and basic performance. Efficiency and capacity in the STC balance mode are improved with the combined Rx and Vx output ports. The cell’s voltage equivalation can still be realized without Tx in the PTC balance mode. Asymmetric Tx and Rx coils and orthogonal Vx coils integrated into Rx are designed with specific coupling or decoupling as the multiport WPT coupler to enable the charging and balancing with a robust misalignment tolerance. An experimental prototype for eight cells is established, and the test results demonstrate the effectiveness of this scheme.